Beam Axles - Front, Rear or both.

Quote:

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Originally posted by AxelRipper:
American Racing and Hoosier both make tires in 8" size for MiniCup cars.

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It's American Racer: http://www.americanraceronline...Track/mini-cups.html They claim to have "softer" compounds.

Hoosier seems to only make that one very hard 8" MiniCup tire. http://www.hoosiertire.com/pdfs/speccat.pdf (page 5) Do we have any FSAE alums working at Hoosier that could convince them to do a run of R25B compound MiniCup tires?

What does it take to get new tires into the Tire Test Consortium queue? http://fsae.com/groupee_common/emoticons/icon_smile.gif

I'm sure to a lot of people using 8" wheels seems nuts. Perhaps as nuts as a 450 single seemed in 2005. Just because there hasn't been a simple, commercially available solution before doesn't mean it's not a smart approach to the FSAE problem!

Quote:

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Originally posted by Z:

The bottom line is that suspension Bounce (=heave) and Pitch modes only need very short travel. This is easily done with beams by having short travel (+/- 5mm) bump rubbers fitted at the mid-beam position. With these the chassis can be run very low with no scraping, so low CG, but there can still be plenty of wheel travel in Roll and Twist modes to keep the scrutineers happy. The soft Roll mode is, of course, no problem because no camber change, and the undertray doesn't scrape because it is beam mounted.

Z

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Has anyone checked HOW the "minimum suspension travel" rule is measured? Usually the marshals push the car down with their foot (so suspension operates in bump) and visually check it. A solution such as the one described by Z above could not be acceptable then...Of course you could use scrutineering-specific rubber bumps and replace them for the race (suspension springs CAN be exchanged at any time and this is essentially a suspension "spring", but I do not know how the scrutinneers will feel about it; it is a bad way to get DQ. Anyone checked it with the rules yet? Instead of a rubber "spring" you could use a horizontally mounted spring/damper, actuated by a peg n slot driven bellcrank, thus having an adjustable (and dampened) heave/pitch spring...

Seriously, topics like this ARE the reason why I love the fsae forums. I would really like to have this convesation up personal with all of you, something like a design meeting with a drawing board somewhere in the room, but I'm afraid we would be discussing for days.... http://fsae.com/groupee_common/emoti...on_biggrin.gif

Have you talked to American Racer? If so, what information have you gotten about their MiniCup tires?

Splitting a 60 tire production run between a few teams wouldn't be that bad of a deal to put together. 15 sets is nothing! I think the current Hoosier MiniCup tires are only $60 each!!! I'm sure they've seen how much demand there is worldwide from FSAE, considering they seem to be out of 13" FSAE tires at least once a year. The only way to make something like this happen is to convince a company that it makes business ($$$) sense. The "passion project" approach will never work.

What were the other 8" asphalt racing tire manufacturers that you identified? My cursory search a few months back only found the two we've been talking about.

[sorry about the major thread hijack]

I dont think the rules specify how exactly they are measured, you may need a clarification on this, putting different springs in to pass shouldnt be necessary, what if you run mega stiff springs, you can have the required trvel, but you don't use it, it would need to be proven another way..

We ran into a design issue with our car two years ago, but didn't figure it out until about a week or two before competition. The kinematics our rear suspension made it incredibly stiff even with the softest springs we had ( its my fault, and I'll admit that ). Anyway, we definitely had the capability to move 2" kinematically, but in reality it only moved about 0.5" when you jumped hard on the rear end of the frame. Judges looked at me skeptically, but passed us through with no real issue.

Travel was always "measured" on our cars that way; a marshall jumping up and down on chassis...that's why I was wondering about the solution Z proposed.

Z, I was reading your thoughts on "damper histograms" thread, and I have a question... In a beam suspension like the one described here, why would anyone want any stiff mode? You could limit chassis roll by using stops, but again, why limiting pitch and roll? Besides geometric weight transfer caused by movement of the CoG while pitching/rolling(which isn't that much), I cannot think of anything obvious... Another thing is that by using beams, all the lateral forces are transferred to the chassis via 2 points for each axle (plus two for the dampers), so a fairly stiff bottom is all you need. The rest of the chassis could be really flimsy (besides crash structures) with no problems. Plus you can achieve a soft twist mode (while having harder pitch and roll modes) by making a chassis torsionally flexible....

It looks like a great idea.

But I'm not so sure about the aerodynamics.

So far we haven't seen any great aero-packages without wings that helped a lot.

e.g. Munich's car didn't seem faster through the undertray compared to a similar design from Stuttgart.

One thing I'm curious about is the "live" aero.

I couldn't find anything in all the aerodynamic papers online that said that live aero is so much better than a normal mounted aerodynamic.

I just read that the suspension can be softer but no other significant bonuses.

I guess it's good to have the force directly on the wheels but is that enough to change the whole layout of a car?


The design of the different wheel sizes is interessting. Maryland did it with 13inch and 10inch. Maybe this would help the concept too. The new 13inch Goodyear's should be pretty soft...


Cheers,

Jack

Jack,

Besides running softer suspension setup, which aids mechanical grip due to reduced tire load variation, and more direct aero load paths, it also has the advantage of being able to run the sides of the undertray extremely low, as its distance relative to the wheels is maintained. This in turn gives extremely good seal to the negative pressure developed by an undertray, and lots of downforce due to ground effect (remember sliding skirts or even better "double chassis" Lotus F1 cars?). On the negative side, live aero means added unsprung weight... IMO the main point here is not aero, as live undertrays are possible with double wishbone suspensions too, but purely (possible) kinematic/loadpath gains....

