UTAS build thread [Archive]

Claude Rouelle

03-18-2014, 06:03 AM

One comment and one question

A chassis is just a big bracket that is supposed to
a) respect the rules especially safety
b) sustain the forces coming from the tires
c) hold all the elements such as engine, diff... and driver
d) with best possible ergonomy
e) with the best compromise between weight, minimized compliance and manufacturing cost

So the comment is that it is difficult to evaluate your chassis on these pictures without
1. Seeing all the suspension pickup points
2. Seeing the engine, diff, master cylinder, pedal box, seat belt, steering column, steering rack, radiator, wings (if you have) maybe even bodywork parts attachment, etc mounting points
3. Having an idea of the targeted weight and torsional stiffness (at least by calculation)
4. Knowing your targeted wheelbase, tracks, weight, engine choice and aero configuration
5. Knowing your tire choice (at least sizes)

I would prefer to see a design (elaborate CAD or simply a good complete sketch). Can you do that? (I hope you have not started to manufacture your car without having finished most of your car design; that is the trap in which 90 % of the students fall)

The questions (which I remember my mechanical engineering / design teacher asked me many years ago);
1. In your opinion what is the weakest point in the chassis? (I can already see a few even without the suspension and other elements pick up points)
2. If you have decided not to improve this weak point (points), what is the compromise that you have made to accept such a weak point?

I wish more students would post such pictures and drawings and ask for observations. It is courageous and helpful for the whole community.

These are my first observations. I am sure other experienced person (I am mainly thinking of Pat Clarke and Geoff Person aka Big Bird and Tobias but also several good alumni) would come with many other valuable comments.

Jonny Rochester

03-18-2014, 06:51 AM

Thankyou Claude,
I joined the team as a student, after some other final year students had already done a chassis design (they imagining side engine). Initially I had to go along with them until I had done my own research. After visiting FSAE-A and spending the summer TIG welding this chassis for them, I have guided the team to a rear engine traditional FSAE setup. With the chassis in place, we have spent some time sitting in it, getting familiar with all the components. Design work continues in Inventor, but I like to play with the real thing. Now after measuring some stuff and looking at it, I have led the team to change the chassis design. A few weeks ago the CAD was looking like this:
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/CADchassis.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/CADchassis.jpg.html)

The front of the chassis will be changed to comfortably fit the 350x350 template in the leg area, with a steering rack on the floor, and the pedals on a sliding false floor. The first design was not designed around many components...

The side intrusion section may get some extra bracing, thinking of torsional stiffness. But how stiff is stiff enough? The students here like the idea of FEA, I'm a bit old school myself.

The engine is a single 450cc, from a BMW G450X dirtbike. Has this engine been used in FSAE before?

Tyres will be 20" x 7"? - 13" Hoosier. Wishbones and pushrods, FSAE by the numbers as far as possible.

Pat Clarke

03-18-2014, 07:13 AM

Johnny,

Further to what Claude says, I have two comments.
A very common error is to build the chassis first and later adapt it to fit steering, suspension, powerplant etc. This 'adaptation' always adds complexity and weight and usually reduces stiffness and access. The chassis is a bracket to hold everything together and actually should come later in the Design process.

Secondly, and potentially more serious.

It appears your roll hoop has a welded joint at the top of the chassis (It might be an optical illusion). The rules require the hoop to be bent from a single tube, going from the bottom of the chassis at one side and across to the other. If your hoop is welded on top of the chassis, it will not pass tech inspection and will not be allowed to compete. :-(

Where will you put the steering rack? remember, your chassis must pass the 'template' tests.

Regards

Pat

Jonny Rochester

03-18-2014, 07:37 AM

The error of building the chassis was beyond my control, as I tried to say. But also, it's not such a bad thing. Consider that most teams build a mockup out of wood or PVC tubes. It only takes a bit more to build the real thing. All the better for practice welding. A grinder can cut that thing in half very very quickly. Not too hard to change... And we build workshop skills in metalwork, not woodwork!

Another idea: Only since we built this chassis, we had a physical object that people could visualize or identify. I believe it helped assemble the team, having that physical thing. In a new workshop, you know it takes about 2 weeks just working out where the light switches are and where the tools are kept. For myself and the students (most are not tradesman) it's good to just start making something, anything.

The main roll hoop is 1 piece.

Steering rack is top secret.

Pat Clarke

03-18-2014, 08:02 AM

That is good news. I had visions of you having to throw it away and start again.

Sorry I missed your earlier comment that the rack will be on the floor =]

Pat

Jonny Rochester

03-18-2014, 07:46 PM

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/054.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/054.jpg.html)
I cut up all the wishbones from our 2002 car. We will use the same again, different dimentions. I am recycling some spherical bearings and tubes. They are 3/4" 4130 lower tubes, 1/2" 4130 upper tubes. Lower bearings are 7/16" Aurora, all 3 joints. Uppers are 5/16" bearings, all 3 joints. Bearings are held in a bucket with circlip. I have got the workshop to make new buckets on the CNC, but I will recycle some tubes with bearings still in them if I can.

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/057.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/057.jpg.html)
I did a test weld on new CNC buckets to check the bearing clearance after welding. It will be a small clearance fit with bearing retainer and circlip.

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/035.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/035.jpg.html)
I attached the front upper clevis to our new frame, saved from the old car.

Claude Rouelle

03-18-2014, 09:39 PM

John,

- Again it would be nice if you can post several drawings of the whole car with steering rack, steering column, engine mounting points and engine components (inlet manifold, exhaust), differential and its attachments points on the chassis, fuel tank, seat belt anchorage points, suspension and damper brackets, etc....

- 7/16 and 5/16 joints ...Oh my God... Are you building a truck? Is your car going to be 500 kg? How did you come to this rod end or spherical joint size choice?

- Not sure In understand the tube between the chassis and the suspension bracket

- Do you machine the hole for the spherical ball joint before or after the welding of your wishbone? Do you use one shoulder and one circlip or 2 circlips to hold the spherical ball joint in its housing?

- Where in your opinion is the weakest point in your chassis? In other words in normal racing conditions and /or in case of crash / impact where would the chassis bend or twist or break? What would be the conditions in which these damage would occur? How did you come to these conclusions?

Jay Lawrence

03-18-2014, 10:16 PM

Jonny,

Just a couple of comments:
-The front roll hoop looks pretty tall, not sure if that will make bodywork a pain/unattractive
-Not sure what you (?) are sitting on in the first picture but you might have trouble with helmet clearance
-Why did you build the lower chassis section as a ladder?
-As far as I am aware, no-one has used the G450 engine. I've read they are built by Kymco in Taiwan and have regular rebuild intervals (correct me if I'm wrong)
-Do you have experience tuning a 450 single? Many teams have struggled to get theirs working/starting reliably (although the dry sump and factory fuel injection will probably make things easier...)

I definitely agree that it can be a massive leap forward to just build SOMETHING and go from there. Certainly a good way to get morale up and get people involved. Claude, I would argue that to a certain extent it's not a bad idea for a first year team to 'build first and design later'. If nothing else it stops people from getting trapped in the 'optimisation' loop during the design phase, and gains a very valuable practical insight.

Pat Clarke

03-18-2014, 10:37 PM

A few more comments Johnny.
The inner location of your front wishbones will significantly compromise your suspension geometry. Have you designed your suspension (Uprights etc) yet)
Mounting the clevises to the sheet metal extensions will materially affect the installed stiffness of the chassis.
The bend in the upper cockpit rail will murder the beam stiffness (already marginal) of the chassis.
Why was it necessary to add the additional bay to the rear of the chassis (first to second picture)?

To address some earlier points.
I agree the dashboard bulkhead is probably too high.
We have seen the BMW engine used in Germany.
Ultimate chassis torsional stiffness may not be as important as some might believe. 1000ft/lbs per degree might be a figure to aim for.

Pat

Jonny Rochester

03-19-2014, 05:53 AM

Claude,
-I can't show you the whole car as it is in secret development (code for not yet designed). Major parts are designed by some 4th year students as their honours project. And in Australia those reports are not submitted till about October/November? However we are planing to have the car running by June/July.

-7/16" and 5/16" spherical bearings are chosen for a very good reason, it's what the old car had. :o
But I have found drawings of a Formula Ford that generally uses the same bearings, but they use reducers to accept a smaller bolt. eg: 7/16" sphericals with reducers and a 5/16" bolt. And on other places 5/16" bearings with reducers and 1/4" bolts. With the celvis bolted to the chassis using a mixture of M8 and M6 bolts. I'm talking about Swift Cooper SC95 chassis. I'm drawing some influence from well designed Formula cars rather than student designed.

-The bucket for the bearing will be machined first. It will be setup for welding, it will be quickly TIG welded by an expert student (myself). Remove scale and the bearing should go in perfect. (See test sample above). We use a shoulder and 1 circlip.

- as for weakest point in chassis... It may not matter, because if we build to min amount of metal as per the rules, that may be strong enough regardless of poor triangulation. Did you ever see a legal FSAE car that could not compete due to chassis flex through the middle?

Jonny Rochester

03-19-2014, 05:57 AM

Jay: - The front hoop (dashboard) only looks tall on our welded chassis, because it is too narrow, and because the front bulkhead is probably too low. Looking at the CAD picture, that is changed. The ladder chassis was designed in 2011-2013 by former 4th year students.

-The BMW motor was chosen for a very good reason. It was given to us.

Jonny Rochester

03-19-2014, 06:23 AM

Pat: The uprights are being designed in an engineering design class, however they are only designing the materials, weight, stiffness and a few clearance issues. I have designed the geometry of the uprights myself (after some group meetings using a white board and a few scribbled diagrams on an envelope). So the geometry of the uprights is fixed, and known, (and constrained a little as we are using the old cars wheel bearings and axles etc.).

-I can't agree with you about stiffness of our suspension bracket. It is only tack welded for now, but it will probably get changed. Very similar design, but may use welded in studs rather than welded captive nuts. With captive nuts we may have to drill and wire the bolts. With studs we can just use nylocks.

-The extra chassis bay at the back is for orange jacking bar, and rear trailing wishbone mounts.

BeunMan

03-19-2014, 08:27 AM

...

-7/16" and 5/16" spherical bearings are chosen for a very good reason, it's what the old car had. :o
...

We sarcastically have a tile hanging above the maintenance bay which says "Because they did it like this last year..." (in Dutch "Omdat het vorig jaar ook zo was..."). Try telling that to the judges.

On your note to the Formula Ford: Those cars are over 400Kg dry and have a lot higher loads to process. You can get your car up to that weight but then you break the tilt table (as happened at FSUK once).

Claude Rouelle

03-19-2014, 11:53 AM

Jay

" I would argue that to a certain extent it's not a bad idea for a first year team to 'build first and design later"

I totally, totally disagree with you. That is the worse habit to acquire for news designers/manufacturers. It is bad project management to start building car without ALL the components being part of the design.

I see every year too many FSAE/FScars where it was clear that the students started to build their car without thinking about where to put the muffler, the ARBs, the steering rack, the radiator(s), what the shape of the fuel tank will be and where the seat or the seats belts will be attached. The car ended up being a mess, look bad, weight more, often loses structural integrity or do not pass tech because for example "we had to cut that tube to install this part'

It ends up costing more time and more money, it creates frustration and tensions in the team. It shows the inability of the team members to use their imagination of a complete product and to control their emotions by rushing to a "touchable" but unfinished concept.

Mistakes are often caused by making a decision without sufficient information or evidence. Starting to build a car without accumulating enough evidence of where each car components is situated is a big mistake.

Claude Rouelle

03-19-2014, 02:28 PM

Jonny,

BunMan is right on when he writes "Those cars are over 400 Kg dry and have a lot higher loads to process"... while you car should be in the 200 kg (monocymonder) 230 kg (4 cylinders) maximum driver and fuel included.

For the same lateral, longitudinal, vertical accelerations with less mass you will have less forces and so for a given stiffness target less material will be needed so less weight and so on..... To push the reasoning at the extreme....how big would your chassis torsional stiffness need to be if your mass was 0 Kg?

The lighter the car is the lighter it can be.

Claude Rouelle

03-19-2014, 02:43 PM

Jonny,

"- as for weakest point in chassis... It may not matter, because if we build to min amount of metal as per the rules, that may be strong enough regardless of poor triangulation"

Ok let's say you are right... if your goal is "just to compete" but that is not in the spirit of FSAE/ FS competitions which are engineering exercises. What about performance? What about response? What about driver ability to feel and control the car which has a chewing gum (and probably a huge hysteresis) between the front and the rear wheels?

*****

"The bucket for the bearing will be machined first. It will be setup for welding, it will be quickly TIG welded by an expert student (myself). Remove scale and the bearing should go in perfect. (See test sample above)."

Wrong. The hole for the bearing will be deformed in the welding process. You might still be able to press the bearing in the hole but you will have huge friction which are detrimental to handling and driver feedback. Make a small hole for your jig. then weld, then re-machine with the eaxt tolerances.

*****
"We use a shoulder and 1 circlip" So if the shoulder is that important to avoid the bearing to be dislodged from its housing, your left front top wishbone cannot be used on the right front, correct? So more spare parts, correct? Up to you if you want to work had or work smart.... Have a look in catalogue and see how much axial force a circlip can sustain; no need for a shoulder.

jose_90

03-19-2014, 06:47 PM

BunMan is right on when he writes "Those cars are over 400 Kg dry and have a lot higher loads to process"... while you car should be in the 200 kg (monocymonder) 230 kg (4 cylinders) maximum driver and fuel included.

230 kg including the driver? That would mean for a 70 kg driver, 160 kg?

Jonny Rochester

03-19-2014, 08:21 PM

All the small details, the nuts and bolts of the wishbones, I have my head around that. You missed the bit when I said I had already done a test weld, pic included? We have the capability to machine stuff if needed. But workshop time is valuable. And a shoulder is better than a circlip. And buying 1 circlip is better than buying 2. And machining 1 groove for a circlip is better than machining 2.

But some things are more important than others. To me, it is about getting a drive-able car, and that is linked to cost. It's not about the cost report, it's about real money to buy real things. Using a few 7/16" spherical bearings is not going to blow the car from 200kg to 500kg. Instead it is going to build in reliability, and save real money. The tilt jig is capable of 2000kg. All the rod ends and bearings will be from our 2001 car. The students are dumbfounded that these Aurora bearings measure funny and are not metric, as we havn't been taught inches yet in our degree.:eek:

Claude, I was going to say you are wrong about many assumptions you have about our team, and that you are even wrong about the competition. But I was the one that lay the bait. You took it, hook line and sinker.

But I will say this. You can not give me an example of a team that designed a whole car from scratch in CAD, then just built it with minimal changes. If you do try and give me an example, it will just say that that team had the previous years car to work from, which effectively was the "try it and see" proto-type.

Also, if this is just an engineering competition, then the students should not have to build anything (unless they themselves are qualified tradespeople). If this is just an engineering competition, then the students should not have to drive the car, because then it would be motorsport (which it is).

Jonny Rochester

03-19-2014, 08:58 PM

But we have spent a lot of money on this:
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/1977015_264470440393882_1100783394_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/1977015_264470440393882_1100783394_n.jpg.html)

It's not my project so I can't speak about this. But it will be data acquisition of chassis stress/movement/stiffness, as well as logging suspension movement. The focus will be on chassis, not suspension.

03-19-2014, 08:58 PM

Jonny,

First the good news.

I agree with Jay that your approach of "build first..." is good for an inexperienced team like yours. As noted, getting the other students motivated by having something real to sit in can be a huge factor in improving your end-of-year results. The fact that you are also ready to modify whatever you have built, based on what you have learnt from the last build (eg. not enough foot/elbow/engine room, or whatever...) is also good.

The truth is (IMO :)), MS tubing is dirt cheap, and the build time doesn't cost much either (especially while you are enjoying it), so you will be learning far more by following your approach than by sitting in front of some myopic CAD box. In fact, I reckon the only advantage of spending a year looking through the keyhole of a typical CAD system, is that it better prepares you for a future career as a gynaecologist!
~~~o0o~~~

Now the bad news.

The pictures of your first frame are down there with the worst FSAE spaceframes I have ever seen (well, not including the Indian efforts :)). But your CAD image is EVEN WORSE!

SIMPLIFICATE! Add fewer tubes. Add fewer nodes. Add fewer bends... The tubes that are mandated in the Rules are almost all you need. You are using an engine at the lighter, lower power, end of the spectrum (= the best end, IMO), and hopefully also 10" wheels (?), so you DO NOT NEED the Sydney Harbour Bridge to hold it all together.

Your current frames (built and CAD) have very little torsional stiffness. I know this just by looking at them. :) Please measure the Nm/deg of your built frame. It only takes about an hour of simple testing to get an answer within 10% (ie. 90+% accurate, which is much better than most team's (non-) number!).

Randomly adding more diagonals won't improve things. A sheet steel floor might help a little, and you need a floor anyway (spot weld in 0.6 - 1.0 mm galvanised sheet). Perhaps increase the diameter of the main longitudinal tubes (top and bottom SIS) to, say, 30-40 mm. Keep them same wall thickness, but make them straighter (just slight outward bow, front to rear).
~~~o0o~~~

Finally, Curtin U came second at FSAE-Oz 2013 with a car that weighed 260-280 kg (with NO driver or fuel!). I believe their overall approach was similar to yours of build->test->improve... (Though much different overall philosophy of four+wings.) So don't worry about your rod-ends being TOO big (maybe a few hundred grams extra, all up?).

Oh, and if you manage to build->test->improve a car that can actually drive 30 kms, at an average speed of ~50 kph, then you will beat half the other teams at Oz-2014. Many of the teams below you will have followed Claude's advice.

Z

Jay Lawrence

03-19-2014, 10:39 PM

Claude,

I was pretty sure you would disagree with the 'build first, design later' approach. I understand that and I fully understand that in the professional world of racing (or even more so, consumer cars) there is too much money flying around for this to work (you can't keep going back to expensive suppliers with slightly tweaked designs and expect fast delivery, for example), but in this category I think it can work. In fact I believe the first Wollongong car was built that way (including some Formula Ford bits as per Jonny's car), and it was lauded as the best first year car ever. Anecdotal I know, and there are plenty of rubbish first year cars, but it can work.

I do agree about the spherical/welding issue though. For a while we ran a spherical cup with a circlip on one side, but then moved to staked Aurora bearings, which is neater and eliminates the circlip. Either way I don't think they should be machined to size then welded, regardless of how good you are at welding. Compliance is a killer and having a misshaped bearing housing doesn't help. But hey if it works it works

Claude Rouelle

03-19-2014, 10:47 PM

Jonny,

You should not spend money on data acquisition, especially with National Instrument who love collaboration with universities. If you know how to sell your dream these things should be free of charge for a FSAE / FS team.

Claude Rouelle

03-19-2014, 10:56 PM

Jonny, Jay.

University of Bologna went to FS Spain in 2011 (I was the chief design judge) where there was only about 20 cars but they won the design competition and finished second overall. It was their very first competition. Their faculty adviser did not allow them to access any machining and the workshop until the COMPLETE design was finished. The whole car, jig included, was built in 7 weeks. There was no surprise, no missing parts, no unnecessary over time or over budget. Pretty good example of thinking before building.

Jonny Rochester

03-20-2014, 01:09 AM

Claude,
I just googled Bologna, and it seams you missed somethings in translation. They had comprehensive designs in 2008, a complete car in 2009, and competed at both Italy and Spain in 2010. And since this they compete at 3 FS events per year, 2011 included, as they are in Europe and can travel. And they have 60 people. So you got that wrong.

But lets just imagine Spain 2011 was their first event, and they did ALL design work first (without having knowledge of any physical fsae car). This means that when the chassis was welded by a student, that was the first time that student had done any welding. When the axle was machined, that is the first time the student had ever used a lathe etc. And nothing went wrong...

Jonny Rochester

03-20-2014, 01:24 AM

I agree that it is good to aim for a complete CAD assembly before building. Not always possible.

The bearings will not have to be pressed in, it is a slight clearance fit. Loctite bearing retainer will be used as previously mentioned. Going to staked Aurora bearings would be nice, but that would require buying new bearings with the G groove. Unnecessary cost.

Jonny Rochester

03-20-2014, 05:33 AM

I am having trouble finalizing the seating position and knowing where the pedals should go. There are so many variables, it's hard to know what to anchor. It's hard to sit inside a CAD model. How do we do it?

(Never mind the torsional stiffness issue, chassis not finalized, it's just a bracket!)
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/1797964_10152104469154667_1372863288_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/1797964_10152104469154667_1372863288_n.jpg.html)
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/1458427_10152104469149667_402231687_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/1458427_10152104469149667_402231687_n.jpg.html)
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/1966895_10152104469119667_1939745402_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/1966895_10152104469119667_1939745402_n.jpg.html)

03-20-2014, 09:32 PM

I am having trouble finalizing the seating position ...
It's hard to sit inside a CAD model. How do we do it?

Jonny,

I'm pretty sure you know how... ;)

More to the point, I reckon your chassis could be about half a metre shorter. This would give it lower mass, more stiffness, lower Yaw inertia (probably the most important one here), so better all up.

To do this, push the engine further back, so shortest chain run that works, and diff possibly behind axle line a bit (10 cm is OK). Then push the driver further back too, so the seat-back is as close as feasible to the cylinder head and exhaust (couple of cms is OK). Then think about a neat and tidy foot/pedal-box area, with no unnecessary forward overhang.

Then, get rid of about half the tubes in the above images!

Nevertheless, congratulations on progress for Oz-2014 so far, and for posting all your work here.

Z

(Edit: PS. Your 4 x main longitudinal tubes (top and bottom SIS) each have two bends in them, at the FRH and MRH. I suggest they only have a slight bend at the MRH, then straight-line to the Front-Bulkhead. Straight lines are always easier...)

nowhere fast

03-21-2014, 12:06 AM

It's hard to sit inside a CAD model. How do we do it?

Jonny,

I’m not sure if your last post was tongue in cheek, but my team would mock up the driver position in two stages.

First we would put drivers on a mock up seat back made from wood that we could adjust the seat back angle on, and then measure where their feet and hands needed to be.

Once we had a rough chassis design (developed on a whiteboard and in CAD) we would make a physical mock up from wood or cardboard (our chassis’ were made from folded aluminium panels) to check ergonomics, visibility, packaging, etc.

I agree with Z about moving the engine and driver further back and as close together as possible; but will add that another advantage is increased rear weight %.

Finally; it’s good to see UTAS returning to FSAE, and it’s interesting to see your progress in this thread.

Thijs

03-21-2014, 06:08 PM

For what it's worth, I'm pretty sure Claude meant FS Spain 2010, where Bologna won design and endurance. It was actually their second event, but still their first car.
They finished 16th out of 40 overall in Italy a month or so earlier, 19th in design, 19th in endurance in a much more competitive field.
A fine performance for a new team, and perhaps more indicative of how good the car was, because honestly, FS Spain was very uncompetitive that year. There were 11 teams there, the overall winner was 333rd on the WRL.

A team that really impressed me was Vienna in 2008. They finished overall 4th out of 77 teams at FSG that year with 839 points. That was their first car.
Unfortunately I never got to talk to those guys, but I've never seen such build quality on a first year car.
Purely judging from that I'd say they must have had their design in order by the time they started building.

Thijs

Jonny Rochester

03-24-2014, 07:30 AM

Yes, half my comments are tongue in check. But genuine questions about other things. We have done the thing where you sit in it, whiteboard behind, grid drawn on whiteboard, take a photo etc...

Fast tracking to some other issues. This is a current suspension design some boys are working on today:
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/1979713_10152112680019667_1108544912_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/1979713_10152112680019667_1108544912_n.jpg.html)

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/971554_10152112679874667_119035872_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/971554_10152112679874667_119035872_n.jpg.html)

I myself prefer inboard Formula Ford style. What do you think?

BeunMan

03-24-2014, 07:41 AM

Quick look: Rodends in bending?

See: http://www.formulastudent.de/academy/pats-corner/advice-details/article/pats-column-rod-ends-in-bending/

Jonny Rochester

03-24-2014, 07:55 AM

This is for front suspension if not clear. (Rack not pictured yet).

Please delete your rod ends link, as that is no what is depicted here.

Pat Clarke

03-24-2014, 08:23 AM

Johnny, have a look at the forces on that rocker pivot bracket and the shock mount bracket. Where do the forces go?

Pat

Jonny Rochester

03-24-2014, 08:50 AM

Pat,
Unhelpfull (Answering a question with a question)

Pat Clarke

03-24-2014, 08:59 AM

Johnny,
It is not for me to design your frame.
FSAE is an engineering design competition (despite your stupid statement to Claude!).
You are the competitor, supposedly the designer.
I have pointed you to a serious design error.
That should be help enough.
But obviously you don't need it, so that's the last from me.

Pat Clarke

Auerbach

03-24-2014, 10:51 AM

I am thoroughly enjoying this thread. I haven't visited this forum in many years but I needed some information for an FSAE rebuild.
I have no dog in this fight so take this with a grain of salt, but I'm loving the slight undertones of tension between the posters. I can appreciate Johnny's courage in posting such detail and having decent answers for the questions, even if they aren't based on supreme engineering optimization. I think the likes of Pat and Claude, who deserve great respect for who they are and what they have contributed to FSAE, sometimes suffer memory loss on how some novice teams operate. Previously I mentored a team of rookies and I can attest that none of them would know if a chassis was made of chewing gum just by driving it. When I joined FSAE at UT Austin, I'd never driven anything that didn't have 4wd and a bed. Johnny's team might only be 5 guys with 0 faculty support or leadership and he seems to be consciously selecting the best path for they're situation, all the while using this forum to determine what can be improved without asking for handouts.

To me, FSAE is about learning. That level of learning is highly dependent on the program at each university and the nature of FSAE leads to a large variety of programs.
Some students learn how to just "build a car", soaking up as much knowledge from what is a TIG welder to what is inelastic weight transfer.
Some students get into the fine art of shock tuning, roll moment distribution, understeer gradients, etc
Some students hone their CNC machining skills, pun intended.
Some master precision trail braking and apex clipping.
Some eat gas station burritos, drink red bull and make beautiful CAD assemblies.
I could go on and on, but none of this occurs without the ultimate goal of building a running car and competing with it.

That being said, Johnny, your frame is poorly optimized, your bellcrank mount is piss poor, you should do more in CAD, and your sphericals are too large, but I like your first post and the look on the driver's face so you're a winner in my book. Keep up the good fight.

Auerbach

03-24-2014, 10:52 AM

Canuck Racing

03-24-2014, 11:39 AM

Johnny,

I second everything that Auerbach and a few others have said. Keep up the good work. As long as you can come up with a car that can reliably move under it's own power and keep 4 wheels on the ground (well - maybe an occasional 3 is acceptable) you'll do far better than most teams. Not just first year teams. All teams. No matter what competition you enter, finishing endurance and making an attempt at all events will probably put you in the top 1/3 of competitors, and the only way you can expect to get there is with a well built (not necessarily well designed) and tested car. The most beautiful and complete CAD model and design report won't mean a thing when the green flag drops.

Jonny Rochester

03-24-2014, 02:01 PM

Auerbach and Canuck,

Thankyou for your observations. You are probably correct in those ideas. Counting active members that design and make stuff, we are a small team. Most of the designs here are not my own, but I have led them away from worse (side engine with 2 chains etc). I have my own ideas, I can see the obvious. I need to get better at Inventor, the CAD here is not my own. I personally am not a final year student in charge of design. But anyway...

Pat,

I just don't like getting a question in response to a question. Don't take it too hard.

Rex

03-24-2014, 02:15 PM

I think the likes of Pat and Claude, who deserve great respect for who they are and what they have contributed to FSAE, sometimes suffer memory loss on how some novice teams operate.
Agreed. I think part of this tension is the ever-widening disparity in FSAE of the haves and have-nots. So many teams are so good these days that the new/small teams can't possibly be taken seriously in comparison. And that's no fault of anyone involved, it just is what it is. But if you've got 3 guys in a shed with a welder (which feels like a common post genre lately), there's a lot of advice floating around on this forum that I would actually classify as "bad" advice. Bad in the sense that it won't result in those teams having any chance of finishing a car, or at least questionable in that it would be unnecessarily burdensome and a waste-of-time to a team that's still trying to understand the most basic of things about vehicles and engines. REIB is one of these items for me, but that's a different fight for a different day I suppose. :)

I also think it's really interesting to see Pat and Claude's overall input on this forum and how widely it varies. Sometimes it's super helpful, sometimes medium helpful, and sometimes reverts to telling people what the self-proclaimed rules of the forum are. I think part of the underlying tension in this thread is due to this ever-changing dynamic between organizers/judges and students - as judges become more accessible their value-add to the FSAE community certainly goes up overall, but tensions also develop based on how that help is delivered at various times. It's like moving in to live with your significant other...all of a sudden a small inconsiderate turn-of-phrase results in hurt and resentment, primarily because of the more constant interaction. Same story here I think. Except that the difference here is that most snarky judge comments are met with responses like "sorry sir" because of the position-of-authority issue, which seems a bit of a shame to me because snarky is snarky no matter who you are.

That being said, Johnny, your frame is poorly optimized, your bellcrank mount is piss poor, you should do more in CAD, and your sphericals are too large, but I like your first post and the look on the driver's face so you're a winner in my book. Keep up the good fight.
All true! But I bet if he built it and drove the hell out of it, most or all of these things would be OK from a "will this thing function" standpoint. Like Canuck said, a running car is already above average in terms of collecting points. If a new underfunded and under-manned team's goal was to finish top 50%, I suspect a 24/7 testing venue (and a small budget for gas/tires) would be their most valuable asset, with a decent MIG welder a distant second, and a machine shop possibly not even on the list. With that said, I absolutely agree that a day or two of CAD optimization in this particular instance would go a LONG way...then build it, drive the hell out of it, and finish in the top 50% at competition. In any case, keep up the good work Johnny & co.

Jonny Rochester

03-24-2014, 02:45 PM

Our suspension in general: We want about 2-1/4" wheel travel up and down. Our Fox DHS RC shocks have about 2-1/4" travel from free length to compressed. The pushrod is at about 45deg which means it travels about 0.707" when the wheel moves up 1". So we want a rocker ratio of 1:0.707 or 1:1.4. At normal ride height (chassis 45mm off the ground) the shock should be about 30% compressed and the angles in the rocker should be perpendicular to the pushrod and shock. To finalise the design, we should make sure the shock pictured in CAD is ~30% compressed, and the pushrod to rocker angles are OK. At ride height, the pushrod, rocker, and shock should all be in the same plane. If the pushrod moves out of plane with the rocker with suspension travel, that is probably OK. Have we got that part right?

For the shock position above, it could be made to work. The lower mounting bar does not need to be there. The rocker bracket looks awkward but necessary. Anti-roll bar is not yet designed.

But this is what I'm pushing for:
http://www.ellerymotorsport.com/images/restos/7-large.JPG

I want the shocks up the top like this. Team members are worried the pushrod will be too long, the pushrod will go out of plane with the rocker. And the biggest hurdle, it's difficult to draw those angles in CAD and design our chassis around it.

Claude Rouelle

03-24-2014, 05:03 PM

Johnny,

No need to be rude. People, are trying to help here. A snap "unhelpful' does not make anybody a winner here.

Claude

Claude Rouelle

03-24-2014, 05:20 PM

Jonny,

1. If you want to use inboard damper why do you put them nearly vertical? Why don't you put your dampers horizontal (or nearly horizontal) and lower. (that means pushrod with I reckon a bit of accessibility issues); lower CG, better centered mass, better aero and less disturbances of the wings, radiator flow etc...,

2. You should try to have the axis of your pushrod going through the lower outboard wishbone ball joint to reduce compliance

3. Whether you like it or not Pat is right: your rocker axis is in a middle of a tube and so is the lower damping mount. Pat is an international design judge; you are lucky there no point in the design competition for student attitude. Well....maybe..... if the only way you can defend your engineering choices is by using harsh words.....

I command your desire to learn and doing so by exposing your design to criticisms and from there exposing your lack of knowledge. Bravo! But there is no need to be that rude.

If you answer your girlfriend with the same style, and if she is smart, I bet what you will get back is what you will deserve: a slap on your face. Have fun!

Edward M. Kasprzak

03-24-2014, 06:41 PM

Sometimes I think Pat is too blunt. Pat probably thinks that I'm not harsh enough sometimes. I could make a similar comparison with Claude and vice versa. The fact is that everyone doesn't speak in the way you need to hear something, and everyone is doing their best to educate today's university students. Pat's approach reaches students I don't as easily, and vice versa. In my role as a classroom teacher I learned long ago that some students respond well when you pull them aside quietly and have a heart-to-heart talk about whatever the issue is. Others respond best when you call them out in front of the whole class. Get the wrong approach with the wrong student and the desired response will not follow.

Of course, an inherent respect for fellow students and DJs is absolutely essential. The only time I am truly upset is when someone crosses this line. One can be harsh but not disrespectful.

On this forum we DJs don't have much to go on when we meet students. You get the response style that you get depending on who answers. Maybe the style works for you, maybe it doesn't. Don't lose the underlying message. It's very sad when students don't want to listen. In another thread I answered someone's question with a question and it has led to a pretty nice discussion. In this thread the response was effectively "my ears are plugged and I'm not listening." Now it's "the DJs are out of touch". Sigh.

By the way, three guys with a welder can still exercise good engineering fundamentals. In fact, the project may be easier because the management issues with one-, two- or n-dozen people won't exist.

I review every design report in the North American competitions every year. Pat and Claude can speak to worldwide trends. Don't kid yourself about the quality of the field. Most schools do not simply draw and weld a car together. Sure, every team (EVERY team) has shortcomings, but there's a lot of good engineering going on. As an engineering competition I find this to be very satisfying. Don't rationalize your way out of engineering your car, and don't overlook the fundamentals in favor of detail design.

Of course, this is the one major problem with Formula SAE/Student: automobiles are just so darn robust. You can build the worst possible car and it will still function at some level. It may not be fast or run long before breaking, but it will go. And tinkering can get you decent results. A significant portion of the competition is performance-based. Yes, you can tinker your way to good scores in the dynamic events, especially since you don't need to design/build your tires or engine! But not every field is as robust as the automobile. The engineering processes and responsibility for fundamental knowledge stressed by the DJs will serve you well in your future careers.

Not convinced? Consider this: My area of vehicle dynamics did not really get going until the late 1920s or early 1930s. That's DECADES after the car was first developed. Meanwhile the Wright brothers were putting pieces of their gliders in a homemade wind tunnel to understand how pieces of the aircraft contributed to the whole before their first powered flight. There aren't many tinkerers in the aircraft world, and many fields are more like aircraft than automobiles.

Anyway, that's my two cents.

Jonny Rochester

03-24-2014, 06:52 PM

Claude,
1. I would like to have the dampers inboard and nearly horizontal but on some slight angles to fit on top of the body, with the rear mount on the front roll hoop, and the rocker fairly high on the side of the car. (Like the FF photo above). Our current CAD chassis has the room. It is better aero, but I am not sure how important that is. Mostly it keeps everything neat, and the dampers are well supported by parts of the chassis we are redesigning anyway.

To have dampers horizontal and low down would mean a pullrod system. And anything mounted low would be external to the chassis as our body is already narrow. The CAD suspension models I have here are done by other students, the vertical shock is to keep everything in the same plane of course. It is an idea proposed by some students.

2. Agreed.

3. I agree it is not best practice to mount things (that carry high force) to the middle of a tube, as it creates bending (or at least a moment to consider). It is also not eloquent to add extra tubes when the design could be tweeked to use a min number of tubes.

Big Bird

03-24-2014, 09:34 PM

Hi Jonny,

Firstly, congrats on getting the UTas unit back together. Great to see one of Oz's early teams making a comeback.

Secondly, full kudos for being strong enough to post your designs up here for all to comment on, and also to present your own opinions. The Australian engineering community needs strong leadership, and as much as I might not agree with some of the things that you might say, I am damn pleased to hear an engineer with an opinion coming through the ranks.

I just wanted to make comment on the front suspension picture shown on the start of the 5th (??) page. I'm going to try to explain some geometry issues with words only, so apologies if this comes across as clumsy.

Your pushrods are two force members, therefore any force transmitted is of known direction (along the tube). The force from the damper unit is aligned along the damper too. What's more, most suspension geometries have A-arm and steering tie-rod orientations such that the pushrod pretty well resists all of the wheels vertical load (e.g. the static weight on each corner of the car). So the pushrod loads, damper loads, and rocker loads (depending on geometry can be quite significant)

Now, a general statement: The further your rocker deviates the pushrod force to direct it into the damper, (i.e. the further the "change of direction" between pushrod and damper unit) the greater the load in the rocker pivot. I'll try to explain this using the letters on my keyboard, which will be fun. The "o" s are rocker pivots, the "v"s represent force directions, the straight lines represent radius arms on the rocker to the points of action of the pushrod and damper forces. The full stops are just spacers , so just ignore then

Firstly, lets imagine a rocker that does not deviate the force "flow" at all - i.e pushrod directly in line with the damper unit

...... v .....
o---- ......
...... ^ .....

Presuming that the the radius arm for the pushrod force and the radius arm for the spring/damper resistance force are the same, force equilibrium tells us that the equal and opposite co-linear forces at the damper and pushrod mounts cancel out, and the force on the pivot is zero

Now, a fairly typical right angle rocker

.>I
...I
...o-----
.........^

Assuming equal moment arms again, a 2d component sum of damper and pushrod forces will show that the resultant force on the pivot is angled at 45 degrees "up and to the right" , and is 1.414 times the input (pushrod) force

Now a complete 180 degree "reversal" as per your suspension design

----o----
^........^

A simple sum of forces in the Y direction (i.e. vertically up the page) indicates the force on the pivot is now 2 times the input force

As mentioned before, most of the vertical load on the tyre is transmitted to the chassis via the pushrod. The forces are significant. Doubling this force at the pivot of the rocker creates a huge load input to the chassis. Directing this force into an unsupported tube in bending creates compliance, and directing this force into an unsupported tube through a moment arm effectively turns the chassis member into a combined torsion spring / leaf spring.