Thank you for your explanations.

I was just curious about this topic in the first place and thought it might be a good point to register and ask it right now http://fsae.com/groupee_common/emoticons/icon_smile.gif

I read Pat's column and saw that he sad ECU's aero wasn't that good as Monash's because it was chassis mounted not unsprung.

I can't see the huge advantage at the front wing for instance if it's mounted to the bellcranks or something like that..

Thanks again!

SoonerJack: I read in an older wings thread (called WINGS!), that sprung aero = stiffer springs = less mechanical grip at slow speeds (where downforce is less), so a slight problem. Unsprung aero would not have this issue.

If you've done some reading/research into direct aero, would you like to share on this thread? (or to my email/fb). In my quick Google searches, there wasn't much info. But I hadn't looked into SAE papers yet. The problem is that FSAE is one of the few classes of motorsport that allows direct aero, so not many people care about it.

Harry,

You ask, "In a beam suspension like the one described here, why would anyone want any stiff mode?"

For circuit racing a lowest possible CG is beneficial. So it is good to have all the heavy bits close to the ground at all times (so not bouncing upwards over crests, etc.). Formula cars have most of the heavy bits spread along the centreline of the car, so it is beneficial to have stiff heave and pitch modes that "lock" the centreline down low (with, say, +/- 5mm of highly damped soft motion to suppress bouncing on the tyres). A saloon car also needs a stiff roll mode (with damped +/- 5mm) so the sides of the car can be low, but don't scrape during cornering.

The Z-bar layout in the Damper Histogram thread allows a completely soft twist mode (which gives consistent LLTD over uneven ground), while stiffening up heave and pitch, or heave and roll, or all three, as needed.
~~~o0o~~~

You say, "you can achieve a soft twist mode (while having harder pitch and roll modes) by making a chassis torsionally flexible...."

And, indeed, this was the way it was done in the early days of motorsport. Prior to about 1930 the production chassis were deliberately softened when they went racing, by removal of crossmembers. However, this required the right sort of engine mounts, etc., to get the right LLTD (eg. 2 bellhousing mounts at mid-chassis, and only 1 engine nose mount). Also the torsional chassis spring was undamped, except for "inertial damping" from loosely mounted fuel tank, driver, etc. A stiff chassis with damped twist-soft suspension works better.
~~~~~~~~~~~~~~o0o~~~~~~~~~~~~~~~

SoonerJack,

You say, "I couldn't find anything in all the aerodynamic papers online that said that live aero is so much better than a normal mounted aerodynamic. ... I just read that the suspension can be softer but no other significant bonuses."

Three main points here:

1. Live aero is usually banned as soon as anyone uses it (it is too good), so you are not going to find many papers about it.

2. Sprung aero requires stiff springs to minimize ride height changes at different speeds ('cos different DF). Given the "always low CG" argument above this isn't such a big problem because stiff "third springs", which control heave and pitch, can do both jobs. In fact, most such cars have a somewhat "active aero" in that the rear "third spring" is softer than the front, so the car's rake changes from tail-up at low speed (for more DF), to horizontal at high speed.

Nevertheless, these third springs are rarely properly damped, so the car "porpoises". So, in F1, Renault fitted front and rear inertial dampers of a similar type to those used on "the world's cheapest car" (Citroen 2CV), which cheaply fixed the problem. So the moron Max Mosely banned them, initially on grounds of "cost and safety" (!!!), and later because "they are movable aerodynamic devices"!!!!! Nowadays the cars have less effective, and more expensive, "inerters". Ah, progress at the cutting edge.... http://fsae.com/groupee_common/emoti...n_rolleyes.gif

3. The beams in the sketch make for easy mounting of the aero panels. Just attach wherever and however is most convenient. If attaching to bellcranks as you suggested, then several balljoint ended pull/pushrods, plus possibly more linkages, are required in just the right places...
~~~~~~~~~~~~~~~o0o~~~~~~~~~~~~~~~~~~

More miscellaneous ramblings:
~~~o0o~~~

8" TYRES. The HyperProRacer mentioned earlier is one of the voices in the back of my head saying "13 inch is waaaay too big!". This link gives an interesting comparison of HPR with some other racecars, including an FSAE car. Maybe someone in Melbourne knows which FSAE car that was?

Anyway, the HPR is like a higher speed version of FSAE, but built to more liberal rules. It is 185kg (sturdy roll cage), Yamaha 450 single, spool-beam rear axle, good for 200+kph, and seems to do just fine on 6" go-kart tyres. Their rationale for the 6"s is to reduce running costs, which makes sense.

Even so, if I was starting today and had to be at FSAE comp in December, I would be designing for 10"s all round (wide rears, narrow fronts). Meanwhile, I'd put 8" rims on last year's car and go testing any 8" tyres I could find. Less is more! http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~o0o~~~

ENGINE. The engine in the Twin-Beam sketch was supposed to be a Royal Enfield, based on info I found on various websites. It won't work as shown. I got parts of the old and new models mixed up...

But, funnily enough, the day after I posted the sketch I was tyre-kicking in a quad bike shop and guess what's sitting in the corner? Three old British bikes - a Norton twin, Matchless 500 single, and a Royal Enfield 500! (Old Z had a Matchless 500 engine that went in every "fun" vehicle he dreamt up. I clearly remember it NOT being a great success in the canoe (I was about 10). The first time the throttle was cracked open the propellor spun maybe five times one way, and the canoe did a half turn the other!)