We effectively have five 2-force members transmitting and sharing any "horizontal" forces (i.e. grip forces / road plane) into the chassis (A-arms and toe-links). However we usually have only one link transmitting all the wheel vertical loads (perpendicular to the road plane). On a good day, the "horizontal" grip forces might sum to around 2 times the normal load on the contact patch (with some 3d moment effects amplifying the forces a little). The point I am making is that the load path through the pushrod into the chassis is in my opinion the most significant load path of all - and in fact the whole objective of suspension design is about how we distribute the vertical loads in the tyres to attain balance and grip in the vehicle - yet many chassis designs I see demonstrate significant thought going into making strong node points for the a arm mount points, but then the rocker or shock mounts seem to be an afterthought.

I hope all that makes sense. Keep up the good work Jonny, and the same to your team. And I get the sense that much of what I have written above is known to you, and it is rather basic, but I just wanted to put it in words for the sake of others who might be reading this.

Cheers,

Claude Rouelle

03-24-2014, 09:47 PM

Edward,

Americans think they are the norm, the average.... while in reality on many aspects they are at one end of the spectrum, and that goes for many aspects of life such as service quality and speed, technology, entrepreneurship, healthcare expectation, food quality and quantity etc... It is not right and it is not wrong; it is just different.

I do not deal with German or Italian students or suppliers or customers like I do with Chinese, Indian, Japanese or Brazilian; you can't as they have other habits, other expectations, other self discipline, other work ethics. Once again not necessarily better or worse; just different

What I can tell you is 3 things:
a) You cannot teach in Europe and Asia and to a certain extent in Australia like you teach in the US. One of my good friend was the Noble price of Physics Pierre-Gilles de Gennes (price on work he did about glues) who taught at La Sorbonne in Paris and at the University of Philadelphia; he camel ong before me to the same conclusions; if he taught in the US like he taught in France his class was a mess and vice versa
b) My experience at work and at school (...and my own kids) is that it is better to be strict and demanding from the very beginning and then possibly relax the rules later. If you try to be friend with the people you teach to and then you realize they do not deliver, reversing the course will be much more painful for everybody.
c) In today competitive market, some job interviews are simply nerve racking. FSAE design "interview" is an excellent and still quite gentle training.

That also my 2 cents comments.

Hmm... Do you prefer the front roll center above or under the ground....:)

Jay Lawrence

03-24-2014, 10:22 PM

Jonny,

Why not simplify your front end and run direct actuation? If not, why not move the shock mount to the top of the chassis (and keep your rocker etc.)? This will alleviate the high loadings as discussed above.

Also just an observation regarding the FF layout: in case you're not already, be wary of small lever arm links (toe base, ARB T) as these allow greater combined slop due to compliance stacking (increased loads). From memory, the bad steering cars I drove were something like 80mm toe base, and the good were 120mm or more. Obviously you need more rack travel for larger toe base, but it's worth it. Also be wary of uni-joint usage (especially if you plan to run your rack on the floor unlike the FF), as these are pretty bad for creating more steering slop.

Big Bird

03-24-2014, 10:29 PM

Jay, you beat me to it. I meant to offer the same thoughts regarding direct acting shocks too - but lost the train of thought amongst all the words...

Jonny Rochester

03-25-2014, 02:14 AM

Big Bird,
Thankyou for your detailed description, understood. It reminded me of what I should've known and I used this explanation to push for my own idea of top mounted Formula Ford style shocks. Excellent. We are now designing the angle between pushrod and shock to be a bit greater than 90 degrees (reduces forces at the pivot as you say).

My 2nd personal option is also to have the shocks up the top, inline with the rocker as you suggest.
We have considered direct acting but don't want to do it because we have already bought the shocks and don't think they have a suitable stroke for direct mount.

Jay, (Steering)
I don't know the term toe-base, but at a guess we have a front toe-base (effective steering arm) of 70mm, and 75mm at the rear. I know it is small but I was constrained by a few things. The main thing was wanting to keep the steering rack low without bump-steer and fitting the mounting point inside the wheel etc... And our lecturer was asking us to keep all the upright mounting points the same as on the 2002 car if possible. I think we are ordering the Stiletto rack. Will try 2 uni-joints close together forming a cardan joint up near the steering wheel. I guess we should keep the rockers fairly big for less movement if that's what your getting at?

Jonny Rochester

03-25-2014, 02:45 AM

For everyone commenting here, thankyou for your kind comments and welcome. Some have misunderstood me (partly my own fault).

There is a distinct difference between myself, and the UTAS FSAE team. When I write "I", "I have", "my preference" etc, that is talking about myself, Jonathan Rochester. I am 40 years old, I have a diploma in engineering, I am a qualified mechanic, I have run my own business using a TIG welder and lathe, I built a racecar (sedan/coupe) and I tuned a few racecars (sedans) etc... I have done subjects at uni on and off over many years. And I attended FSAE-A at Werribee and took notes.

When I write "the team", or "students", "some boys" etc, then I am talking about the FSAE team here at UTAS. As a group of people, our opinions and experiences differ. Some of the work I have posted here is from other team members, and maybe I am a bit naughty for doing so.

Consider some constraints. Big business will not sponcer us in Tasmania unless we go electric or hybrid or something "green", it's the current nature of Tasmania. Petrol is done and dusted in peoples minds. With limited people/money we must use as much of the old car as possible just to get a car running. Our lecturer was not involved with the previous car, our pool of expertise has to be built up from scratch.

Now if you go back and read everything I wrote, you may understand.

Jonny Rochester

03-25-2014, 03:03 AM

Americans think they are the norm, the average.... while in reality on many aspects they are at one end of the spectrum,

Correct. However I'm not sure how this relates to engineering, except maybe the metric system and the size a pickup truck needs to be for an individual.

Edward M. Kasprzak

03-25-2014, 05:34 AM

Claude,

The more I learn about cultures beyond my own the more fascinated I am by our collective human race. Broadening one's perspective is always beneficial.

The whole "teachers, not friends" concept is so true. My parents got that one right, and I'm very grateful for it. We have our son on the "strict now, maybe relax later" approach, too. He's only 2, but like in so many things consistency is essential. We'll see how it all turns out.

It's a lifetime of learning!

As for the roll center, I guess it would depend on the situation and what I was trying to acccomplish :-)

Jonny Rochester

03-25-2014, 06:56 AM

Our roll center maybe about 45mm on the front and 55mm at rear. I'm not sure, or sure why this question came up.

Claude Rouelle

03-25-2014, 08:38 AM

Jonny,

The question was purposely out of context; I was trying to be facetious by suddenly asking a engineering question (that can be a huge debate) in a debate which became more philosophical or sociological.

Now that you better explain who you are, things look a bit more understandable (but rudeness still not acceptable). Everybody with good ideas and questions is welcome here and again cudo for exposing "your" car pictures. I just would love to read about your other team members opinion too.

Claude

Jay Lawrence

03-25-2014, 09:08 PM

Hi Jonny,

Yes, by toe base I mean the steering arm length from centre. Your constraints are understandable, but just keep in mind the possibility of a rack/geometry mismatch (driving an enduro with heavy steering is not fun), especially if comparing to FF, which operate at higher speeds with no aero. In my experience the 2 x uni joints is a point of weakness in the steering, as you have 2 x slop and also you can end up putting the column into bending off its intended axis. With the current template rules and given ergonomic concerns, if I were building a FSAE car now it'd be with a vertical steering wheel and bevel drive to rack.

Claude Rouelle

03-25-2014, 09:30 PM

Jay, Yep but a vertical steering wheel is not really ergonomic, I mean not easy to drive. Claude

03-25-2014, 09:34 PM

Jonny,

We have considered direct acting but don't want to do it because we have already bought the shocks and don't think they have a suitable stroke for direct mount.

Well, IMO, the REAL REASON is that you want to do something really complicated, and sophisticated looking, because that's what's on real racecars! Your "already bought" shocks would work fine Direct-Acting, but it seems that you prefer the highest-possible-CG, FF-system, because...?

Since FSAE is supposed to be an educational exercise, why don't you try the "Decision Matrix" approach. These DMs have nothing to do with making actual engineering decisions (they are, for the most part, "pure marketing BS" tools), but you and the other students might have to use them in your future engineering careers, so perhaps time to start practicing...

Start by drawing up column headings for, say; Delta-Mass, Delta-CG-Height, Delta-Manufacturing-Time, Delta-Cost, Delta-Compliance, Delta-Friction, Delta-Aero-Impact, ... etc.

Then add row headings for; Pushrod-and-Vertical-SDs, Pushrod-and-Highest-Possible-SDs, etc... Add a row for Direct-Acting-SDs at the bottom so that it looks like you are actually doing a fair comparison of these.

Then fill the grid with your "engineering judgement call numbers" for the various factors, maybe from 1-10. You should also have some "weighting coefficients", maybe x 1-5, so that you can fudge the results in case they aren't coming out the way you originally intended. Like I said (usually in this industry), these DMs have nothing to do with making RATIONAL, WELL REASONED, decisions.

Finally, add a bottom-most row for Why-Monash-Use-DASDs. (In case you don't know them, Monash have had some limited success in the FSAE-Oz, and some overseas, comps.) Here, your entries in the grid will have to be written out "engineering justifications", or some such.

Perhaps something like:
Delta-Mass - "Monash realize that for aero to work, their car has to be absolutely as light as possible. Therefore, they are prepared to SACRIFICE ALL MECHANICAL GRIP from crap DASDs, in an all-out effort for maximum lightness."
...
Delta-Aero-Impact - "Monash realize that AERO IS A WANK (the cars are too slow to develop any significant aero DF, and their huge wings are there just to fit in all their sponsor's names, the rich bastards!!!). Therefore, they are not the least bit fussed about DASDs messing up the aero flows, and they would rather spend the money they save on pushrods-and-rockers on beer-and-pizza nights...".

Yep, lots of good, rational, well-reasoned, reasons for doing what you wanted to do in the first place! :)
~~~o0o~~~

Oh, and like others above, I am really enjoying this thread. Please keep going with UTas's openness in their design process. I hope all the feedback helps. However, I acknowledge the saying "You can lead a horse to water, but you can't make it drink...".

I look forward to seeing UTas at Oz-2014.

Z

03-25-2014, 09:44 PM

Jay, Yep but a vertical steering wheel is not really ergonomic, I mean not easy to drive. Claude
Claude,

Think about why Jay wants a "bevel drive to rack" with his "vertical steering wheel".
~~~o0o~~~

Jonny,

I would suggest keeping Jay's "vertical steering wheel" to Bevel-Gear-Box (~1:3 ratio), fitting a Pitman arm to the bottom of the BGB's output shaft, and tossing the R&P. Spring-load the BGB's crown-wheel against its pinion to eliminate all backlash. End result is much lower friction, and zero slop, compared with R&P.

Z

Jonny Rochester

03-26-2014, 01:46 AM

Z, I'm not a fan of the Decision Matrix. A friend of a friend decided she may break up with her boyfriend. Being university trained (UTAS economics), she draw up a Decision Matrix, however it was only 2 columns. Reasons to break up/ reasons to stay together. The reasons to break up column was longer so she broke up with that guy, because she forgot to correctly weight each item. It's a massive fudge factor anyway.

I have seen a grid to choose track length of a FSAE car. A list of all know competitors for 2012 where listed, the average of their track width was taken, and that was the decided track width (with extra weight on Monash of course!). (It's a reverse engineering process that works very very well!) lol I now have the extra luxury of seeing cars get on 2 wheels... and hit cones...

I have reasons to use pushrod over direct acting. It's mostly the ability to independently adjust the stroke and spring rate by changing the rocker ratio. The reasons against pushrod (with the shocks up on the body) is because it is a bit hard to design with template rules and the size of FSAE cars, but we have done it today in CAD. I'm not allowed to show you yet but I like it, not because it is complicated, but because it is simple. Our current design happens to be wide track and narrow body, so direct acting shocks is not elegant without bending in the wishbones or funny bracket.

As for the trap your laying of "its what race cars have", well it's not a bad place to start because a bought racecar has 100years of development over what students are designing. As for "it's what Monash do", well, that's exactly the same thing except it's 12 years of (student) development. Monash this Monash that, don't care. Their turbo is the wrong size causing lag.

Jonny Rochester

03-26-2014, 01:55 AM

Jay, I looked into steering then handed that project to someone else. But it was my idea to use the Stileto rack (the light alloy one), and either 2 uni joints forming a cardan joint up the top, OR the rack and 90deg bevel gears at 1:1 ratio. If using the 2 uni joints, I would have a support on the shafts to stop them bending and binding the unis.

We looked at what our old 2002 car has. It is a 90 degree steering box with a pitman arm down the bottom. It is not bevel gears, it's more like steering box with a very low ratio. It's still a possibility I guess. A single uni joint was used for adjustable steering wheel height, so not exactly a vertical steering wheel.

All these components are fairly expensive. We can't just go out and buy everything.

Jonny Rochester

03-26-2014, 06:37 AM

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/UTAS_26-3-14.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/UTAS_26-3-14.jpg.html)

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/1458447_10152115613744667_2124996274_n.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/1458447_10152115613744667_2124996274_n.jpg.html)

This went live on our facebook page today. It's not finished. The front shock position is my idea, so continue to grill me on that personally. A 4th year student spent hours (days) getting this to work in CAD and I think the front end is fairly good (but still needs rack and column and pedals). He has made a triangulated area where the rocker pivot and shock are mounted (which carries high force I know). And it fits within the body, and outside the 350mm square template, and with a pushrod not too long. A fair few requirements to join together in CAD. The rocker is on the back side of the tube, a little unusual. We still haven't designed alot of details, such as the exact rocker post and bearing we are using. Rear suspension and ARB's not yet designed.

I am keen to see a ARB design that would work with this.

The side intrusion area is not finished. The top tubes need to bow out wider. There maybe too many tubes in that still, but feel free to make suggestions on that too (not demeaning questions).

Claude Rouelle

03-26-2014, 08:36 AM

Jonny,

I see chassis polygons with more than 3 sides right where the damper is, ahead and under the damper. Lack of triangulation, not a good thing. Damper mounting on the chassis in the middle of a tube instead of a chassis node (as it is decently designed for the bottom wishbone), not good either.

It seems the front rocker plan is far away from the chassis node. That rocker axis will bend and the rocker itself is single shear. Lots of compliances.

I am sure you can achieve the same chassis (= "big bracket") functions with less tubes (therefore lighter chassis) and still stiffer. Usual good FSAE tubular chassis are in the 25-30 kg zone and still about 1500 Nm/deg (from wheel hub to wheel hib, suspension included but no rim or tires). Just by experience and without any FEA analysis I bet this chassis is heavier and weaker.

The chassis seems big, much bigger than the templates require but that can be a visual illusion. (although there are often bad surprises at technical inspection: students put little thinks like electronic loom or foam for leg shock absorption, seat attachment... and suddenly the car does not pass the tech template test)

I wish we could see steering rack, steering column, upright and your ARBs.

Seems you did improve chassis torsional stiffness in the cockpit area compared to first posts

Again congratulations for having the guts to post this.

Markus

03-26-2014, 09:04 AM

Jonny, you can check FS Team Tallinn 2011 and Metropolia Motorsport (Helsinki) 2011 cars for a couple of ways to do the ARB for a similar setup.

Claude Rouelle

03-26-2014, 11:57 AM

Markus (and all),

Although the cars you mentioned ended up being excellent cars and excellent examples of well thought and well manufactured cars (and quick, well tuned and well driven cars) THAT is THE #1 mistake in design process.

Design your own thing THEN, before you start manufacturing, look at what the others have done and/or ask other persons (including your faculty advisor if you have a good one and/or alumni) what they think of your solutions, not the other way around.

You will learn so much more, you will acquire so much more skills. Make your brain work before you eyes. Use creative thinking.

It could be that somebody in your team has a better idea compared to what already exists. By looking at other cars pictures your miss the opportunity to exploit each of your team members resources, experience and imagination. Your vision goes from 360 to 60 degrees; you miss the opportunity to conceptualize.

Forms follow function, not the other way around.

Make sure you define what your functions (what each and all parts as well as the whole assembly) are supposed to achieve before you start designing (and even worse machining) the forms.

This approach goes not only for concept well defined before CAD; so many people rush to Excel or MatLab without having well defined (in group ideally) what they are looking for and what their equations (and units!!) are.

Markus

03-26-2014, 01:05 PM

Claude,

I completely agree with your thinking, and while I was active member in the team that was the approach most of the team was trying to follow.

"I am keen to see a ARB design that would work with this"
is what I responded to, and maybe my post came out a bit in the wrong way. I didn't want to imply that those were necessarily good solutions nor that you should design a car by copying existing designs... Just wanted to give a couple of examples, as Jonny was keen to see some.

Big Bird

03-26-2014, 05:31 PM

Hi all,

Thanks Jonny for the opportunity to critique your design, or in this case your design process. It is interesting to hear you are 40 years old, I sensed some “above average” worldliness in your earlier posts.

You touched on a pet peeve of mine – the use of CAD as a conceptual design tool. What is wrong with a sketch?

CAD is a finishing tool. It is a lousy conceptual design tool.

CAD is about the precise placement of points, surfaces, components. It takes time to do this. I note that you say that a student spent days preparing that model. By investing that time he, and the team, will feel significant investment in the design. You dont need that investment this early in the concept design. It is actually counterproductive.

During the concept design stage you need to be able to chop, change, move node points, try different tube configurations, try different material ideas. This is the time to BE CREATIVE. And spending days to prepare a concept sketch is counterproductive to the exploratory nature of this part of the process.

I HATE it when I get invited to a “design review” only to be confronted with no visuals and lots of hand-wavy words because “we haven’t finished the CAD yet”. It happens so often I could cry.

SKETCH, people, SKETCH. Rough stuff out. Think pencils, paper. Crayons, napkins. Sticks, dirt. It is valuable exactly because it is, by definition, sketchy. Low investment, high volume, simple throw away visuals to test concepts. Finishing CAD for a concept design is the engineering equivalent of printing and framing your shopping list when you are baking a cake.

Thanks Jonny, this is directed to new engineers in general, not just you

Jonny Rochester

03-26-2014, 08:47 PM

I'm keen for sketches, I have a folder of sketches I carry with me. I find the 4th year guy responsible for brakes, I show him some sketches to bring him up to speed with my own research. I do the same for steering, suspension etc. I find the guy (re)designing chassis and do a sketch of my own ideas. Sometimes they are already in CAD so I make suggestions, a bit higher here, a bit to the left there etc. Often they come to my way of thinking, sometimes I'm out of ideas myself, which is why I'm putting some CAD (our version of a sketch) on this forum. A sketch is much quicker. CAD is used to check interference, and there are a lot of things that could not work in a sketch if the dimensions are too far out. CAD can be very quick with Inventor if you are practiced. (youtube demos of Inventor are mind blowing)

Jonny Rochester

03-26-2014, 08:49 PM

AutoCAD is the precise placement of points. Inventor is flexible, you can design and change the dimensions later.

03-26-2014, 09:06 PM

The side intrusion area is not finished. The top tubes need to bow out wider. There maybe too many tubes in that still, but feel free to make suggestions on that too...

Jonny,

Your first pictures of your built frame had 3 tubes each side in that central SIS area (ie. top, diagonal, and bottom tubes). Assuming that the distance from FRH to MRH is "L", then your built frame had a little more than 3 x L of tubing, each side, in that area.

Your first CAD image added a whole lot more tubes in that area. Lots of verticals and diagonals (many seemingly going nowhere special?). I would guess that you had about 4 x L tubing each side of the SIS area.

Your latest CAD image has added another shoulder height longitudinal tube in that area, plus a few more diagonals, although a bit tidier now. You now have well over 5 x L tubing each side of the SIS area.
~~~o0o~~~

Is there a pattern developing?

Well, IMO, your CADing is giving you a frame that is undoubtedly getting much heavier, and much harder to build (many more nodes, welds, etc.). And it still has the torsional stiffness of a wet noodle. And the "driver egress" is getting a bit harder.

Listen to Geoff, and realize that all this could have been figured out much more quickly and easily by a few sketches on scraps of paper. Or by drawing full-scale frames with chalk lines on the floor. Or, perhaps best yet, by making full-scale models in plywood, or PVC tubing, or with real steel tubes as you did right at the beginning.
~~~o0o~~~

[Mini-Lecture] The failed education system means that most students haven't been taught how to design a frame for torsional stiffness. (And as noted elsewhere, if the frame is torsionally stiff enough, then it (should!) be stiff and strong enough in other modes.) The central section of the frame, namely the bit with the big hole cut in it for the driver, is the section that adds the most flexibility and weakness. It is "the weak link".

The FSAE Rules (ugghhh!) mandate a longitudinal SIS tube at about 300-350 mm above ground (from memory?). So your big decision is whether to make this the topmost side member, or to add another longitudinal tube up higher (say at ~500 mm), still with the mandated tube at ~300 mm.

But, importantly, note that adding that higher tube does NOT necessarily add much torsional stiffness. Sure, it might look as if it does, but if the end bits of the frame are cocked-up, as they usually are in FSAE, then very little extra stiffness.

[Tech-bit->] For a given wall thickness, a tube has its own torsional stiffness (ie. by itself, and not in a "spaceframe") that is proportional to its diameter CUBED. So, double the diameter of the tube and the mass is doubled, but the torsional stiffness is increased eight-fold. Conversely, having two tubes of the original diameter again doubles the mass, but now the combined torsional stiffness is only doubled. [End-Mini-Lecture]
~~~o0o~~~

Summing up the above, most of the torsional stiffness of your frames (real or CAD) comes from the "independent" twisting of the 6 to 10 longitudinal 25 mm diameter tubes (ie. ~3 to ~5 tubes each side).

If you modify your original built frame (page 1) so that the upper SIS tubes are 50 mm diameter (rather than the current ~25 mm), then you have the torsional stiffness of 20 x 25 mm diameter tubes (count 'em), with the mass of 8 x 25 mm tubes. You also have a lot fewer nodes, welds, etc... And if you also shorten the whole car, then even better...

Here is an old 2005 thread with some numbers suggesting that only 1 tube is more than enough - the "44 gallon drum chassis" (http://www.fsae.com/forums/showthread.php?7732-Steel-Frame-Design&p=113807&viewfull=1#post113807). The WWU "Twin-Tube" chassis (page 1 on that thread) is an extreme example of what I am getting at above. It is also a very good idea. Also other useful stuff on that thread...

Z

Jonny Rochester

03-27-2014, 02:30 AM

Z,
Read and understood. The genesis of our chassis actually goes back a few years before my involvement. More on that later...

Our actual built chassis pictured at the top is 30kg. Our current CAD design would put it over that. Maybe when we decide what tubes we need we can delete others. Torsional stiffness is guesswork till we measure something. We are going to twist the actual chassis we got now and see what numbers that gives. We do have FEA of the chassis design completed in 2013, however that design is a bit different.

SIS requires 3 tubes below 350mm which is what we have. Then I would add 1 tube more at shoulder height, which would fix chassis stiffness if in fact that was a problem. The guy doing CAD has added a few more, toying with ideas. Thankfully the guy doing CAD will also be doing the real twist test, plus live data from chassis stress later when we get it going, so he can wear the success or failure of that.

Jonny Rochester

04-05-2014, 06:39 PM

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/Untitled.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/Untitled.jpg.html)

This image is taken from final year honors thesis of A. Walker at UTAS, November 2013. The suspension pictured is from B. Johnston of the same year.

The engine and driveline was no more developed than what you see here, but it came with a full set of workshop drawings for the chassis, so that is what I started to build, as seen in my first post.

I didn't build the side pods, and I have put the engine in the back etc... and we are now working towards a traditional by-the-numbers fsae car.

But was I too harsh? Could we have made the side engine work?

Markus

04-06-2014, 02:49 AM

Anything can be made to work but the picture looks like a solution that is unnecessarily complex and heavy for questionable benefit...

04-06-2014, 11:17 PM

Jonny,

Firstly, I should note that I see "side-winder" cars as UNNATURAL. Certainly, such asymmetrical layouts have not been successful in the Natural world's "survival of the fittest" comp (well, except for very small asymmetries...).

Nevertheless, I reckon the side-winder in your above post would have a better chance of winning FSAE-Oz than the layout you now seem to be heading towards. The main reason is that the side-winder is quite a bit shorter overall, so potentially lighter and with a lot lower Yaw inertia. These, especially the low Yaw inertia, are important performance factors in FSAE conditions, though often overlooked.

By comparison, your built-frame (first post, page 1) has grown half-a-metre at the back, the driver is now too far far forward wrt the wheels, and the two major masses (driver and engine) now form a long, high Yaw-inertia, dumb-bell. You DO NOT WANT a LONG, F.Ford-style car. Very different conditions...

Of course, there are many details on the side-winder image that suggest that it could have become a real cock-up. Briefly, some bad frame detailing, far too many tubes in the sidepod structures (and why two?), engine too far forward (and unnecessarily so), unnecessary layshaft in the final-drive (ie. 2 x chains), and more...

To finish on a positive note, I suggest that with your current car you aim for the same overall frame length as the side-winder image (if not shorter), same relative location of wheels and driver, and then try to squeeze your engine into that space just behind the driver's back. I reckon it will fit with the diff a bit behind the rear-axle line (drive-shafts swept forward-to-wheels). You already have the built-frame, so put the driver and engine in it to see how neatly it can all be packaged.

And keep tidying up the frame. And keep adding more simplicity (eg. direct-acting SDs, +++).

It could end up a good car...

Z

Jay Lawrence

04-06-2014, 11:42 PM

Jonny,

Deakin university have run a sidewinder for quite a while. They don't seem to turn up at every comp and rarely finish high up the order when they do, but their concept is very nice (they run/ran a KTM520EXC engine I think). May be worth contacting them if you intend to continue with the concept.

Jonny Rochester

04-07-2014, 02:30 AM

For the side engine design, the drivers cell was designed as narrow as possible per the rules. It was thought the left sidepod would be used for "everything else" like battery and radiator, which would balance the weight. Looking at this again later, we didn't think it would actually balance, one reason why we chose rear engine. The side engine was chosen for a short wheelbase, however there is a min wheelbase in the rules of 1525mm, and many teams are close to that with a rear engine. With our current designs our wheelbase is closer to 1650mm but without any testing it's not something I can comment on. I suspect some FSAE cars are a bit twitchy at top speed so some extra length may help with that.

Jonny Rochester

04-08-2014, 05:38 AM

https://scontent-a-nrt.xx.fbcdn.net/hphotos-ash3/t1.0-9/10153273_270885073085752_2013851945887983443_n.png

Thijs

04-08-2014, 06:37 AM

I suspect some FSAE cars are a bit twitchy at top speed so some extra length may help with that.

What sort of speeds are you hoping to achieve?
btw, superkarts can reach up to 250km/h. Their wheelbase needs to be below 1270mm according to the rules (and greater than 1000mm).

Jonny Rochester

04-09-2014, 01:22 AM

This most recent graphic is stolen from our own facebook page. I can now say I am proud of this. There are little pieces of my own design in it. More of the design is now from current members which helps moral. Still some remnants of design from past years, and some parts not designed at all.

Question: The roll hoop brace will probably change, as someone told us it is not triangulated down to the bottom of the chassis. As the driveline box is not triangulated. But then we thought, even on our chassis as pictured at the top of this thread my not pass that rule either? As we had a V section up the back, not big diagonals... ?

04-09-2014, 06:29 AM

Jonny,

Frame is still too long.....

The part of the side-winder frame from MRH back is all you need. So in your latest image the MRH braces can end at the rockers (but get rid of the pushrods&rockers, and go direct-acting! :)).

The diagonal brace from half-way up the MRH-brace currently does nothing.

The "V-shaped" bracing behind MRH of the side-winder is OK. A single diagonal for "proper triangulation" might be better. But depends on other small details, like engine-mounts, etc.

"You can take a horse to water, but..."

Z

Jonny Rochester

04-09-2014, 07:42 AM

I can't see how to make the car shorter. I know it's possible to eliminate our rear box, but the driveline would still hang out the back, and the wishbones would have to sweep forward. The wheelbase and length of the car would still be the same. We can't shorten the driver cell, that has to fit legs of a 6' person. Can't shorten the chain, it's already almost too short. We could shorten the wheelbase a little to 1525mm, but for what purpose?

To go direct acting shocks, we would need to modify our (new) shocks in some way, because they are designed to pivot. With direct acting you need one end to be fixed, not pinned.

Jonny Rochester

04-09-2014, 08:29 AM

Here is a clearer view of our chassis. Chassis designer is getting close to locking this in. The rear rocker posts would be right on the node as pictured here, the rear shocks would mount back towards the roll hoop, however still in the middle of a tube. (But facing toward a node). The front rocker posts are on the underside of a tube.

Jonny Rochester

04-09-2014, 08:32 AM

actually, this

https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-frc3/t1.0-9/1463254_10152144519694667_8215870929596285837_n.jp g

04-09-2014, 09:59 PM

Jonny (and other new FSAEers),

Geoff (Big Bird) has a very helpful thread "stickied" at the top of the main section of the Forum. Many experienced FSAEers consider this "Reasoning your way through the FSAE design process." to be compulsory reading for all new, or less experienced, Teams.

Have all of your key Team members read it? Have you all spent a lot of time discussing it?

Judging by some of your Team's recent design decisions above, I think not.

The important point here is that if you don't get the high-level, big-picture, decisions correct at the beginning of the year, then you have Buckley's chance of doing really well at the end of the year.

Sure, if you start with a bad overall design, but nevertheless get all the little details right, then you should be able to finish all dynamic events and beat half the other teams. So you end up mid-field (in Oz that means ~10th of the losers). That is, unless you cocked-up just one of the details, in which case you drop to the back of the grid.

One of the key messages I see in Geoff's "Reasoning..." thread is that a good, objective, appraisal of FSAE tells you that there are a whole lot of things that your car DOES NOT NEED. Geoff's RMIT team eventually proved one of those things by showing that "high-horsepower" was NOT very important in FSAE. Your previous members who chose the single-cylinder engine may have also seen this. Or maybe they were just copying Monash, et al?

Anyway, here are just a few of the other things that your car DOES NOT NEED (or better put, IT SHOULD NOT HAVE):
1. Excessive length. An F1 car with 3.2 m wheelbase (quite typical) will have to do three-point turns at any hairpins, and will be thrashed by a go-kart.
2. Excessive Yaw-inertia. This is very important, but seemingly ignored by most Teams, bar the best (use Search on this Forum).
3. Excessive junk. This is all that stuff that takes time and money to design/build/develop, but doesn't really make the car any faster (eg. pushrods and rockers, see below), so it takes time away from testing.
~o0o~

Getting back to specifics. You want a compact car, with all major masses (= driver + engine) centralised. I would suggest aiming for 40F:60R weight distribution. (BTW, this allows you to have a simple open-diff with no problems, and diff choice is a BIG decision.) Wheelbase = 1530 - 1600 mm is a good range. Too short and you might not get through scrutineering (1520 mm? Oops, build cock-up!). Too long and Yaw-inertia climbs...

Even more specifically, get rid of that rear frame box (the jacking bar structure can be a tiny little thing that bolts to back of diff-mounts). Greatly reduce the size of the front-bulkhead. Remember that the Rules mandate a (heavy!) 1.6 mm steel plate covering most of the front-bulkhead (check Rules!).

Realise that the suspension structure must transmit the forces between the four wheels and the major masses of the car. Since the major masses should be centralised, any suspension structure should "radiate" out from car-centre. Conveniently, this means that some of your suspension-to-frame-mounts can be at the mandated Front-RH and Main-RH.

Direct-Acting-Spring-Dampers need a ball-joint at each end (cf. "... you need one end to be fixed, not pinned." Huh???). You can modify your current SDs to any length you like by making a short "pushrod-like" extension that screws onto the damper shaft (ie. it replaces the thingy that is now on the end of your damper shaft). The frame-end of any DASD should be at a reasonably strong node, again preferably pointing to car-centre.
~o0o~

But, once again, you should read the "Reasoning..." thread, and then ask yourselves if any of the above actually makes sense. :)

Z

(PS. Any engine-guys want to comment on UTAS's plenum and intake pipe? Mbirt?)

Jay Lawrence

04-09-2014, 10:51 PM

Jonny,

There's nothing wrong with having swept A-arms. Many teams do and they usually have a very nice and compact rear end.

As for the plenum/intake: it looks pretty damn long and you may find that this hurts throttle response. Also just be aware that the shape of your plenum is more susceptible to closed throttle vacuum deformation than, say, a spherical one.

Just as a time saver if you haven't got something sorted already: check out AT Power in the UK; they make a FSAE spec throttle/restrictor combination that works very well and is pretty sexy too.

Jonny Rochester

04-10-2014, 04:43 AM

Not my area, but intake length will be looked at very closely...

Z,
It seams you have built a few of these cars before. Where did you study, and will your uni be competing this year?

Generally the students would not be on this forum much (got real uni work to do which is more important), and we don't know who Geoff is. But I did hear him commentate a bit at Werribee when the wind was in the right direction.

However we did get Mark Dutton from Redbull Racing Australia (888) to come and talk to us. He gave good general non-specific advice about this project. He talked about designing parts, doing lots of chassis iterations in CAD, putting in the hours, importance of presentation, taking care with good welds etc.

04-10-2014, 08:23 PM

Jonny,

I haven't competed in FSAE before, and the Uni I went to 35+ years ago is a perennial loser in FSAE today (how the mighty have fallen! :(). I have built other stuff, some of it mentioned on these pages, but that is not the point.

My main point, and Geoff's in his "Reasoning..." thread, is that you CANNOT WIN by following the crowd! If you want to do really well in FSAE, rather than just "being there", then you really have to THINK FOR YOURSELF. Don't take mine, or Geoff's, or anyone else's advice unquestioningly.

Instead, do the calculations, and FOLLOW THE NUMBERS.

Your last-year's team members might have been doing this when they conceived the side-winder. I know you were joking when you started this thread in an "Indian" way, but I am now beginning to suspect that at the end of the year you will turn up with an "Indian car".

"Yes Sir, we have built the finest Mini-F1 car ever to compete in FSAE!".

Z

Jonny Rochester

04-11-2014, 05:14 AM

Z,
It is unrealistic to expect to win in our first year. We aim for a high result by doing things well. Just "being there" would be a huge thing. Last years team was 2 or 3 people. Have you ever committed to a huge project, then shipped everything to Tasmania or NZ to compete at a unknown event? Probably not? That is what it would be like. We don't sit back and yawn thinking about the last 10 years we placed in the top ten and go over the rules again to see where we can find a winning edge. We go over the rules just to build an eligible car. We have a large team now after some promotional stuff, however the new guys don't yet know they'll have to read the rules. If we do turn up, it maybe as an "Indian" team, whatever that means to you. It won't be with a mini F1 car, it will be with a FSAE car, and it would be a big achievement to build a car.

It won't be overly long, it will be about the same length as the other cars as dictated by the rules, packaging and getting an actual person in it. I don't think having direct acting or rockers is going to effect the result, but I have reasons for the way we are going. I started this thread so people can help us if we are going too far off course early on.

But I am not bringing our team down, I know some parts of the car will be very well designed and made. And there will be at least 1 aspect I know of that is innovative and has not been done in FSAE very much. Then again, there are some parts of our car still not designed because we don't have enough strong designers to simultaneously design every aspect of the car. Some things will have to wait regardless of ideal time frames.

Maybe next year I will write my own article about all this. I think there are some things BigBird left out. I would probably list the issues around students having very limited workshop or practical experience if they didn't pull things apart at home. Like you, I have my own pet peeves. I get upset when someone comes into the workshop and asks what the radius of something is. It's almost impossible to measure the radius of anything, we use diameter in the workshop. And I have lots of issues like this... There is no drag net to check that students know the difference between a nut and a bolt. Or if given a spanner, would they know which way to turn it? Is it possible someone could graduate (in mechanical engineering) without knowing 1" = 25.4mm? I could go on...

Mbirt

04-11-2014, 04:45 PM

https://scontent-a-nrt.xx.fbcdn.net/hphotos-ash3/t1.0-9/10153273_270885073085752_2013851945887983443_n.png I would definitely advise that the intake tract runner length design target be established soon because the current design severely impacts packaging for the plenum and other components in the rear of the car. I suggest that your engine guy/team does a quick review of organ pipe theory and reads the writings of G.P. Blair and others concerning empiricism in engine airflow geometry design. The current intake runner is extremely long. It looks like some competitive benchmarking was done for intake plenum volume, however, because the academic mistake of sizing the plenum to x times engine displacement instead of what the engine needs was avoided. It appears to be a bit large right now, it is worth simulating and/or testing smaller volumes if you have the means. Starting at 2 l and working up until a volume of diminishing returns is reached would be a worthwhile exercise. I'll echo the previous statement that the AT-Power bellmouth-throttle-restrictor-diffuser is a great choice for a new team. It should not need further diffusing after its flange at this power level with sufficient plenum volume, so it could attach to the plenum's outer surface. Design the plenum body as stiff as possible--oilcanning from the engine's vacuum pulses will quickly fail an aluminum/RP/CFRP plenum.

I like what I see with the muffler--keep it large in volume because future noise rule changes will not be friendly to singles. An adjustable tailpipe angle will help you strike the best balance of pointing your sound waves away from the microphone and what the tech judges perceive to be legal at each competition you attend. The headpipe from the exhaust port to the muffler that we cannot see should theoretically be designed in conjunction with the intake tract to achieve a desired torque curve. More points are certainly available in the engine calibration and intake design before really fine-tuning the exhaust, however.

04-13-2014, 08:17 PM

It is unrealistic to expect to win in our first year.

Jonny,

Why? You are only up against school kids. :)
~o0o~

... I started this thread so people can help us if we are going too far off course early on...

And that is what most of us here are trying to do.

My belief is that most team's biggest mistake is that they, like you, think that FSAE is hard to win. So, regardless of whether they are a new or experienced team, they try to build something that is much more complicated than necessary. This unnecessary overcomplication of a simple problem then becomes the team's biggest problem. Unfinished car, lack of sufficient testing, etc., etc.

When I first saw FSAE some 15 years ago, and the type of cars racing in it, I did some quick calculations and concluded that there was a massive "opportunity" here. A very simple car could easily thrash the opposition. So, potentially a lot of FUN for someone. There have been some small steps by some teams in that direction. But there is still a massive opportunity on offer.
~o0o~

As an example, consider the newbie Canterbury (NZ) team from last year. Their overall goal was to design a "conservative car, with attention to detail". They certainly executed the "attention to detail" part right, and got 12th overall, out of 23 teams, with 9 of the 11 teams behind them DNFing in Enduro.

Unfortunately (IMO), they chose the wrong starting point for "conservative car". It was not quite a "Mini-F1" car, but it was close to a "Short-Wheel-Base Formula-Ford". This meant there was a lot of (unnecessary!) designing and building for the fairly small 13 member team, so less time for testing and development. Also, the shortening of the "FF" cockpit made the ergo very bad, so hard to drive fast.

I reckon if they started instead with a plan to build a "Long-Wheel-Base Go-Kart", with just enough extras to comply with the FSAE Rules, and with the same "attention to detail", then they would have been looking at top 6 overall, and possibly a few podiums as well. Add a good aero-undertray the next year, and a whole lot more testing and development, and outright wins are there for the taking...
~o0o~

A final example (for a while... :)) is your current engine intake. To me it looks like your engine guy has decided that low-down torque is very important (true-ish...), so a very long intake pipe. He also seems to think that high-revs power needs to be "optimised", so a very large plenum. So, all up, a very cumbersome intake system, possibly TOO COMPLICATED.

Pay attention to what Mbirt says (also on other engine threads), look at what other single-cylinder teams have been successful with, and only fit as much as is ABSOLUTELY NECESSARY. There are much more important performance factors in FSAE than an "optimised (*)" engine.

Z

(* Get your engine guy to read the "Reasoning..." thread to understand why "optimisation" is NOT always a good thing...)

onemaniac

04-15-2014, 12:03 PM

...Is it possible someone could graduate (in mechanical engineering) without knowing 1" = 25.4mm? I could go on...

Today at work, one guy (graduated with a Master's degree in Mechanical Engineering from U of Toronto) actually didn't know how to convert from mm to inch.

So it is possible :D

Big Bird

04-17-2014, 03:21 AM

Gday Jonny,
Great thread you have got going here. And thanks Z for the recommendations re the "Reasoning.." thread.

I note the "we can't win because we are newbies" theme appearing a bit. In every perceived shortcoming there is an opportunity, if you are willing to search for it. I would say our most successful teams were newbie teams, and some of our least successful were brimming with experience. Why? The novice teams would look at things objectively, and respected leadership. The experienced teams "knew it all already", and resented leadership...

Cheers all,

Geoff

murpia

04-17-2014, 07:53 AM

Today at work, one guy (graduated with a Master's degree in Mechanical Engineering from U of Toronto) actually didn't know how to convert from mm to inch.

So it is possible :D
Not a problem, only 2 countries in the world don't work in metric.

Not knowing how to convert from inch to mm? Now, that's a problem... :)

Regards, Ian

Jonny Rochester

04-17-2014, 09:37 PM

Geoff,

I see you have visited many places, Uni YYY etc. However I don't see UTAS on the list! I'm not sure of your official capacity, but you would be invited to come and advise us in Tasmania. Flights to Hobart are very cheap, it's really not that far.

As for the top down physiological stuff, that only works if you already have a team familiar with nuts and bolts and welding, machining etc. and the knowhow to build whatever you design. I know the practical stuff does not have to be part of our degree, and I know students are very smart and will learn this stuff quickly. But not quick enough for a first year team to win.

Our faculty adviser has not yet read the FSAE rules (may not have to?) and is not familiar with bits and pieces you need to buy for a racecar. That is all up to the students, but it is a very big job.

Also, some students are still using the word wheel and tyre interchangeably. Students may know the difference between diameter and radius in an exam, but in casual speech they get it mixed up which makes things very confusing. eg. Students ask me what the radius of the wheels are. I ask them what bit of the wheel they are after. It turns out they want the outside tyre size. I show them the tyre and that it has a 20 on it meaning 20 inch diameter. The word "inch" draws a blank. So working with that we have a long way to go.

But our chassis design has come a long way. It is an impressive CAD model that is purposefully designed, and we have the skills to build it. Design freeze has been announced. Some wishbones are built. The engine runs on a stand.

Jonny Rochester

04-17-2014, 10:08 PM

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/utas14apr.png (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/utas14apr.png.html)

This was our assembly from a week ago. It's changed a tiny bit since, and I have had to sensor some parts. Under that skin is a chassis that should fit everything. For parts not fully designed, we at least have a mockup CAD model showing the overall sizes.

Loz

04-17-2014, 11:22 PM

As for the top down physiological stuff, that only works if you already have a team familiar with nuts and bolts and welding, machining etc. and the knowhow to build whatever you design. I know the practical stuff does not have to be part of our degree, and I know students are very smart and will learn this stuff quickly. But not quick enough for a first year team to win.

Unfortunately Jonny, you have got the rationale behind a top down approach completely the wrong way around. The fact that a group is unfamiliar with a system and lacks expertise/knowledge in most of the areas required to be successful is precisely the reason that a top down approach is needed.

To successfully synthesize a car from the ground up requires a high level of expertise, understanding of the end point and a-priori knowledge otherwise it is likely to be little more than a large collection of components that are joined together in a similar spacial location without necessarily having any real connectivity with the other components in the system. It is near impossible to successfully manage all of the system interfaces in a bottom up build unless there is a high level of expertise embedded in the engineering decision making.

Starting at the top with an approach that seeks to first define the problem, prior to defining a vehicle function and set of constraints without the restrictions that detailed design provides, is not just some system-engineering mumbo-jumbo approach, but is the essence of mechanical engineering (or any high level problem solving for that matter). Not to mention that approaching the project in this fashion is probably the only way to "make everything as simple as possible, but no simpler" (some clever guy said that..).

A trial and error approach is not engineering, it's gambling.

Jonny Rochester

04-18-2014, 01:57 AM

I am not against the top down design, we need it. That is engineering. I am just saying that nothing will be built with only a top down approach, that does not meet bottom up expertise. That is also engineering.

Top down design finds shear force in a joint and requires a fastening pin of radius 6.326mm in mild steel. Bottom up meets that with a 14mm hi-ten bolt for $1.20.

Loz, perhaps you are trying to say, get everything in a CAD assembly before you start making stuff? Our latest image suggests we are not far off it.

onemaniac

04-18-2014, 03:58 PM

get everything in a CAD assembly before you start making stuff? Our latest image suggests we are not far off it.

Jonny, your latest image suggests you're quite far off it.
I will share one example from my very own experience leading a rookie team.

My team is a relatively new team as well (built only 1 car so far) and we had just as much as what you have in CAD when we started welding the chassis. Soon after, we ran into trouble after trouble while designing the remainder of the car on the fly.

The switches, electronics, brake line routing, cooling, fuel tank, filler neck position, all bits of plumbing, shifter linkage, various cable mounts, intake bracket, steering column mounts and mounting points, various tabs, brake lights, catch cans, sprocket guards and more importantly, accessibility as well as fastener and tool clearances... the list goes on.

I cannot recall how many times we realized something can't be assembled in real life or move things around because we forgot something.

Re-working certain parts over and over wasted so much of our time. At one point I could tell the core members were getting exhausted and team morale dropped significantly.

We somehow got the car finished just on time, but we had no time to test it. There was a problem with the ECU so the engine didn't run properly and of course, we fixed it after the competition. It was too late.

You really have to have everything in CAD. Everything.

It includes all the plumbing hardware, brackets, tabs etc plus all the correct nuts, bolts, clips and washers required for assembly and every assembly procedure must be simulated in CAD, to avoid any surprises.

Learning in CAD is much cheaper than grinding off a wrong bracket after it's already welded.

Joe

Jonny Rochester

04-18-2014, 04:19 PM

http://www.cabletiefan.co.uk/cableties/cable_tie_.JPG

04-18-2014, 08:37 PM

Top down design finds shear force in a joint and requires a fastening pin of radius 6.326mm in mild steel. Bottom up meets that with a 14mm hi-ten bolt for $1.20.

Jonny,

NO, NO, NO, no, no, nooooo!!!!!

Very disappointing. But now it is clearer why you are heading in the direction you are.

Another missed opportunity. :(

(Geoff, I can sense your frustration, and I feel your pain...)
~~~~~o0o~~~~~