So I had a good look at the RE, and I like it! If lots of REs were available, at the right price, then I would certainly consider one. The long term goal would be a turbo or supercharger (with standard CR~7:1), crank driven clutch and dog-neutral, then direct chain final drive ~5:1 (ie. ditch the gearbox).
~~~o0o~~~

WHEEL PODS. Pat, if there's nothing against it in the rulebook, then IT IS LEGAL. The moment officials start interpreting the rules according to their whims and fancies, honest law abiding citizens start disappearing in the middle of the night. Well, maybe not that quickly, but that's how it starts.

Z

Quote:

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Originally posted by Z:
Harry,

You ask, "In a beam suspension like the one described here, why would anyone want any stiff mode?"

For circuit racing a lowest possible CG is beneficial. So it is good to have all the heavy bits close to the ground at all times (so not bouncing upwards over crests, etc.). Formula cars have most of the heavy bits spread along the centreline of the car, so it is beneficial to have stiff heave and pitch modes that "lock" the centreline down low (with, say, +/- 5mm of highly damped soft motion to suppress bouncing on the tyres)....

...You say, "you can achieve a soft twist mode (while having harder pitch and roll modes) by making a chassis torsionally flexible...."

And, indeed, this was the way it was done in the early days of motorsport. Prior to about 1930 the production chassis were deliberately softened when they went racing, by removal of crossmembers. However, this required the right sort of engine mounts, etc., to get the right LLTD (eg. 2 bellhousing mounts at mid-chassis, and only 1 engine nose mount). Also the torsional chassis spring was undamped, except for "inertial damping" from loosely mounted fuel tank, driver, etc. A stiff chassis with damped twist-soft suspension works better....
Z

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Thanks for the input Z! So, to my understanding you want a fairly stiff pitch/heave mode... You can achieve that with a heave/pitch spring and damper for each beam, mounted under the chassis and activated via bellcrank through the suspension vertical movement (bellcrank mounts at the peg n' slot position, so not activated during roll) and using very soft springs/dampers for all other modes. I still think a "soft" chassis as a good idea though, although "undampened", mainly because of the need of only a few mounting points as explained in my earlier post; you can just use the chassis as a part holder, cutting off significant weight. Or you can just use a longitudinal z-bar configuration!

Z: I know that both Swinburne Petrol 2010 and RMIT were at the Top Gear. I fb'd Stefan Millard, and it says he's at RMIT.

Re adding this post back in as it's not so off topic i guess:

That HPR is a mean little machine! I do have to ask why they wouldn't use a 2T in it instead of that thumper. Is it just the bad rep the little 2T's have? Surely you could find a more powerful, and lighter 2T engine, that costs half as much for a full rebuild?

Only con i see is there being less engine options for electric start in 2T compared to 4T, and of course the stigma that comes along with them.

JWard,

Your post IS on topic! (Put it back. http://fsae.com/groupee_common/emoticons/icon_smile.gif) The HPR has a beam rear axle so I think it is in keeping with Oz-Olly's original theme. It is also KISS, which was Olly's rationale for beams.

Unfortunately, I can't remember exactly how this rear beam is located, and haven't been able to find a good picture on the HPR website. FWIW, I think it has three longitudinal links (two lower, one upper central) and a panhard rod for lateral location. These connect between chassis and the oval shaped subframe (visible in some pics) that carries the spool axle. A single central monoshock S-D is used together with a fairly stiff ARB (to unload the inner wheel and thus reduce spool-induced U-S). If anyone knows better, please advise. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Regarding the four-stroke engine, I guess yes, it is there because of its "greenlyness" (and its sequential 'box).

Z

Z,

I like the design concept you proposed. Very interesting direction. I have some comments on your setup and further expansion of my double beam idea but want to ask a couple questions to pick your brain before I continue with those.

It seems that aero balance was the reasoning behind splitting the aero into front and rear underwings. I know that this was an issue with Herbs Adams wing car that they didn't have time/money to develop to its potential.

http://www.oldracingcars.com/I...America1983-1000.jpg

http://i114.photobucket.com/al...t-1983-06-05-bg4.jpg

http://www.racingsportscars.co...0.jpg?dir=photo/1983

http://www.racingsportscars.co...aunton&wi=&mode=Null

Also minimizing individual movements of the suspension modes (i.e. interconnected suspension) to keep the aero consistent in general but especially if it was a single aero element connected to both beams as to keep from wraping/breaking said aero element in whatever form is most efficient.

From the lengthy descriptions of you "z-bar" concept topic it would seem to be a great answer to minimizing the suspension mode movements enough to allow a single piece aero element to survive. Could you discuss the application of an interconnected suspension in terms of benefiting a pure aero performance driven design.

Also in from that Z-bar concept discussion:

http://i16.photobucket.com/alb...ll/ZBARFSAEsmall.jpg

In my concept I wanted to use a front and rear mumford link. I can arrange the mumfrod rockers in such a way to connect a pair of torsion z bars front to rear by running the bars right under the drivers ass. This would make for a hybrid of the two diagrams that you drew up. My question to that is would the beam axles then act as an theoretically infinitely stiff "end-pair" leaf springs. Please discuss what and how that would would work if it did.

You claim that the dampening requirements for a "z-bar" suspension would only need to be in the slow speed range. F500 cars are mandated by rules to not run hydraulic dampers of any sorts. They are forced to run polymer pucks of dimensions set by the rules. Per my comparison of the brutally low tech F500 being at every disadvantage to a modern RIT FSAE car in the engine/cvt topic except transmission as I so espoused, and how razor thin close in actual track performance it was to RIT, it seems that non hydraulic damper has some merit. If an interconnected double beam could utilize polymer dampers it would easily cut 5000 dollars off the the cost report of a car to further push this concept path. Please comment on this.

http://novakar.com/

http://novakar.com/images/features_4.jpg

http://novakar.com/images/features_6.jpg

http://novakar.com/images/features_7.jpg

http://www.formula500.org/view...8b5583e47861cfdc2427

http://sports.racer.net/chassi...vakar/elastomers.htm

Also with my love affair of F500 cars I should note that in the SCCA rule book for their class they have rules that discuss how far up the front fairing pods are allowed to come to the top of the tire as to keep the car an open wheel car and not a closed body car. Since much of the FSAE rulebook looks to be copied straight from the SCCA rulebook I think the judges may end up using the same F500 rule in the future to avoid conflicts that UWA brought up.

A couple of addendums to the above post...

Z,

Could the A/B ratio in such a scheme I described be somehow used to balance front to rear aero forces conducted into the unsrpung mass through that interconnection?


The "F500 wheelpod" rule I mentioned in Rule 9.1.1.E.9.

http://cms.scca.com/documents/...updated%20August.pdf

I would like to hear the rational as to why this has to be an open wheel format and the purpose behind it. It seems that there should be freedom to decide if you want to pursue that or not. Allowing a closed body car would probably increase the finishing rate of cars just from not taking cones to fragile pieces. Teams should be allowed to justify the weight and expense of doing it versus not. CanAm in its weaker later series was Formula Atlantic tubs with aero bodies on them which the current IRL cars are practically doing now so if the intent is for post baccalaureate jobs then it would seem the current way to go it to allow such things.