Joe (Onemaniac),

Man went to the Moon in rocketships designed with NO CAD at all.

Nowadays, large teams of student engineers spend a whole year designing a tiny little car in CAD, then at the end of the year half of said cars CANNOT drive 30 kilometres.

By and large, the CAD, CAE, FEA, CFD, etc., experiments have proved to be an utter failure.

(Example: Compare pre-CAD Lockheed SR-71 and MiG-25, with post-CAD F35-JSF.)

Z

Loz

04-18-2014, 09:53 PM

Loz, perhaps you are trying to say, get everything in a CAD assembly before you start making stuff? Our latest image suggests we are not far off it.

No not saying that at all.

CAD tools are merely a way of documenting a thought process and conveying that idea to others in an efficient and accurate manner that is easy to reproduce and/or modify. Some of these tools also happen to have other built in mechanisms that can be used to improve efficiency by not having to do lengthy (and sometimes implausible) calculations by hand (e.g. FEA, CFD,...).

Yes, having a COMPLETE set of documented ideas is a prerequisite for commencing a build (they could be CAD, drawing board, envelope sketches, toilet door, or whatever else). BUT, only if they have been developed after the problem has been defined, rationalised and an appropriate solution developed. Sometimes CAE tools can be used as part of the problem solving process but they are not a substitute for engineering thought and analysis (which are typically independent of computers and in most cases involve pen and paper).

Put simply, getting everything into a CAD model is of little value if the leg work has not been done to reach a point that you know a-priori what it is you are going to model. Most of this a-priori knowledge is independent of detail design, which for the most part is what a CAD model documents.

onemaniac

04-19-2014, 09:50 PM

Jonny,

Joe (Onemaniac),

Man went to the Moon in rocketships designed with NO CAD at all.

Nowadays, large teams of student engineers spend a whole year designing a tiny little car in CAD, then at the end of the year half of said cars CANNOT drive 30 kilometres.

By and large, the CAD, CAE, FEA, CFD, etc., experiments have proved to be an utter failure.

(Example: Compare pre-CAD Lockheed SR-71 and MiG-25, with post-CAD F35-JSF.)

Z

Eeek. I meant having a complete set of design documentation before fabrication.

It sure can be hand drawings or writing with sketches if it makes sense.

I agree CAD isn't for 'design'. As checking tools, they're pretty awesome.

I insist that full CAD model (or detailed hand drawing, your choice) of the final design is still very important

Joe

MCoach

04-20-2014, 01:09 AM

The switches, electronics, brake line routing, cooling, fuel tank, filler neck position, all bits of plumbing, shifter linkage, various cable mounts, intake bracket, steering column mounts and mounting points, various tabs, brake lights, catch cans, sprocket guards and more importantly, accessibility as well as fastener and tool clearances... the list goes on.

I cannot recall how many times we realized something can't be assembled in real life or move things around because we forgot something.

You really have to have everything in CAD. Everything.

It includes all the plumbing hardware, brackets, tabs etc plus all the correct nuts, bolts, clips and washers required for assembly and every assembly procedure must be simulated in CAD, to avoid any surprises.

Learning in CAD is much cheaper than grinding off a wrong bracket after it's already welded.

Joe

Coming from a team that is not very large, I've worked on building a database of models of sensors, sprockets, engines, driver model, hardware, etc, etc, etc. It's helpful to give some random parts to new people on the team that need the experience modeling and have models on hand to drop into anything later like wheel speed sensors or some goofy filter thing that the powertrain team has been requested. It means that when I've advanced past scrolling ideas in my mind and sketches I can drop a few parts into space to check for clearances and a sanity check. But everything in CAD? only if you are packaging down to the very last millimeter, and that is rare to see. This year's car was largely influenced by me and I focused on 3 things: efficiency of materials, simplified packaging, and knowledge of the design and build process to bring a brand new idea from sparks in the brain to a living, breathing, driving, competitive car. It would be helpful on the design front to have knowledge of exactly what component is where and how to get around it, however it's a waste of time to chase people to get everything in CAD, you can spend just as long verifying some small 'proof of concept' projects and playing around with some PVC pipes and whatever other scraps you've got. Honestly, counting right now I have 898 parts in our 2014 assembly model, not a ton, but enough to tell me that some of the largest clearances to expect in our outboard design is about 0.075" between components and a CAD weight of 321 lbs without driver, which just means I'm missing a few things like wires and some coolant hose.

Get a concept together before touching CAD. Get it on paper, 600cc engine, 400lbs, CG height of 12", whatever on and on.
Build to that.....quickly. Even with as many parts as I have in the model, most of it is just packaging, the car has already been built once out of cardboard, plywood, and validated to be a concept that is achievable.

Johnny, as has been said in the stickied sections, bottom up design is a horrible way to go about it. Do you have some concept of what you're building? Bottom up is how you end up with cars that have 3 wheels and no identity of the goal they are trying to accomplish or a car that only works when driven in reverse. Top down is a way of life. Anything else is just masturbation and tinkering.

Now, go get rid of those 14mm bolts, I don't think we have a single fastener on our car that large. :p

Big Bird

04-20-2014, 02:27 AM

Hiya Jonny, hi all,

I can see where you are coming from Jonny. Universities are full of impractical academics who see inefficiencies in having to use an M6 bolt when their calculations say that they really need an M5.2375 bolt with a 0.8765mm thread. And they think that collectively, if the whole world came together to solve all the little problems then suddenly we would have world peace, we would never run out of food , or fuel, or forests, etc etc. Glad to see you are not one of them.
If you don’t mind I’ll pitch in a few words. I’ll recycle my MasterChef analogy if I might, or at least the cooking theme behind it.

Top down design is about following the below path:
- Understanding your purpose
- Understanding your capabilities
- Understanding your design problem
- Proposing a solution
- Delivering on that solution

For the sake of the argument, I’ll say my purpose is “impress a girl”, (or a guy,if that is your thing). The project brief is “My housemate’s sister is coming around tonight to have dinner with us. I reckon she is cute and want to impress her”.

The top down designer knows the purpose, the reason for doing something. The top down designer’s process of design might look like the following:

Top level Purpose: Impress Bob’s sister
Initial thoughts / possibilities: make her laugh, write her a song, cook something, paint her portrait, wear a Hugo Boss suit, strip down to a g-string and show her how many one-armed pushups I can do
Acquired knowledge/ understanding: she is a bit of a socialist so Hugo Boss won’t work. I can only do one one-armed pushup, and I can’t sing. Of the remaining options, I reckon the most practical option is to cook something.
Decision: cook her something nice

Next level down:
Problem – what to cook?
Context – I’ve got a decent oven and about thirty minutes to prepare. Has to be ready to serve in three hours time. I don’t want to undershoot and just serve up boiled beans. I don’t want to aim too high and fail delivery. Bob says he is going to do main course. He says his sister loves chocolate.
Decision: I’ll bake a chocolate cake

Next level down:
Product – what kind of chocolate cake?
Context – Packet mixes are horrible. I have a chocolate cheesecake recipe, but no cream cheese. Chocolate ice cream cakes are great, but I can’t get one for under $30 and that is over budget. Mum has this cool never-fail chocolate cake recipe, and I’ve got all the ingredients in the fridge.
Decision – make mum’s never fail chocolate cake recipe

Next level down :
Parts – what are the details of the final product?
I’ll make the basic cake recipe, and fill it with cream and cherries, like a black forest cake. I can serve it on the big glass cake stand that mum gave to me last year. It needs to be out of the oven by 5pm so it has time to cool before I put on the chocolate icing. I have a nice dessert wine we can have with it. I can duck down to the shop to buy some icecream to serve with it while it is cooking.

Note how we work down through the hierarchy to achieve our final decision? The reasons for each decision are distilled down from above, and the details of “how to do it” at each stage are further down the hierarchy. By understanding the decisions you have made at each stage, you are empowered to make changes where necessary and understand how each change will impact on the overall goal.

Now the bottom-up “Designer” might work something like this
Top level purpose – impress Bob’s sister
Implementation – I’ll bake her a chocolate cake. The guy who won her heart last year made her a chocolate cake. Girls love chocolate cake. Where is the cake recipe?? What do I have to do?

Observations:
Top down design is along the lines of “to impress my housemate’s sister, I could make her a chocolate cake”.
Bottom up design is more along the lines of “the way to impress a housemate’s sister is to make her a chocolate cake”

The former is about choice. It is about being open minded, it is about understanding context, constraints, your own capabilities and resources to deliver a successful outcome. It encompasses creativity, flexibility, and being focussed on the purpose. It teaches you how to be a problem solver, about how to come up with different solutions for different problems, and even how to approach novel problems that haven’t been solved previously. It is about understanding first principles, basics – that with an understanding of how people can be impressed, we can create many different ways to impress a girl / guy – that by understanding humour, we can create our own jokes – that with an understanding of how to bake, we can create a chocolate cake, or a croissant, or biscuits. It is about understanding the context of the problem, and therefore deeply understanding the priorities.

The latter is about wanting to know what the answer is. It is about looking for a recipe rather than understanding the context, it is about looking for a book entitled “how to impress a housemate’s sister”. It is about being a one trick pony with a chocolate cake recipe. It is about believing you will win by doing the same thing as everyone else but you will somehow do it better.

The top down designer’s approach is flexible, and can adapt to “roadblocks”. Oven packed itself in? Cool, I can cook something else, or I can write that song, or work on that comedy routine. The bottom up designer wonders how to make that chocolate cake without an oven.

FSAE is exactly the same problem. We have people coming around at a given time, and we want to impress them – this time with engineering skills rather than our culinary prowess. We have a time constraints, budget constraints, our own particular skillsets and interpretation of the problem.

Unfortunately, these people we are trying to impress have been served so many metaphorical chocolate cakes that they all taste the same. They are dying for you to tell them something unique and creative about how your mind works and how you might impress a potential partner – but the answers they hear are all about what you did when you made your cake.

We have all sorts of weird logic being sprouted in this community, primarily because the method of enquiry is based on correlation rather than causation. We have nations metaphorically arguing that it is really hard to impress girls /guys in their country because they don’t have access to the same flour as we do. We have universities that fail repeatedly year after year to fail to tell a single joke or make a simple ham sandwich or hum a few simple bars of a song – because they “know” that the way to impress Bob’s sister is chocolate cake, and that their cake made with imported Belgian chocolate and Icelandic yak’s milk and baked through a special collaboration between four sandstone universities in the NASA synchrotron is going to be so much better than Monash’s. Next year. We had some problems this year. Suppliers…

Jonny, the fact that you have a novice team means you have the perfect ingredients for a unique take on how to impress all at FSAE. You are telling us that your team won’t win because they haven’t done their time making chocolate cake yet. I’m telling you that if we get in now, you can use your own unique local ingredients and knowhow and make a bloody good apple pie from first principles..

Sorry about the essay mate, hope it makes sense. Good luck with it all, and keep up the good work!

Geoff

p.s. Bob’s sister is SO sick of chocolate cake these days…

Kirk Feldkamp

04-20-2014, 12:26 PM

By and large, the CAD, CAE, FEA, CFD, etc., experiments have proved to be an utter failure.

(Example: Compare pre-CAD Lockheed SR-71 and MiG-25, with post-CAD F35-JSF.)

Z

Haha. Boy, talk about making big leaps in a logical argument. Correlation versus causation... anyone, anyone? There were thousands of reasons those programs were different and ended up differently. Military programs are such a fustercluck that you'd be really hard pressed to blame any one factor for perceived success/failure. ;)

-Kirk

04-20-2014, 09:57 PM

Haha. Boy, talk about making big leaps in a logical argument. Correlation versus causation... anyone, anyone?

Kirk,

You are entirely correct. In my defence I did say "by and large...", and I only gave those planes as examples, not as a logical proof.

But I do stand by my assertion that nothing that has been done in the last 30 odd "CAD years" could not have been done equally well, and in probably half the time, in pre-CAD times. If anyone disagrees, then please give examples!

In fact, looking at mediaeval cathedrals vs modern shopping-malls (socially, the same thing), I see NO progress at all. More steel allows greater heights, and the heat-engine allows faster build-time, but design-wise we are going backward. There really is some atrocious structural design in modern (CADed) civil engineering.

Furthermore, in the FSAE arena a complete documentation package (by CAD or hand), as suggested by Joe and others above, is absolutely NOT NECESSARY. A simple little, ONE-OFF, prototype FSAE car, that will require significant modification during testing if it is to have any chance of doing well, does not need any drawings at all.

Forget about CAD entirely. Do a few hand-drawn concept sketches to get started. Then build->test->modify the car "in the round". It is about how fast your car is in the Dynamic events that counts, not how pretty your documentation is.

Z

04-20-2014, 10:06 PM

But back to the more interesting stuff... :)
~o0o~

Geoff, THANK YOU for introducing me to Bob's sister! She's hot!!!

Now, I know that at Bob's upcoming soiree there are going to be umpteen, clever, University-educated, young men trying to woo Bob's sister. And I have heard that they will all try to impress her by baking chocolate cakes and the like. So what can I do?

Thinking ... thinking ... I need an advantage ...
Think harder, dammit! ... Must go back to first principles ... the fundamentals ... grrrrrrr...

Yes, I know! I'll consult the ancients. They knew a thing or two about this stuff ...

Yep, here in "Ye Olde Booke of Classicale Matings." it says;

"Axiom 1.
Roses and chocolate will turn a girl's head,
but liquor is quicker to get her to b..."

(Well, you guys can look it up.)

Now, how can I turn this fundamental principle into a workable plan? More thinking ...

Ok, given that this soiree is happening in the Apple Isle, I reckon I'll drop into cousin Zeke's place, up there in the Tassie hills, and buy a few bottles of his home-made Apple Brandy (no excise, so he sells it dirt cheap :)). As a back-up Plan-B I better also get some vanilla ice-cream and generously dose it with some store-bought Chocolate Liqueur (Zeke's AB is strong stuff!). Oh, and maybe One Red Rose.

And girls also like a guy with a sense of humour (that's Axiom 2). And there's nothing WORSE than cocking-up the last line of your joke just because you can't hold your AB! So I better get a few extra bottles of Zeke's AB asap, and get a lot of practice in with it, while perfecting the smooth delivery of my lines. Yep, being able to smoothly deliver your lines is important in this comp. Practice, practice...

(Oh, yeah, and I better practice harder trying to remember her name, ummm, ... whatsit? Dammit, will have to ask Bob again... That particular detail is important (Axiom 3)!)

Anyway, I reckon while all the other suitors are comparing their chocolate cakes, and arguing about whether 20 cm square baking dishes have higher torsional rigidity than 25 cm round ones, and about ingredients, and cooking times, and temperatures, and 14 mm high-tensile bolts, Bob's sister and I (and Zeke's Apple Brandy) should be having a great time! :)

Of course, all those other clever-dick University-boys will probably complain that I CHEATED, because I didn't bake anything at all!!!

But, so what! Bob's sister is hot!!!

Z

Bartron

04-20-2014, 11:23 PM

Always gotta have enough apple brandy around.

Loz

04-21-2014, 12:38 AM

...So what can I do?...

Thinking ... thinking ... I need an advantage ...
Think harder, dammit! ... Must go back to first principles ... the fundamentals ... grrrrrrr...

...Now, how can I turn this fundamental principle into a workable plan? More thinking ...

My point above is that you need to go through this process (Thinking...more thinking...) prior to acting so that your actions return the most value. As part of this process it is important to record what you did, why you did it and whether it did or didn't work.

In terms of Bob and his sister:
If you fail to record your plan to land Bobs sister (you swore black and blue you would remember everything the next day), then during the course of the night after a few of Zeke's new batch of Apple Brandy's (these ones were stronger than the ones you practiced with), you suddenly realise that while you were looking away some other wiley character with a similar idea, spiked the punch, got in ahead of you and whisked away your prospective lady. The next day when you wake up all you have is the sour taste of bootlegged Apple-Brandy in you mouth, a bad hangover and no recollection of what went wrong because you cant remember what you set out to do in the first place.

In the case of designing a "simple little, ONE-OFF, prototype FSAE car", whether the design process solution trail is analytically iterative or proceeds as a result of the iteration of a physical prototype, the process still needs to proceed methodically from the problem definition to the action (solution). And importantly the thought process and ideas need to be recorded in some way so that you know where to iterate from for successive phases of design development. Design documentation by no means has to complete, but the ideas and logic that have led to whatever the present state is (prototype or production build), need to be complete.

This is more so true for development by way of prototype as the prototype becomes the analysis mechanism in the design iteration loop, yet it doesn't have the same "record" of development as is captured on the paper that an iterative analytical solution is developed on. If at any given point in development you cant recall what has already been done to reach that point, then the process has reverted to little more than a trial and error process, and you may find you are repeating the same process over and over, yet expecting to see different results (sounds like Einstein's definition of insanity...).

Jonny Rochester

04-21-2014, 07:33 AM

I am seeing a fair few comments here, some a bit silly, most on a tangent.

Just to make it clear, I am not the team leader of UTAS FSAE, and since team leaders are not commenting here we probably shouldn't be talking about the philosophy of the UTAS FSAE team. You are informed that UTAS plan to build a car and enter FSAEA at Calder Park. Some of you, Z, feel that we have failed already, just by deciding to do that. But we probably shouldn't be talking like that.

If I continue to use this space, it will be about stuff I am doing myself for the team (the welding) and making some little parts. I may put up my own CAD designs, which maybe used by the team, or I may just keep them for my own use.

The discussion will be about designing a low volume formula/sports car for manufacture, (or the small parts of it). When we say low volume we mean about 50-2500 units. I want to bring the focus back to rule A1.2.3 Aesthetics and manufacturablility.

Mbirt

04-21-2014, 11:46 AM

Jonny,

Would you be able to share any details about your experience with the G450X thus far? This article, http://www.atzonline.com/Article/10062/450-cm3-High-Performance-Engine-for-a-BMW-Sports-Enduro.html, shows some really cool features. Realizing that it has been "homologated" for emissions and that it has clutch inertia coupled to the crankshaft, it may not exhibit some of the "high-strung" characteristics that discourage some teams from choosing 450-class singles. Also notable are huge titanium 40/33 mm in/ex valves and the relatively vertical intake tract. The article also shows what an appropriate inlet tract length looks like for the stock 7500 rpm torque peak.

Jonny Rochester

04-21-2014, 09:31 PM

Thanks for the article, it's of some help. We currently have the engine running on the bench with standard ECU, throttle body and intake.

mech5496

04-22-2014, 04:43 AM

Looks different indeed...might package well if running "reversed", i.e. the front to back, with some sort of geared final drive (to reverse rotation) on the side of the engine.

04-22-2014, 08:14 PM

Some of you, Z, feel that we have failed already...

Jonny,

No. YOU told us that YOU AIM TO FAIL.

Posted by Jonny, back on page 9:
It is unrealistic to expect to win in our first year.

Next year will be the same, "Oh, we're only an inexperienced second year team, so we can't expect to win...".

In ten years time it will be, "Oh, but, we're only a small team from this tiny little island, and we've never done well yet, so we can't win..."
~o0o~

Meanwhile, Bob's sister is sitting in the corner like a wall-flower, surrounded by chocolate cakes she DOES NOT LIKE. She waits, reluctantly, until the end of the night when that young Monash boy takes her home, because he's the only one who ever bothers talking to her.

Well, maybe next year young Auckland will win her heart, because he at least does try to catch her eye. But so far he always manages, half-way through the night, to fall flat on his face! (Ahhh, over-exuberant young love... :))

But what a missed opportunity for the other 20 odd young suitors at Bob's annual FSAE soiree. All of them in the kitchen, comparing cake recipes, and deciding how many extra layers of icing they should add next year...
~o0o~

In case the above is too cryptic, Bob's sister;

Is NOT impressed by how fancy your push/pull-rods&rockers are. Nor with most of the other junk on your car.

She DOES LIKE a simple, compact, low CG, low Yaw-inertia body. And good "aero".

(She was an Olympic gymnast, you know...)

Z

(PS: And in case still too cryptic, "Scoring with Bob's sister" = "Scoring high points at FSAE comp".)

Canuck Racing

04-23-2014, 07:35 AM

Man went to the Moon in rocketships designed with NO CAD at all.

Nowadays, large teams of student engineers spend a whole year designing a tiny little car in CAD, then at the end of the year half of said cars CANNOT drive 30 kilometres.

By and large, the CAD, CAE, FEA, CFD, etc., experiments have proved to be an utter failure.

(Example: Compare pre-CAD Lockheed SR-71 and MiG-25, with post-CAD F35-JSF.)

Z

Careful Z, you're starting to flirt with the opposite side of the line that is currently plaguing the officials and judges - is the point to win the competition (no CAD) or become a better engineer (all the CAD)?

Jonny Rochester

07-06-2014, 09:14 AM

http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/011.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/011.jpg.html)

So a fair bit has happened. We have built a new chassis with higher roll hoop and different front roll hoop. But still some fairly large details need to be sorted.

I want to talk about the impact atenuator. None of us have done too much about it, we want to use the standard design without any testing. I have a few questions about where to buy the right sort of foam, and how it attaches to the anti-intrusion plate. And if the 1.5mm plate is welded to the chassis (stitch welded or fully welded?) will the M8 bolts still be needed? Obviously I could have researched all this better myself, but I can't do everything. Feel free to flame away...

We will have a carbon nose cone that attaches at the bulkhead somehow.

Charles Kaneb

07-06-2014, 09:41 AM

Jonny,

Coastal Automotive in Rochester Hills, Michigan sells the Dow Impaxx foam for the standardized impact attenuator. Use the US dialing code for your region / telecom service provider then it's 248-841-4001.

If you haven't started building the carbon nose cone, DON'T. You'll have as many man-hours in the nosecone as the frame. It's a similar fabrication effort to building a composite front-end tub over a mold. Sew one out of heavy polyester cloth; include either a zipper or some eyes for shoelaces to hold it on. Cover as much of your frame as you think you won't need access to with fixed Dacron aircraft cloth.

stever95

07-07-2014, 10:17 AM

Looks like your AIP is coated.

Be sure to polish all that off before welding!

stever95

07-07-2014, 10:19 AM

Also, on the CF nosecone - I disagree with Charles on this one. This year we did a good lookin', and functional, CF nosecone in a couple days with limited resources. Foam, wet layup. A little bit of wet sanding and then some clearcoat.

IMO

Jonny Rochester

07-08-2014, 04:31 AM

Our anti-intrusion plate could be the steel pictured (nasty zinc will just burn off during welding), or we could use 4mm aluminium. Still undecided what the attenuator is because the Dow Impaxxx foam is only available in USA, and being in Australia we are not sure we are going to order it. Considering all the options, aluminium perferated plate, soda cans etc... tested in house.

Or our carbon nose cone could itself be the attenuator.

So now... thinking about how to test impact attenuator.

Mumpitz

07-08-2014, 07:52 AM

That nasty zinc burning off during welding will give your welder and others around zinc poisoning. A very unpleasant experience to say the least. Wire wheel does an OK job of removing the coating but is a lot of work. Muratic acid does a great job of stripping zinc fast but is probably as big of a health concern. Outside with a good breeze away from the shop is a good idea. Or just get some un-coated steel and save yourself all the trouble, you can never have too much steel sheet around for tabs and shivs etc.

stever95

07-08-2014, 05:38 PM

Jonny, I think there may be some confusion here.

If you do a welded steel AIP, you can bolt the standard IA directly to the steel via 4 x 5/16 g8 bolts (or metric equivalent)

I cannot speak for why it's better to use aluminum... I doubt that is the case though. Adds more bolts and tabs and equivalency issues.

I highly encourage you to use the standard IA. It's light, relatively cheap, and easy!

Jay Lawrence

07-08-2014, 11:40 PM

Jonny Rochester

07-09-2014, 08:36 AM

Yes, I am the welder. Chassis is sort of finished, and I feel tired. (Also built a chassis in Jan/Feb, we cut it up.) Plus I have done welded wishbones.

With my interpretation of the rules, the anti-intrusion plate (1.5mm steel or 4mm aluminium) can be either welded or bolted to the front bulkhead. If it is bolted, we use 4x 5/16" or 8mm bolts. T3.21.3 But the rules do not say how the (foam?) impact attenuator is attached to the anti-intrusion plate. It only says it is to be "integrated", so we can use any bolts we want, or glue, or welding.
T3.21.5

Our UTAS car in 2002 had a aluminium folded plate attenuator, but there where next to no rules about this at the time, and it would not currently comply.

tromoly

07-09-2014, 12:34 PM

Glue, Aluminum straps around the IA that are bolted to the bulhead, Welding, all have been done by our school in the last few years and all have passed tech with no issues.

Alumni

07-12-2014, 05:58 PM

Mumpitz, Jonny is the welder...

For comparison, Wollongong has always (AFAIK) used an aluminium backing.
Out of interest, has anyone ever had need of their IA? Wollongong has broken one (in an embarrassing (driver related) occurrence at FSAE-A 2004 on the practice track...), but I don't think I've seen others.

Kumho University did in 2013. Pictures are about half way down the first page courtesy of Mr. Floresca.

https://www.flickr.com/photos/95685677@N07/sets/72157633470333703/

Of particular note is that they appear to be using the spec attenuator but the frame/bulkhead has clearly failed while the attenuator shows nearly no signs of energy dissipation. I was quite surprised when there was no rule changes last year as a result of this incident (though the course did change to eliminate the slow, technical right-hander that hung them out in that section.)

Ben Craig

07-15-2014, 10:46 PM

Alumni

07-16-2014, 06:27 PM

I'd like to echo others in applauding Jonny in continuing to post progress and hold relatively open discussion about this car.

For what its worth, I was at F2013 Michigan and got a pretty close look at the Kumoh car after the incident. From a few feet away it looked very apparent that their AIP was only stich welded @ roughly 1 inch weld length per 4 inch span, but don't take my word for absolute truth.

Isn't that what everyone does? At least those not using bolts or with a tub? I don't think I've ever seen anyone seem weld their AIP, nor would I have ever considered it as a student or tech inspector.

tromoly

07-16-2014, 09:18 PM

Looking at pictures of our 2013 car our AIP had ~3 stitch welds on every side (corner, middle, corner) with each stitch about 2-inches long, the sacrificial piece used for IA impact testing held with no problems.

Jonny Rochester

07-17-2014, 08:12 AM

I know this forum has slowed over the last 8 years due to greater use of facebook and other forms of sharing, and private facebook groups etc. At my risk and for your entertainment let me share a few non-academic pictures. This is reality, it's hectic, things can get messy. UTAS will present themselves professionally when that time comes, but I may use this space to show some problems (if you can spot them but keep it light hearted) with no intention to degrade other UTAS students.

This is our CNC milling machine. It is operated by one of three staff members, not students. We also have a CNC lathe that gets less used.
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/002.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/002.jpg.html)

Driveline bits are already done:
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/025-small.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/025-small.jpg.html)

The uprights are started, and now are the main thing hogging the CNC mill, and could make or delay our "car on wheels" day. This is a front upright which is not finished. How often do you see pics of unfinished parts? I am told the program code is called MasterCam, and it's not 100% fool proof. We had a mistake where half way through the tool forgot where it was and cut back into the job. We think this upright can be saved, but this just gives an example of problems the workshop can have.
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/003-1.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/003-1.jpg.html)

Jonny Rochester

09-04-2014, 09:04 AM

Embarrassment! I will leak a nude photo just to flirt.
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/015.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/015.jpg.html)
I am having massive misalignment due to binding forces and flex in the steering. I will make a brace, but I am trying to find if I have something fundamentaly wrong with the cardan joint. The 2 angles are made equal.
http://i220.photobucket.com/albums/dd310/JonnyRochester/UTAS14/013-1.jpg (http://s220.photobucket.com/user/JonnyRochester/media/UTAS14/013-1.jpg.html)

09-04-2014, 09:23 AM

I am having massive misalignment due to binding forces and flex in the steering...
... I am trying to find if I have something fundamentaly wrong with the cardan joint.

Jonny,

Yep, you sure have!

Rule 1 of Cardan Shafts: Each (1 x UJ) requires (1 x bearing support) next to it.

Easiest would be to put a bearing (could be a plastic bush) near the top of the almost vertical shaft.

Z

(Edit: PS1. On further inspection, said bearing could be mounted onto a bracket that runs underneath the horizontal steering-wheel-shaft and extends forward. This bracket could be bolted onto (or be one-piece with) the two bearings carrying the steering-wheel-shaft.

PS2. Strictly speaking, you should also have some sort of flex-joint at the entry to the R&P. This could be a UJ, or just the fibre-disc type used on production cars.)

Jonny Rochester

09-04-2014, 09:29 AM

Yep, I will make a bearing / support. The support brace maybe a vertical bar from the rack all the way to the top, holding the bush just below the uni joint.

But some trucks have cardan joints for driveshafts [edit] where not every uni is supported, and also for steering. I am having trouble getting my head around which joints need supporting when designing this.