http://www.electricdreams.com/...age/IMG_0535-600.jpg

Quote:

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I would like to hear the rational as to why this has to be an open wheel format and the purpose behind it.

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Fashion.

Well if it is fashion then we need to up our game to something along the lines of the Red Bull X2010 or the Camparo F1. Seems that when F1 engineers are asked if they had a clean sheet what would they do they say open wheel F1 car with fairings that make it not so open wheel.

http://en.wikipedia.org/wiki/Red_Bull_X2010

http://en.wikipedia.org/wiki/Caparo_T1

Rob Woods is back! Too many posts on one of your favorite topics and no reply in a week or so- I was just getting worried... F500's are so neat small and simple machines, that could make a hell of a "beginners car" in FSAE. (adopted to the rulebook) The only thing I doubt of is the CVT, and I doubt because I have never dealt with one, so in my mind they are just heavy, complicated, hard to work things that make your engine sound funny... http://fsae.com/groupee_common/emoti...on_biggrin.gif

I was out of town and busy after that. Check out this post and videos.

http://fsae.com/eve/forums/a/t...20489051#51220489051

A F500 has a worse weight to power ratio, no hydraulic dampers only polymer pucks for springs AND dampening, 20 inches more minimum wheelbase, not allowed to run wings or tunnels so only really a diffuser and a 800lbs minimum weight and it ran within a couple tenths of RIT FSAE most recent car. They are terribly handicapped in every respect to a modern competitive FSAE car yet run times that are very close to competing for a win. It's ALL in the CVT. Imagine a 60 inch wheelbase(instead of 80 inch), 350lbs car (instead of 800), with a weight to power ration of 7:1 (instead of 10:1), suspension designed to integrate aero (instead of mandated suspension design), with a well tuned CVT and you can see how that would make up for a couple tenths and much much more. If you could integrate a polymer puck instead of hydraulic damper with spring you can save 5000 on the cost report. Ditch the diff and halfshafts for a solid axle and save an additional 3000. You can easily win cost and sales presentation. The possibilites for a cheaper yet more effective win are there because otherwise you wont be able to out resource (talent,funding,knowledge,facilites,etc.)a team like Oregon unless you are an elite few (maybe 20 teams).

Well, if you notice, I have commented a great deal in the above posted thread....http://fsae.com/groupee_common/emoti...on_biggrin.gif I did not say CVT's are no good (in fact I like your approach a lot) but I have not dealt with them even a little, so it's "black magic" to me, so no CVT for my car (as stated in the "objectively" thread, single cylinder with 3 gear transmission). I think I'm waaaaay offtopic now though!

I noticed Harry. Threw that one out to tie back to the other topic for the uninitiated.. They aren't all that big and scary. They are less complicated that learning a fuel injection system and that is something all teams have to go through.

Quote:

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Originally posted by rjwoods77:
I would like to hear the rationale as to why this has to be an open wheel format and the purpose behind it.

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If it's anything like the rule about the restrictor location within the system, it's still there because they think it's both "challenging" and "for safety." I'm sure if you pressed the issue that you would get an earful about how allowing for a closed body would make it too easy to generate downforce and how that would somehow lead to the cars becoming too dangerous to drive. I got the same argument when I pressed the restrictor location thing. There was also a heavy dose of "tradition" thrown in when I pressed the restrictor issue (which I also thought was silly). I'm sure they would also feel the "formula" part of Formula SAE would be gone if they weren't completely open wheel cars anymore.

As long as there is a clearly defined spec, I think it's fine to do whatever they want. I hope that the rules committee will quickly address the apparent hole in the "open wheel" issue. The rules say something to that effect in the beginning, but then there's no written definition of what that actually means!

-Kirk

I know shit about fuel injection too...http://fsae.com/groupee_common/emoti...on_biggrin.gif You are right that this is part of learning though. The thing is that despite my "fear for the unknown", all current FSAE engines have gearboxes; a CVT is more extra weight. So, possible solutions:
1) Replace gears with axles, bolt CVT; straightforward but heavy
2) Machine a new crankcase with no GB and built-in CVT; hard on resources, easier for singles (ball-bearing bottom end, simpler lubrication, split stock crankcase)
3) Electric drive; far from simple, a bit heavy compared to singles, expensive, but lots of torque, direct drive, more powerful than any 4-cyl.

In fact we are going no3. this year (and this was a decision of our faculty which in first did not like). I know that this seems way off the "simple" way, but I assure you that our car is gonna be simple as hell; direct drive from the motor (no reduction), no torque vectoring so a simple powertrain, components and mainly batteries placed for minimum Iz. The thing is that I have a hard time convincing our faculty to go "low tech" (beam axles), especially now that we spend a lot of money to go "high tech" (electric)... The good thing is that I like this way so much, that I have already made tons of research on my own. Actually I will have some of our team members do some quantitative analysis on gains/losses on a "beam axle" car, but after the exam period is over, which I will post around here for reference (unless we decide to go that way after all...:P)

Funny you mention electric. I was thinking the other day how easy it would be to make a double beam car with a pancake motor in each wheel.

(Just edited above post). OR wou could make a 4WD electric car, benefiting from aggresive regenerative braking to cut down battery pack size and use a well-tuned torque vectoring system to aid vehicle dynamics... I will have my eyes open for Delft this year, they go 4WD and they cut down their battery pack about 13kg (per my calculations based on data about their new batteries), so it might get interesting!

Some comments regarding:

AERO
=====

(Rob Woods quote)
"It seems that aero balance was the reasoning behind splitting the aero into front and rear underwings."

Rob,

Yes, the Twin Beam-Wing is intended to give maximum aero performance for minimum effort, which includes minimum understanding of aero. This means easy set up of, and stable, F/R balance. Hence the two wings with their separately adjustable flaps and downforce. There will be some inevitable interactions between the two wings, but hopefully easily managed. More downforce is possible (from full undertray) but that requires better aero understanding, especially regarding F/R balance.

IMO the Herb Adams' Catamaran-Wing-Car in your links likely suffered from excessive pitch sensitivity of total DF and F/R balance. Even with rigid suspension and a perfectly flat road any slight nose-down pitching, say from tyre squash, brings the nose splitter closer to the road, which creates a thoroughly "unsteady" flow condition, which first increases front DF, but then the suction travels further back ('cos unsteady), etc., all of which is a killer for predictable handling.

Incidentally, the smooth upper-body surface possible with the catamaran layout is not necessary for good aero DF (although maybe a small advantage for low drag). A wing can only have a maximum Cp=+1 on its pressure surface, while Cp<-10 is possible on the suction surface. A similar 10:1 ratio applies over the whole surfaces. Bottom line is that the top surface of a racecar is of little importance to DF, because all the action is underneath (with some qualifications http://fsae.com/groupee_common/emoticons/icon_smile.gif). A good example is military aircraft that have a dog's breakfast of bombs, missiles, fuel tanks, etc., stored on the pressure side of the wing, but rarely anything on the suction side.
~~~o0o~~~

The best way to deal with aero balance problems is via the aero design (ie. as noted above, even rigid suspension and flat roads can't fix some problems).

Nevertheless, you ask,
"Also minimizing individual movements of the suspension modes (i.e. interconnected suspension) to keep the aero consistent in general but especially if it was a single aero element...
Could you discuss the application of an interconnected suspension in terms of benefiting a pure aero performance driven design."

Conceptually, the best way to have a single rigid aero element and keep it at a consistent height and attitude above the road surface, is as shown at top left and right of the Z-Bar sketch (redisplayed below). This is perhaps best understood in the top right sketch where the diamond shaped structure (say the aero element) is positioned relative to the uneven road surface such that its two side-points are at the average height of the two side-pairs of wheelprints, and its two end-points are at the average height of the two end-pairs (axle-pairs) of wheelprints.

Strictly speaking, these sketches are over-constrained. The diamond structure only needs three of its corners attached to the mid-points of three of the "balance-beams" (or "averaging-lines") that interconnect the four wheels. This three-point support (like a tripod) controls the diamond's heave, pitch, and roll motions. The symmetry of the four point support helps with understanding, and is better structurally (better distribution of loads).

Many different practical implementations are possible, but something close to the top left sketch, though with lightweight and rigid Side-Pair-Balance-Beams instead of centre-pivot-leafsprings, and BJs instead of coils at the beam-axle centres, would work. The SPBBs could do double duty as beam-axle locators. The chassis would then sit on four soft coil springs arranged in a diamond pattern on the centres of the 2xBeam-Axle+2xSPBB substructure.

http://i16.photobucket.com/albums/b3...RFSAEsmall.jpg

(RW quote)
"Could the A/B ratio in such a scheme I described be somehow used to balance front to rear aero forces conducted into the unsrpung mass through that interconnection?

No. The resultant of the aero pressures (ie. the aero "force screw") is always equal and opposite to the resultant of its reactions from the four wheelprints. Any contrived linkage between these "equal and opposite" forces cannot change the F/R aero balance. However, the linkage can change the distribution of the front DF acting on the two front wheels, and hence necessarily also alter the distribution of DF acting on the two rear wheels.