09-04-2014, 09:46 AM

Jonny,

I added a bit to my previous post.

In the olden-steam-engine-days whole factories were powered by a single steam-engine out-back, which then drove multiple overhead driveshafts running the length of the factory. The Rule was as in previous post: 1 support bearing per flexible joint.

Z

mech5496

09-04-2014, 09:49 AM

Z, the pinion on the steering rack could serve as a "bearing" or rather bushing for the one joint, so you just need another one on the upper, almost-horizontal part. We have been running like this for years with no issues.

Jonny Rochester

09-04-2014, 02:43 PM

http://jagsthatrun.com/Pages/images/Double-cardan-0246.jpg
http://www.4xshaft.com/images/cv_angle.gif
Here we have a unsupported uni joint, so I'm still wondering what the principle should be.

mech5496

09-04-2014, 03:01 PM

Actually you do not...the top is supported by a gearbox bearing, the lower by the axle pinion bearing.

09-04-2014, 09:19 PM

http://jagsthatrun.com/Pages/images/Double-cardan-0246.jpg
http://www.4xshaft.com/images/cv_angle.gif

Jonny,

The photo shows a Double-UJ type joint that is (or was) quite common on the outer-CV of front-wheel-drive cars. It needs the two UJs to approximate "CV", and also to get enough angularity to cope with large steering angles. Its use on the "prop-shaft" is to cope with large angles for off-road driving (my guess from the link)

I cannot be sure, but I would bet that if you take that Double-UJ apart you will find that inside the short-central-shaft is a sliding-ball-and-socket joint that connects the two outer (ie. L&R) shafts. This ensures that the two UJs are always at equal (or almost equal!) angles. In effect, the Left shaft in the sketch (Right one in photo above) is well supported by the gearbox bearings, and its end then supports the beginning of the Right (propeller) shaft via the sliding-ball-and-socket.
~o0o~

I wrote my previous posts after midnight, so NOT quite right. Those old factories often had their driveshafts connected by "drag-links" which are a type of 5 DoF joint. Those required each section of shaft to be supported at both ends (so two bearing-supports for each shaft). The drag-link then adjusted for all movements in the supporting structure, other than the rotation.

However, shafts that are connected by the standard "Hookes-Joint" type of UJ need only one bearing-support per UJ. However, they also need a splined section if any axial movement must be accomodated. "Tripod" type joints are like a UJ + spline.
~o0o~

Another option for your car.

I guess the almost-vertical-shaft is splined to the input of the pinion-shaft of your R&P? The problems you are having is that because the almost-vertical-shaft has such a long cantilever it is bending sideways, hence the short-UJ-shaft is binding.

One solution would be to modify your R&P so that it has a long "snout", that is bolted solidly to the Rack housing, and that rises up and encloses the almost-vertical-shaft. The almost-vertical-shaft, which is now effectively a rigid extension of the pinion-shaft, can be supported by a bearing at the top-end of the snout, as close as possible to the UJ. The top of the snout (which is now part of the R&P housing) can also be fixed to chassis somewhere up high.

The above paragraph probably describes the topology of Harry's layout, although I am guessing that Harry's car has a much longer central section of shaft (ie. replacing your short-UJ-shaft).
~o0o~

Geez, this would be a lot easier with a simple sketching facility... :)

Z

(PS. I really enjoy watching your build Jonny. Please keep posting! :))

Jay Lawrence

09-04-2014, 10:41 PM

Design upgrade idea for next year: use a bevel box

09-05-2014, 07:21 AM

For those interested in Double-Universal-Jointed-Shafts (DUJS, aka Double-Cardan..., and lots of other names).

1. Photo of normal DUJS.
http://www.octis.it/static/images/octis-products/double-cardan-joint.png

2. Good advice for normal DUJS.
http://www.hansbuehler.com/wp/wp-content/uploads/einbau_wellengelenk_eng_41.gif

3. Photo of DUJS, BUT (!!!) WITH a CENTRING BALL (this type is typical on outer-CV of front-wheel-drives, or similar application).
http://www.billjohn.com/articles/drivetrain/tomwood/images/dshaft00e.jpg

4. Cross-section drawing of DUJS WITH a centring ball (there are many detailed variations of this).
http://patentimages.storage.googleapis.com/pages/US2067286-0.png

Z

Jonny Rochester

09-05-2014, 07:25 AM

I did not know about that ball and socket inside the joint before, or had forgotten. As a mechanic I have probably greased many, if it has a grease nipple. Our joint obviously does not have that ball and socket connection. After seeing how much force will be needed to keep this in line, I think I will have a full length brace from the rack bolts right to the top of the chassis. It will be a 5/8" 4130 tube running just in front of that almost-vertical 5/8" column with a bearing (nylon bush in steel ring) just under the uni joint.

The bevel box option we looked at in the beginning of the year would have required us to make our own bevel box which may have been beyond us at the time.

slicktop

09-05-2014, 08:46 PM

Jonny,
Have you tried removing the vertical shaft and then giving the steering wheel a spin with just the horizontal shaft and double cardan in place. That should give you an indication if the two upper bearings are misaligned. Also how is the vertical shaft attached to the pinion shaft? I assume that the pinion has a male spline, correct? So did you weld a female spline to the vertical shaft? If so, the female spline and vertical shaft may be misaligned due to welding. Take that vertical shaft and throw it in the lathe and give it a spin, you will be able to see clearly if there is any misalignment. Getting the steering system to operate nice n smooth is not easy, have had many troubles with it also in the past. Best of luck.

Jonny Rochester

09-06-2014, 01:27 AM

The rack has a male spline. The female spline is welded to the tube. It is fairly straight, I'm not worried about that. We tried to line this all up while welding it into the chassis. With a shim or 2 it is now straighter than it was, but I'm not worried about that. Unloaded, the steering works fine, light with no binding.

On the ground, there is significant steering load (as expected due to no power steering, a fast rack, small steering wheel, smallish 70mm toe-base, and maybe 6.5 deg caster). At one orientation on the uni joints, this works fine. But when the uni joints are turned 90 degrees around, just a small load is enough to push the lower steering column (between rack and uni) off to one side causing bind. The column will be pushed either left or right depending which way you are steering. This is causing the rack mounts to flex a little (I'm not worried) and causes this lower column to flex a lot. But I now know the real problem, we just need a supported bearing under the uni joint and I won't be so worried about flex or misalignment elsewhere.

Mitchell

09-08-2014, 12:22 AM

Have you considered throwing those evil contraptions in the bin and running a straight shaft? Zero play, lighter, simpler and your forearms will thank you.

Jonny Rochester

09-08-2014, 05:02 AM

One reason our top steering column is near horizontal is because the steering guy wanted fore and aft adjustment. We now have heaps of adjustment, but considering you can't adjust this during competition (as we read the rules) it would have been better to give our attention to the seat(s).

Jonny Rochester

09-08-2014, 09:32 AM

Next topic/question: Our harness has snap locks, so I want to use 7/16" eye bolts, or maybe just a solid bar bent over and welded in equivalent to a eye bolt. Is there a way we are allowed to screw eye bolts into the harness bar? I could have a threaded cylinder welded into the harness bar, but just not sure if we are allowed.

Jonny Rochester

09-08-2014, 07:37 PM

327

I would like to attach the eye bolt to the harness bar like this, (or 90 degrees from that with the eye bolt facing forwards) obviously a threaded cylinder welded into the harness bar. There are a few other places around the chassis I would like to put a similar thread. But reading the rules in the most strict way, I'm not 100% sure I'm allowed because it involves drilling a regulation tube. Any comments?

tromoly

09-08-2014, 08:05 PM

Can you remove the snap locks? Personally I would rather wrap the seatbelt around a tube than deal with making a mount for shoulder belts.

i6overboard

09-09-2014, 09:45 AM

Eye bolts are strictly prohibited in Baja for seat belt attachments, I assume that would be the same for FSAE. They want the belts in double shear tabs or wrapped around the tube.

Jonny Rochester

11-10-2014, 05:55 AM

Here is another funny one for you. Our discs happen to be anodized aluminium from the Wilwood catalog. They have 3 bolt holes each, with a chamfer for a 1/2" flathead bolt, or in our case we have used 12mm grade 8.8 bolts.

409410411Regardless of being a large bolt and appropriate, I know the rules are generally against flathead / countersunk bolts. I got our team leader to email the authorities on this... and we are told we can not use flathead / countersunk bolts for the braking system. (Perhaps we should have more clearly stated our case, and included dimentions etc... but too late now). So I have invented this silly collar so we can mount the disc with smaller 8mm bolts, but legal because they are capheads, not countersunk!

Jonny Rochester

11-10-2014, 06:00 AM

As you can see the collar had to have it's own counterbore so the head of the bolt could clear the upright. Our workshop technician is in disbelief that we are forced to make a smaller bolt! So maybe you can validate for me that I do indeed need to do this.

Pat Clarke

11-10-2014, 06:29 AM

Jonny,
There has been a blanket ban on the use of countersunk allen screws in 'safety critical locations' for several years. I would imagine brake rotor retention would be considered 'Safety critical', hence the response you got from the rules committee.
Why are they banned? Simply because there have been failures where the head has come off!

I agree your solution seems to be ludicrous and I would check the rules committee about it.

Bottom line.
The rule barring the use of such fasteners has been in the rulebook for several years. You should have known this before ordering brake rotors that required that kind of fastener.

Pat

Jonny Rochester

11-10-2014, 07:07 AM

We didn't order these brakes. We already had them from the 2001/2002 FSAE car. But you can still buy this stuff from Wilwood. I also made the team aware of this early in the year... but internal issues etc...

Jay Lawrence

11-10-2014, 08:37 PM

Jonny,

Not sure how much flex you're expecting but I wouldn't be surprised if that solution results in some upright 'tolerancing' on track. Honestly brake rotors are dirt cheap to get made so at this point I'd probably bite the bullet and get some profile cut. You can probably make them thinner from steel, thereby increasing your clearance and allowing SHCS use

12-19-2014, 10:34 PM

And now that the fat lady has sung .....

BIG CONGRATULATIONS to UTAS for 14th Overall (out of 22) at FSAE-Oz-14!!!

Especially big congratulations to Jonny for his pre-Sunday all-nighter that allowed the car to finish both Enduros. Just think, if the car could have performed on Saturday, in Acceleration, Skid-Pad, and AutoX, as it did on the Sunday, then an almost certain 10th place would have been achieved!
~o0o~

But now it all starts again... :)

Soooo ... what changes to make for 2015?

Add stuff, like a plenum?

Subtract stuff, like mass (or P/PR&Rs!)?

But don't forget the new Rules!

For example, "2015 Noise Test" will be much harder to pass... So, a big muffler? Or maybe forget about that new plenum! Seriously, I reckon a well-designed car could be Top 5 with only the 30 crank-hp that is possible from a single without plenum.
~o0o~

Bottom line, IMO a good place for all UTAS-15 students to start their Design Review is by re-reading this thread. Lots of useful stuff here...

Z

Jonny Rochester

12-19-2014, 11:20 PM

Jonny Rochester

12-19-2014, 11:22 PM

This shows me putting the engine back in at 2am in the Monash workshop on Sunday morning.
457

I show this pic because you can see the rear suspension and stuff.

It's "brown go-kart". Our members looked confused when judges asked where all the innovative electrical components where.

Jonny Rochester

12-19-2014, 11:51 PM

Some main problems I've identified myself:
1. Steering is way too heavy. Some team members are jumping to conclusions as to how to fix this. The first thing to try is just adjusting castor and SAI with shims, costs nothing. Castor is currently 6 or 7 deg (not measured) and SAI maybe 14 deg. We can change this to SAI 12 deg, and castor to zero if we want. Worth trying. It would take a hub redesign to get a Kin Pin angle of zero and low scrub radius. New uprights could give a larger toe base, currently at 70mm. A slightly larger steering wheel may help.
We have chatted to Mittchel from UQ about steering wheel angle and ergonomics for using arm muscles.
We will retire our 1" hex quick release steering hub, it has too much movement. We will buy a spline type next.

2. Rear track is too wide at 1300mm.

3. A single with restrictor and no plenum is bad for power. Not hard to understand this. Tokyo Denki suggest 4L as a good size for a single. But in endurance, this was not the main thing that stopped us, torque felt good. And it was much better than our orifice plate we tried weeks earlier.
458

4. Our car with driver is front heavy causing understeer. We can easily feel this understeer/oversteer when we are testing on poor tyres. With good tyres you have to drive alot harder to feel the natural understeer. I think it is good to drive a car hard on poor tyres, to test the balance. Once are car is handling and turning good on poor tyres, it will be lightning fast on good tyres. There are some obvious features that cause our cars nose to be big and heavy, so getting the weight balance right on a new car won't be hard.

mech5496

12-20-2014, 03:12 AM

Jonny, we had the same problem with you in the past regarding steering effort; our biggest problems caused by scrub, which is really hard to get right on a 10" with realistic KPI values and double wishbones, so you might wanna take a look there. Reducing KPI (SAI) will increase scrub, so you might wanna go the opposite way. I can second that hex-style quick releases are crappy, or at least the one we had so far. I can recommend SPA for some nice ones. Formula Seven ones seem well made as well, and judging by other products we have bought from them, they really are, and at a fairly reasonable price. Not sure how easy/cheap is to get them there though, as both companies are based in Europe.

DMuusers

12-20-2014, 09:25 AM

Thanks Z, just about to post here myself.

I could rant about what happened and give the full story of events, it was epic, but I'll try to stick to design details here.

We came 14th overall, and we came 11th in design. 220kg.
We also won the CAMS award, and came 3rd in fuel efficiency.
We also attended the driver swap day at a go-kart track on Monday, which I see as another success! Members of Monash, Tokyo Denki, Melbourne and RMIT got to drive our car and offer feedback. (By this stage we had newish tyres, but steering was too heavy, and I gather power was lower than other cars. )

I'll try and show what our car looked like, and people can comment on design.

The tie rod seems awfully close to the lower balljoint on the rear uprights. It will probably cause a lot of compliance during driving causing the rear tires to effectively steer.
What is the CoG height, longitudinal and lateral position with driver and at what ride height? Also, what is the sprung and unsprung mass with driver?

Jonny Rochester

12-20-2014, 07:53 PM

People have commented about the rear uprights. The toe-base is 75mm and the upright sits inside 13" rims. Interestingly the front toe-base is 70mm but no one comments on that. I have pointed out to the judges and others that I wanted the tie-rod to be near perpendicular to the rear upright. If it was on an angle, that could be of more concern than a narrow toe-base for compliance. We didn't have a problem with it, but if there is come compliance it rates lower than about 10 other real problems we have.

People also comment that the rear rocker pivot is not on a node, and the rear shock mount is on a node. That is the theory. In practice our design works very well and causes no problems at all. The shock points towards a node, if that is worth something. And the pivot is near a node. It is not in double sheer, but the post is strong. So we take a weight penalty? It would be interesting to measure actual deflections.

We have not been able to find CoG or the mass of the wheel assembly. We maybe able to do that and use those figures for next years car.

mech5496

12-21-2014, 02:51 AM

An easy to do thing (and a valuable exercise) was suggested by Z somewhere in those forums. Build yourself a compliance measuring rig, just some ratchet straps, fishing scale and dial gauges will do the trick. Then you can quantify suspension system deflection and know if the toe base is good enough or not. You can use the same method to measure wheel/hub/upright/chassis deflection and the total one and see which areas need improvement. Worth doing it IMO.

EDIT: I just saw you mentioned something about rubber mounting your engine for 2015. We had a rubber mounted single back in 2008 (it was solid mounted in 2007). We kept it like this for maybe a week, then lathed some teflon bushings for comp, and right after comp we replaced them with aluminum ones...

ChristianChalliner

12-21-2014, 05:56 AM

Jonny,

No one comments on the front toe base because (if you suffer the same problem as in the uk) then it is difficult to find a rack which is fast enough to cope with large toe bases without requiring excessive wheel input. Similarly, any toe compliance at the front can be compensated for by more wheel input, that's not the case at the rear. You're right about the arm angle, if it's perpendicular to the car centerline the loads will be lowest, remember this is a 3D problem though so don't neglect the angle it is to the ground plane when viewed from the front.

To be honest though it's quite easy to fit a 100mm long pickup in at the rear on a 13inch wheel but remember that you also want to be going for minimal scrub radius (if the tyre has no advantage in the first place it can't set up a moment about the steer axis).

Z has been saying for years though about front steer arm lengths but i think most of the problem is generated by rack speeds which are too slow to achieve this.

Also, i'd just ditch the push/pull rods and rockers, then there's no need to have the conversation about unsupported pivots because there aren't any! :p

DMuusers

12-22-2014, 09:51 AM

I didnt comment on the front steering link mainly because there aren't any pictures of it ;) . If there is the same amount of distance in the front as in the rear then I also think it will lead to a lot of compliance making the steering compliant. If the design judges say that it's bad design, you have to prove them it isn't. Show them measurements of deflections per load and show the amount of weight saved for larger moment arms. Then translate those weights to points for mass vs the amount of mm compliance. If it is little, it's a good explanation during design, if it is a lot it's still a good explanation for design judging where you can say you learnt something and would do it different next time round.

Don't be afraid admitting cock ups during design, be afraid of not admitting them.

JSR

12-25-2014, 03:01 PM

Some main problems I've identified myself:
1. Steering is way too heavy. Some team members are jumping to conclusions as to how to fix this. The first thing to try is just adjusting castor and SAI with shims, costs nothing. Castor is currently 6 or 7 deg (not measured) and SAI maybe 14 deg. We can change this to SAI 12 deg, and castor to zero if we want. Worth trying. It would take a hub redesign to get a Kin Pin angle of zero and low scrub radius. New uprights could give a larger toe base, currently at 70mm. A slightly larger steering wheel may help.
We have chatted to Mittchel from UQ about steering wheel angle and ergonomics for using arm muscles.
We will retire our 1" hex quick release steering hub, it has too much movement. We will buy a spline type next.

For the quick release i would also consider the "momo" style connection, as we had problems with play after ~500 km of testing with a spa spline type connector.

http://www.saferacer.com/momo-steering-wheel-quick-release

One of the things we wanted to improve for this year was also the heaviness of the steering, and we got down to scrub ~25mm and trail ~28mm with 10" wheels. Toe base was around the 60mm mark, and was really light and nice. Trail could have been even lower if we wanted to, but we choose not to so a-arms could be spread more apart for better loadpaths into the monocoque.

CWA

01-05-2015, 11:31 AM

For your steering effort problem:

First figure out how much of your excessive steering effort is due to:

A. Lateral force+trails+steer ratio
B. Wheel load lever arm (your steering geometry)+spring stiffness+vehicle weight

To further shed light on the situation:

1. Consider how much steering angle you were using at comp, and consider whether you could afford to use some more?
2. With the car in the workshop, place some paper between your front wheels and the ground to negate contact-patch-rubber twisting torques. Steer the car and see if you can compare from memory/with torque measurement data how heavy the steering feels in this test compared to when the car is out on track.