This is similar to a given cornering force always giving the same total Lateral Load Transfer from one side to the other, although the distribution of this LLT between front and rear wheels can be varied.
~~~~~~~~~~~o0o~~~~~~~~~~~

SUSPENSION LINKAGES
====================

(RW quote)
"In my concept I wanted to use a front and rear mumford link ... to connect a pair of torsion z bars front to rear"

That could be done, BUT (!!!) it is important to remember that the ends of the Z-bars MUST BE bent in opposite directions (otherwise it is a U-bar). So, picturing an end view of the linkages, if the front Mumford rockers are in their "normal" orientation, then the rear rockers MUST BE upside down. This puts one set of rockers quite low down, and may cause problems with ground clearance. Some draft layouts would be necessary to see if it can all be fitted into the space available.

Note that for FSAE or F500, the lever arms at the ends of the Z-bars only have to be about 2" long to give adequate suspension travel. In terms of stresses, the Z-torsion bar could be about 1/2" diameter 4140 steel (x wheelbase length), or even thinner if using proper spring steel.
~~~o0o~~~

(RW quote)
"would the beam axles then act as an theoretically infinitely stiff "end-pair" leaf springs"

No. The Mumford link rigidly constrains axle-lateral-motion relative to its virtual RC, while offering no resistance to axle-roll about that point, or axle-bounce (=axle-heave). So you would have to add a central coil spring, between beam and chassis, to control axle-bounce. It is possible to control axle-bounce with non-linearities of the Z-bar lever arms (eg. by giving them rising rates), but that might introduce other problems (eg. non-linear LLTD).
~~~~~~~~~~o0o~~~~~~~~~~~

DAMPING
========

(RW quote)
"F500 cars are mandated by rules to not run hydraulic dampers of any sorts. They are forced to run polymer pucks ...
If an interconnected double beam could utilize polymer dampers it would easily cut 5000 dollars off the the cost report ...
Please comment..."

The main point I was making on the "Damper Histograms" thread was that the importance of dampers is highly over-rated. Expensive (eg. 4-way adjustable) dampers are "crutches" for badly designed suspensions, namely suspensions that have "stupid" springing. A moderately clever suspension, such as one with interconnected springs, can manage with very little damping.

A most important thing to know about damping is that IF the springing has a low rate, then the damping also only needs to be low. So, Critical-Damping ~ Sqrt(M.K), and thus for given mass M, lower stiffness K means less damping needed.

Modern racecars need lots of damping because of excessively stiff springs, a consequence of stupid spring layout, and aero loads through the springs. With aero direct to the wheels, and interconnected springing (which allows different rates for the different modes), the dampers can be very soft. Even with normal "spring-at-each-corner", but with beam-axles, the springs can be soft ('cos no camber change), so again the damping can be low.

I would go so far as to say that the Twin Beam concept would run adequately with old-style friction dampers. That is, just a small amount of frictional stick-slip "Coulomb damping" would be enough to suppress any resonant bouncing. Cheap mountain bike dampers would be more than enough. Internal hysteresis from polymer pucks may also be enough (depending on compound?).

One way to get a feel for this is as follows. Drop a well pumped up ball (soccer, basketball, etc.) from chest height onto a smooth hard surface. It will bounce almost back into your hands, and then keep bouncing for a long time. This is a curious oscillating system (zero rate spring for a long time while in the air, then variable rate spring for the almost negligible time while on the ground), which has very little damping.

Now drop the ball onto a surface with a few millimetres of water, or loose sand, covering it. The ball barely gets off the ground on its first bounce, and stops shortly thereafter. It only takes a little bit of energy dissipation (ie. damping) to kill the oscillation. This damping doesn't have to be in linear proportion to velocity (as per usual analysis), or even continuous.
~~~~~~~~~~o0o~~~~~~~~~~

SOFT TWIST MODE
================

I stress that the big advantage of both the Z-bar and Twin Beam concepts is that they allow the car to have a soft twist (=warp) mode.

The Z-Bar allows a completely soft twist mode, regardless of other suspension characteristics. In the case of the Twin Beam, both twist and roll modes have equal stiffness, and likewise heave and pitch. However, the fact that body heave, pitch and roll have no effect on wheel camber means the car can be soft in all four modes. This means only soft dampers are required, and also the handling balance is less affected by twist in the roadway.

By comparison, conventional suspension cars (ie. wishbones with spring-at-each-corner) are screwed. They must have stiff springs and thus also dampers, or else they suffer too much body-roll and thus camber change, or they must have stiff ARBs and thus LLTD changes over uneven ground, etc., etc.....
~~~o0o~~~

(Harry quote)
"The thing is that I have a hard time convincing our faculty to go "low tech" (beam axles)...
Actually I will have some of our team members do some quantitative analysis on gains/losses on a "beam axle" car..."

Harry,

From a rational analysis, and for a relatively smooth track, beam-axles are far better than a conventional suspension (as explained above).

The main disadvantages of beams are;

1. Small increase in unsprung mass. Of negligible importance on smooth tracks, and countered by the softer springing possible (stiffly sprung cars have unsprung-mass ~ total-mass!). Even in off-road racing there are many fast beam-axle trucks that suggest this can not be too big a disadvantage.

2. Fashion! If beams weren't around forever, and someone just invented them, then they would be heralded as the greatest advance in circuit racing, ever! (Well, that's the typical hype. http://fsae.com/groupee_common/emoticons/icon_smile.gif) For example, there have been many complicated "camber compensating" wishbone style suspensions that have been patented over the years, but mostly they do nothing more than what a beam does.

I really think that the argument is similar to bi-planes vs mono-planes in aeronautics, with current suspension designers insisting that "Bi-planes are clearly far superior. So much stiffer, lighter, more adjustable, blah, blah, blah..."
~~~~~~~~~~o0o~~~~~~~~~~

AERO RULES & WHEEL PODS
=========================

If ever there was a good example of the failed education system, mainly from the neglect of teaching Euclid, then this is it.

The FSAE aero rules were either written by someone who deliberately wanted to leave open the option of arbitrarily banning any car the judges didn't like, or else they were written by a complete imbecile!

(Quote from Rules.)
"ARTICLE 12: AERODYNAMIC DEVICES
B12.1 Aero Dynamics and Ground Effects - General
All aerodynamic devices must satisfy the following requirements:
B12.2 Location
B12.2.1 In plan view, no part of any aerodynamic device ... blah, blah, blah..."

What (TF!!!) is an "aerodynamic device"??? Nowhere in the rules can I find any attempt to DEFINE this crucial term!

Almost everything on, or even in, the car might be considered an "aerodynamic device". The wheels, engine, roll hoop, car's nose, driver's nose, etc., all have some aerodynamic effect. In F1 Max Mosely banned Renault's inertial dampers (a simple mass-spring inside a sealed container!) because they were "movable aerodynamic devices".

Really, someone needs a thorough arse-kicking..... http://fsae.com/groupee_common/emoticons/icon_mad.gif

And the craziest part of all this is that wheel pods improve both safety and fuel efficiency!
~~~o0o~~~

Enough for now. I've got to cool down after that last one...

Z

Quote:

---

The main disadvantages of beams are;

1. Small increase in unsprung mass. Of negligible importance on smooth tracks, and countered by the softer springing possible (stiffly sprung cars have unsprung-mass ~ total-mass!). Even in off-road racing there are many fast beam-axle trucks that suggest this can not be too big a disadvantage.

---

If you weigh the wheels, tires, hubs, hub carriers, brakes, and driveshafts, the suspension location links usually end up being a very small fraction of the total final unsprung weight.
A beam axle does not have to be an actual beam, just some suitably light and rigid structure to perform that function.
I am not convinced that the increased unsprung weight argument is as bad as most people assume.

The ADFA car had a full weight audit of the car and all components. I cant remember the figures exactly but the front unsprung was approximately 29kg and the rear 28kg. In comparison to previous ADFA cars with A-arms front and rear, this was only marginally heavier. And in comparison to sprung vs unsprung ratios, it was comparable with many other well performing cars running independent systems.

Z,
You are crazy. I like you

Z,

Thank you for the response. I am going to go ahead and model up my ideas with some decent detail. I am going to start referring to the Z-bar mumford link as the "Zumford Link". As for a rough idea of what that will be I am looking at modeling non parallel torsion bars (ala packard suspension)where the bars are closer together in the front and fan out toward the back. The mumford rockers will be of normal layout which means the are elevated a little bit above the lowest crossmember of the main roll hoop and bulkhead. The opposed lever arms will then sit directly under the rockers and connect into the point where the pullrods (i.e lateral force members) of the axle attach to those rockers. So the front lever arms pivot on the torsion bars inside of where the two pullrods attach to the rockers whereas in the rear they are on the outside of the pullrod attacheents.

Rob,

Re: Z-Bar/Mumford Links
=======================

Oops, I didn't think my above answer through properly (under Suspension Linkages). http://fsae.com/groupee_common/emoticons/icon_frown.gif It won't work as stated!

In fact, the Z-bars will only provide anti-heave springing, and only one bar is needed, though two will double the stiffness.

The problem is that the Mumford outer diagonal links only provide "lateral" control of the beam (wrt the virtual RC), and they don't allow individual "vertical" control of each side of the beam.

However, you can still use two longitudinal Z-bars as you explained (closer together at the front than rear) and just connect them to the beams with short links. (Edit: These links must be more vertical than the Mumford diagonal links!) These two Z-bars will control body heave and roll motions.

Furthemore, you can fit a spring between one Mumford rocker and the chassis (resisting rotation of the rocker), and that will control axle-bounce at that end of the car (ie. this would be instead of a separate coil spring at axle centre). Doing same at front and rear gives body heave and pitch control.

Edit: Note that:
1. When the axle rolls wrt chassis, there is no movement of the Mumford rockers wrt chassis (ie. they could be welded solid to the chassis).
2. When the axle bounces (=heaves) wrt chassis, both rockers rotate equal amounts but in opposite directions wrt chassis (ie. they act as if they are two gears in mesh).

All this is proof that a picture is truly worth a thousand words!

Z

So you could have a heave/pitch spring attached to both mumford rockers....

Z,

I was just suggesting the Zumford Link as a lateral control of front and rear beam and z bar interconenction in one clever Chapmanesque device and not as a complete form of beam location. I was also looking to use said mechanism to tie into some sort of rotary damper to tie inline with the Mumford rocker pivot(s) such as a cush drive works on a motorcycle in order to eliminate any need for hydraulic dampers. A rotary way that a F500 achieves linearly. I realize that front and rear beam would still be unconstrained longitudinally. I started with "how do i z bar a double beam" without other layout concerns as my first "wouldn't it be cool if". I was under the impression that two z bars were needed but now if I understand correctly we only need one.

I started drawing and found there there are a couple driver/engine placement combinations in reference to wheelbase along with many different beam and beam control. Some of which were quite innovative and packaged neatly such as the one that places the rear beam 2.5 inches rearward of the main roll hoop while the engine lays underneath the drivers legs. This led me to have questions regarding these linkage arrangments along with what would be an ideal canvas to work with to later add aero.

I dig your concept but would like to explore some other possible methods to achieve the same effect. That being a double beam car with aero but with the addition of suspension interconnection to reduce expensive componentry and more effective platform for aero.

Please review these statements to make sure my understanding is correct. Assume A/B=1 for these and that lever arm A and B connect to the middle of the beams.