One of our cars was built with some crazy steering geometry and the drivers suffered with high effort during initial tests. Without jumping the gun and blaming our steering geometry, we realised that although a fair component of the steer torque was due to weight jacking, we had enough scope for adjustment with steer ratio, as we were only using about 90 degrees of hand-wheel angle in the tight turns.

So maybe a simple steer ratio change could be enough to solve your issue, and purchasing a rack with a different c-factor (and selling your old one) might be a better use of team resources than designing and manufacturing brand new uprights (money vs time & money). This is what we found in our case at least.

In my experience, typically mechanism A is always a much greater contributor to steering torque than mechanism B. Even in FSAE with large steer angles and funky steering geometries packed inside small, wide wheels.

Tim.Wright

01-05-2015, 01:24 PM

What are the trails on the ground Johnny? I mean caster and scrub, in mm. The angles are largely irrelevant when talking about steering torque.

My old uni had heavy steering for a few years and its a killer. In the end reducing the scrub radius helped a lot if I remember correctly. Could never figure out why that was to be honest.

Whats your overall ratio too? Steering_Wheel divided by Toe_angle I mean by that. If its too fast, this will also cause a high steering torque. Changing the rack or the toe base is the way to fix that.

MCoach

01-05-2015, 10:56 PM

Tim,

scrub radius has a similar effect to caster trail. You can think of it as scrub trail. It's a length that a moment is generated about. The longer it is, the heavier your steering will be at a stand still, and a little less heavy when actually driving, but still heavy. I don't remember off the top of my head how it works out but I believe it's: Fy * caster trail; Fx(?) * scrub radius are your loads. From there, upright steer arm length will cut the force down required by the driver, and then into the rack to gear it down further, then to the steering wheel to cut the force down again to whatever he/she may need to input.

Most people only take caster trail into account (or mistakenly caster) rather than caster trail and scrub radius. You could theoretically have a huge caster angle and equally high KPI, but still have a wheel you could flick around with one finger.

If you forget about scrub radius, it could really ruin your day when you run out of breath after 5 laps or so.

CWA

01-06-2015, 06:43 AM

I don't think what you've described is quite accurate, MCoach.

Whilst scrub radius and castor trail are similar in that they both describe steering axis-CP centre ground level offsets, each value contributes to steering torque in rather different ways. If you consider scrub radius being a lever arm for longitudinal forces which generate steering torque, this mechanism's contribution to net hand-wheel torque is going to be much lower than trail/FY-generated hand-wheel torques. This is because usually (ideally?) any longitudinal forces you see at the front wheels generate opposing steer torques, and so net torque at the hand wheel is comparatively small*. This includes both braking force and rolling resistance. Whereas trail/FY-generated steering torques at each wheel are summed together to generate a comparably large hand-wheel torque.

*(perhaps asymmetric bumps change the situation, but this is not what we are talking about).

Scrub radius can make its most noticeable contribution to steering torque when coupled with some castor angle (and/or KPI), in the form of a 'jacking' mechanism seen most commonly in karts. The steer torque generated via this mechanism is HWA-dependent, and is also proportional to the stiffness of axle springs and vehicle weight.

In my (predominantly FSAE) experience; scrub radius, even when coupled with 'large' amounts (by FSAE standards) of all the variables it depends on to contribute to steer torque (CA, KPI, spring stiffness, weight) is not as influential as trail is. If you doubled this given FSAE car's scrub radius, the steer torque increase would not be nearly as great as if you doubled the trail. And if you ever have zero CA and zero KPI (a vertical kingpin, theoretically I suppose), scrub radius does not really contribute to steering torque at all.

So yes, whilst scrub radius can influence steer torque, I do not think it is nearly as important to consider as you have alluded to - and it's contribution is always heavily based on other system parameters. Whereas an increase in trail will always increase steer torque, pretty much regardless of other system parameters.

scrub radius has a similar effect to caster trail. You can think of it as scrub trail. It's a length that a moment is generated about. The longer it is, the heavier your steering will be at a stand still

Maybe I have misunderstood what you are trying to say here, but a larger scrub radius will not necessarily generate heavier steering at a standstill. Usually the opposite is true, where the torque required to twist the contact patch rubber at a stand-still with centre-point steering (zero scrub radius) will be a significant contributor to hand-wheel torque levels, in comparison with allowing the steered wheels to roll about even the most minimal of scrub radii. But in any case, I don't suppose FSAE-ers are too worried about stand-still steer torque levels; I believe this is (used to be?) a predominantly automotive consideration.

MCoach

01-06-2015, 09:35 PM

I think I was a little too vague above. Yeah, they contribute to steering effort in different ways, that's a given, just trying to point out that steering effort will be unhappy. These won't necessarily be in steady state cornering, but more so uneven mu braking or other events that cause Fx imbalance. You'll be fighting for your life to keep it in a straight line if scrub radius is too high --trust me on that one. I won't argue the fact that caster trail is dominant.

CWA, with reference to what you quoted from me, I think you're thinking about slow roll speeds. High scrub radius helps cornering at very low speeds because the tire rolls around the point. However the tire will have a drag force as it rotates around the geometric point, which can actually be seen if you take the wheel and run the car lock to lock a bunch of times at a stand still (you'll look silly doing this, but trust me, it's educational) and roll the tires 180 degrees. You'll see a nice circle scrubbed in the ground and at your contact patch. Take a measurement of that radius and let me know what correlations you can draw. :) Stand still torque values can help give you an idea of how much it's contributing at speed, however that's another one of those loose and fast references. There's no chart to correlate the two, but just saying.

The part I was talking about with the light steering, I was very loosely and lazily (been a long day or few...) referring to the 'light' steering effort of center-point steering. This was very popular up until reliable power steering was invented, at which kinematics deviated from this thought process. In fact, it was advised not to 'dry' steer (steer at a stand still) cars with the first few power steering systems as the increased pressure would detonate the system.

And if you ever have zero CA and zero KPI (a vertical kingpin, theoretically I suppose), scrub radius does not really contribute to steering torque at all.
Of course. But, how many cars on the grid are like that? I'd compare that to saying that all numbers are integers if it weren't for those silly decimals...

However, one thing we're both neglecting here is that real cornering generates more than just Fy forces. If you consider a vehicle for a moment with general, everyday 'ackermann geometry' then the inside tire will steer more than the front. One thing Bill Mitchell makes mention of in his book is that the effect can be very influential on initial turn in for tight corners as the inside tire acts as a 'drag brake', generating significant Fx forces, allowing moment balance of the car to be such a way to help rotate around that front inside tire. For a loose citation it's somewhere in Racecar Engineering by Bill Mitchell, maybe someone can back me up on this with a page number?

BillCobb

01-06-2015, 10:26 PM

There are some other ways to manage Steering Torque. And what's wrong with front steering? Better to pull or push on a chain to stay in compliance ? (That's a LOADED question). Keep thinkin' NAckermann Steering geometry while you re at it. You'll need it for side-bite. These aren't Buicks.

MCoach

01-06-2015, 10:56 PM

Nothing's wrong with front steering, I prefer it, myself. :)
But I know what you're getting at, better to put the higher loaded rod in tension, rather than compress it.

Get a load of that.

CWA

01-07-2015, 02:43 AM

..but more so uneven mu braking or other events that cause Fx imbalance. You'll be fighting for your life to keep it in a straight line if scrub radius is too high --trust me on that one..

Yes Fx imbalance will cause net steer torques through this mechanism, sure, but there must have been a fair old variation in your case for it to truly cause such problems. Anyway, I would consider this a different (braking only) steer torque issue (or maybe even a 'workload' issue). This is something I thought the OP would have clarified if it were the case. I suppose my experiences with scrub radius/uneven Fx's have never lead to a situation of this level, so it is hard for me to picture. Out of interest, in this case, how much SR did you have MCoach?

Of course. But, how many cars on the grid are like that?

I did try to make it clear that I'm aware that a vertical steering axis often won't exist practically. I mentioned a VSA to illustrate my point that SR's (main) contribution to steer torque (through weight jacking) is heavily dependent on the amount of steer axis inclination. Presumably this is not under dispute, then, but it should be made crystal, so as not to be misleading to others reading the thread. If the OP has barely any SAI, scrub radius won't be having much affect on steer torque in his case.

However the tire will have a drag force as it rotates around the geometric point, which can actually be seen if you take the wheel and run the car lock to lock a bunch of times at a stand still (you'll look silly doing this, but trust me, it's educational) and roll the tires 180 degrees. You'll see a nice circle scrubbed in the ground and at your contact patch. Take a measurement of that radius and let me know what correlations you can draw. :)

I'm not sure what you are describing here MCoach, sorry. To explain the point I was trying to make another way, if you can picture (theoretically..) a vertical steering axis, so that we ignore the contribution of weight jacking when steering at a stand-still, I am trying to say: increasing scrub radius from zero (centre-point) will see a corresponding reduction of steer torque. Steer torque will reduce perhaps until the scrub radius equals half the tyre width, where the steer torque will probably be at its lowest level, because no part of the tyre CP rubber needs to be twisted any more (all the tyre rolls). Is this what you are trying to say too? Because I got the impression that you were trying to state otherwise. Plus I'm not aware of any other considerable steer torque generating mechanisms involved in this case, such as a "tire drag force" as you have mentioned. What do you mean by this?

However, one thing we're both neglecting here is that real cornering generates more than just Fy forces. If you consider a vehicle for a moment with general, everyday 'ackermann geometry' then the inside tire will steer more than the front. One thing Bill Mitchell makes mention of in his book is that the effect can be very influential on initial turn in for tight corners as the inside tire acts as a 'drag brake', generating significant Fx forces, allowing moment balance of the car to be such a way to help rotate around that front inside tire. For a loose citation it's somewhere in Racecar Engineering by Bill Mitchell, maybe someone can back me up on this with a page number?

Yes I'd hope most people on here are now aware of how ackermann affects the forces and moments acting on the vehicle body on turn in. But is this really going to be dominant in causing the OP's steer torque levels to be larger than necessary? Probably not, at least, I can't see how. And even if it were, would you alter the ackermann from what is presumably already ideal (I assume the OP did his work here) to try and solve this problem, or would you alter one of your other, more dominant tune-ables (trail, steer ratio, or SR+SAI) ? You would do the latter, which is why we both neglected to mention it. It doesn't really seem relevant.

Perhaps we are taking this thread off topic/into more detail than is necessary. I would like to think we are all aware of the mechanisms involved, and we are just arguing over how much we feel each contributes to steer torque, based on different experiences, which can only really be settled by calculations or simulations. Assuming nobody is going to do that for the OP, I'd like to think the OP at least has a better idea as to how to solve his problem now.

And Bill, I know I often fail to reply to your posts, this is usually because your technical descriptions give me much to think about and read up on. But in this case I'm afraid I'm just stumped by how cryptic it is

BillCobb

01-07-2015, 10:52 AM

There were several retorts I made some not related to the Steering Effort subject matter.

1) Better to pull on a heavily load tie rod that to push it. Buckling strains will ruin your day and always present unwanted steering compliance unless your mass budget is open.

2) Tire pressure is your biggest knob for adjusting steering torque once you have some fixed hardware in place.

3) The Mercedes feature to lessen manual steering effort is to use a larger steering wheel. Instead of 320 - 340 mm, they have used 350 to 390 mm wheels.

4) The orientation of U-joints (Cardan type) in a non-constant velocity design setup can produce a useful variable overall steering ratio. In some brands of cars, I've seen this range from 18:1 at zero steer to 12:1 at 90 degrees. I suspect this was done deliberately. Now even though the displacement gain has this ratio, the steering moment ratio is inverted: When the steering gain is low, then the steering torque gain is high (and the vice is nice). This means you deliberately design a non-constant velocity coupling between the gear and the steering wheel shaft. A single joint at high angles can do this very well but be careful about load reactions at the support points. The off axis loads can be very large.

5) A good TIRF Round 7 (or is it to be 6) tire test would be to measure scrub torque. This is the Mz vs. steer angle function at zero belt speed run out until it saturates. Since the tires are already on the machine, a quick sweep back and forth provides information that could conceivably influence a power assisted steering decision.

6) While caster seems to be arbitrarily chosen, it can be effective to comfort a driver's feeling of the max lateral capability of the car. This done to shift the MZ peak up to the Fy peak slip zone. However, use of NEGATIVE caster can be used to lessen steering effort (tierod loads) and has often been done with purely manual steering vehicles (whether you know it or not).

7) High tierod loads are generally bad for a car because the loads on the steering mechanism lead to increased steering compliance and this compliance is generally non-linear. It often must be counteracted at the gear by beefy mounts and special bearing supports within the gear to keep a rack and pinion in close proximity. Its possible in some production cars to 'jump a rack' by applying very large steer velocities (300+ deg/sec) such that the teeth separate and re-engage at another orientation.

8) I personnally like long steer arms but acknowledge that they cause other problems (limited turn radius, packaging space, possible compliance increases due to bending and special rack design details [like high C factors and rack lengths])

Steering work should be a top level design specification. It is a balance between steering angle work and lateral g build up. Human Factors studies show there is an optimum zone for human powered vehicles of this work relationship. (Look for a Ken Norman's SAE paper on this).

I hope that directly clears up the mystery of my comments. If not, well there's always next year....

Ahmad Rezq

01-07-2015, 01:36 PM

Very useful topic for non-experienced students like me who build their car for the first time.
thanks for all the contributions you posted guys.

ChristianChalliner

01-07-2015, 04:40 PM

CWA

01-07-2015, 10:21 PM

I hope that directly clears up the mystery of my comments

It certainly did Bill, thanks very much - I appreciate the write-up

6) While caster seems to be arbitrarily chosen, it can be effective to comfort a driver's feeling of the max lateral capability of the car. This done to shift the MZ peak up to the Fy peak slip zone. However, use of NEGATIVE caster can be used to lessen steering effort (tierod loads) and has often been done with purely manual steering vehicles (whether you know it or not).

I found this particularly interesting - I've often wondered if this has ever been considered/implemented in industry

MCoach

01-07-2015, 10:40 PM

To be fair, I'm harping on it because I didn't listen to what my reading material said, not because it's the most dominant variable. I just want others to be aware, and not make the same mistake. It's ok to virtually ignore in the rear, but the front is very sensitive.

CWA, 2014 was our first modern venture into the world of 10" wheels with limited options and capabilities. We chose the 10" DWT wheels which unfortunately have a poor offset for our style of cars....but they're affordable and one piece and allowed us to advance our engineering concept, so we went for it. We traded off what knew for what we saw as benefit from everything contained in our new package but brought some stability compromised suspension that was a little more of struggle to keep between the lines than our '13 concept. Fortunately, we have a good handle on how these things work at this point.

We had a scrub radius of just about 40mm in the front and the car had some peculiar handling and feedback problems. Under threshold braking the car would enter a "death wobble", typically not seen on four wheeled vehicles. The steering wheel would slap back and forth with our drivers barely able to keep it under control. This meant we were losing out on limit braking capability until we tamed our feedback by the time the Lincoln competition came around. We were also losing out on driver confidence (this being separate from some of my previous posts about driver confidence as most of the non-comp drivers didn't drive it until after Lincoln), maybe a second or so a lap, because we never wanted to touch the brakes, it took some convincing and man handling!

Anyway, Bill is certainly correct on point 2, tire pressure being worth it's volume in gold. It became my main tool to calm that savage animal.
I absolutely love your point from number 5, as it's very simple, achievable, and relevant. It adds fresh content to the TIRF tests.

I hope our discussion has given some insight to everyone, especially Jonny, as this is your thread. :)

CWA

01-08-2015, 12:12 AM

We had a scrub radius of just about 40mm in the front and the car had some peculiar handling and feedback problems. Under threshold braking the car would enter a "death wobble", typically not seen on four wheeled vehicles. The steering wheel would slap back and forth with our drivers barely able to keep it under control. This meant we were losing out on limit braking capability until we tamed our feedback by the time the Lincoln competition came around. We were also losing out on driver confidence (this being separate from some of my previous posts about driver confidence as most of the non-comp drivers didn't drive it until after Lincoln), maybe a second or so a lap, because we never wanted to touch the brakes, it took some convincing and man handling!

This is rather interesting to hear about! I've not seen any kind of wobble/shimmy issues on an FSAE car before, although I have had some experience with the issue on an eco-marathon style vehicle, which was a challenge to try and cure.

Do you have any video footage of this behaviour occurring on your car MCoach? And did you manage to cure the issue completely with SR/pressure changes? 40mm SR doesn't seem too out of the ball park to me so I'd love to hear how you guys went about tackling the issue (if it's not considered too off topic)

BillCobb

01-08-2015, 05:33 AM

Your self induced steering oscillation is probably an aligning torque camber driven phenomenon. Since caster is a steer-camber coupling mechanism, the Fx force driver can cause this high 'Q' vibration.

Just because your scrub radius is identified geometrically at some layout position, it doesn't mean that its 40mm under actual operating conditions. There is a load, pressure, camber and rim width sensitive Mx contribution to this dimension, too. I believe I posted some sample Mx/Fz function plots on the TTC Forum. If not, I can do so.
The reality is that all the TTC data is nice an tidy in a 2 axis plot but not actually relevant to a rolling tire on a flexible (and compliant) multi-bar suspension platform. You need to incorporate it into a dynamic or quasi-static model where the multi-surface tire characteristics bloom. Sure, in most all cases superposition works, but the Fz, alpha and gamma drivers need to be there. I'm pretty sure I posted such a 4D tire surface Matlab spline Simulink model of a tire test machine on the TTC site. Feed that with some open loop inputs from a simulated static braking test and comment on what you find. There could be +- 50 mm of dynamic S.R. variation and you should know by now what that means to your '40 mm scrub radius' label.

That's my positive feedback for now....

MCoach

01-08-2015, 01:15 PM

Funny that you mention steer camber effects...

There could be +- 50 mm of dynamic S.R. variation and you should know by now what that means to your '40 mm scrub radius' label.

And I would absolutely believe that. When the tire is allowed to shift the entire car because of floppy sidewalls, I am (after this year) well aware that 40m scrub radius can easily become 100mm or more while running. However this deflection can also aid in covering some goof ups like not enough or too much camber gain because the soft tires will do what they want and stand up on the track. There's some decent pictures from several competitions. Some cars on 10s have the wheel cambered several degrees and the tire is essentially straight up.

As for our fix, we reduced camber gain (longer FVVSA) by two increments, I don't think we adjusted caster, increased tire pressure by about 1.5-2.5psi, and stiffened the front springs to compensate for the roll center/camber gain reduction. The rear was rebalanced with respect to total lateral load distribution (TLLTD). This got us most of the way there and allowed us to hang on to the thing. The icing on the cake was some ackermann shim and it went completely away. We had a chassis tube added which left us with goofy steer arm geometry which may have had something to do with the last bit there...

We may have video around of the phenomena. I'll check this weekend.
I know that Auckland runs the same wheels, so I'm curious if they have run into this issue as well. I'd love to hear their input. Maybe they were too smart to fall into this pitfall. :P

Thanks for the input Bill.