1) A beam connects each end pair together so only one z bar(as opposed to two in an IFS/IRS car)is needed because rotation of chassis to one beam is equally and oppositely reacted by the other beam to keep the chassis level. If I lift up on the LF by 1 unit then RF,LR,RR will push down by 1/4 unit which will effectively make a heave of 1/4 unit? ***One wheel lift skew effect***

2) A single spring/damper setup on the end pair beam will affect only the compression of that beam so the spring/damper on the rear is for acceleration squat and the front is for braking dive. Without these, if i lift up on LF and RF by 1 unit then LR,RR will push down by 1 unit which will effectively make a pitch/dive of 1 unit? ***End pair pitch effect without spring/damper***

3) A beam connects each end pair together so only one z bar(as opposed to two in an IFS/IRS car)is needed because rotation of chassis to one beam is equally and oppositely reacted by the other beam to keep the chassis level. If I lift up on LF,LR by 1 unit then RF,RR will push down by 1 unit which will effectively make a roll of 0 degrees? ***Side pair compression roll effect***

I read you correction. So if I ran a single z bar with lever arms that attached to a the beams in the center and run a spring/damper at each end again attached to the beams in the center I would be able to control all spring and dampening through the centerline of the car (spring damper mounts and torsion bar bushing mounts) and have my suspension interconnected? I like the symmetry and ease of this. Would there be any other good reason to run more than one z bar to pullrods coming off of ends of the beams. Beam bending from spring forces? Your comments of mumford rockers not doing anything in roll confuses me. You can see it move with one wheel bump (roll) in this video...

http://www.youtube.com/watch?v=jIiEV0DILBw

I am rather unfamiliar with aero requirements and wonder how that effects the freedom of design if the intent it to eventually put a single piece aero tray that has been claimed to offed the most downforce. Both designs have the minimum wheelbase of 60" and a track of 48" One has the beam axle 2.5" behind the main roll hoop plane and the other is 15". The crossbar for the main roll hoop is 1" ODx 24 inches wide and currently 3 inches to tube centerline from the ground (2.5" ground clearance) The rules madate how far the tunnels of the diffuser can go behind the rear axle. I have no idea the hows and why of how fast the tunnels grow but I was wondering if you or anyone could comment if that it doesnt leave enough room for future tray design versus the less choked up rear axle centerline.

Rob,

As I said, a picture is truly worth a thousand words, and a simple sketching facility here would make all this much easier. http://fsae.com/groupee_common/emoti...n_rolleyes.gif

Nevertheless, let's start with the Mumford link, as shown in your link above. This has;
1. The "chassis".
2. "Two rockers" pivoting about longitudinal axles fixed to the chassis.
3. A "central link" connecting the two rockers, such that the rockers always rotate equal and opposite amounts wrt the chassis. Looking at this a different way, instead of this central link, each rocker could have gear teeth near the car centreline that mesh with the teeth of the other rocker. Structurally, the central link is probably better than teeth (less backlash, etc.), but for understanding it might be easier to imagine the two rockers as "geared" together.
3. "Two diagonal-links" going from the rockers out to the beam-axle ends.
4. The "beam-axle".

You say "Your comments of mumford rockers not doing anything in roll confuses me. You can see it move with one wheel bump (roll) in this video..."

What you are seeing is indeed "one wheel bump". But, importantly, the left-wheel-only-bump of say 2" equals axle-bounce of 1" (ie. both wheels up 1") plus axle-roll of 1" (ie. left up 1" and right down 1"). So what that video is showing is the rockers moving as a result of the axle-bounce of 1" (ie. the height the centre of the axle is moving wrt chassis).

To further clarify this (hopefully???), imagine the rockers welded solid to the chassis. Now there is a four-bar linkage consisting of the chassis, two diagonal-links, and the beam-axle. The beam-axle and chassis can only move wrt each other by rotating about the "Instant Centre" found at the intersection of the two diagonal-link centrelines (these being "n-lines", or lines of "no relative motion"). This IC is thus the "Kinematic Roll Centre" (for this simplified 2-D analysis).

So "no rocker motion" = "pure roll".

Now imagine the axle moving in pure bounce (both wheels up or down equal amounts). The diagonal-links pull equally on their respective rockers, and the rockers rotate equal amounts but in opposite directions ('cos geared together).

So if you want to provide a spring that controls ONLY axle-bounce, you can do so by resisting this rocker rotation. This could be your "some sort of rotary damper to tie inline with the Mumford rocker pivot(s) such as a cush drive works on a motorcycle", or any other arrangement that resists the rotation of the rockers. Note that you only have to control one rocker, because they are both linked together, but providing a torsion spring to both rockers spreads the load structurally, and may be neater (?).

All the above only refers to one end of the car (ie. front OR rear). But if you provide such an arrangement (ie. Mumford link with spring controlled rockers) to both ends of the car (F AND R), then you have control of body heave and pitch. This is similar to the "Z-Bar Sketch" top-left WITHOUT the two side "centre-pivot-leafsprings". So the "sprung-rocker-MLs" replace the "coils-at-beam-centres", plus providing lateral control, and perhaps being better structurally because less "beam bending".

BUT, you must still control the body's roll mode, without adding twist stiffness!

A single centreline Z-bar connected to the beam centres would ONLY add body heave stiffness/control. When I said "you only need one of these" (connected to the ML rockers) I meant that one bar adds heave stiffness, and the second just adds even more heave stiffness. Importantly, neither adds any roll stiffness/control (in fact, they add NO stiffness to ANY other mode).

So, YOU STILL NEED TWO LONGITUDINAL Z-BARS with their ends connected to the outer end of the beams (say, via short vertical links). These give body heave and roll control. The extra heave control is not really needed, but to get independent control of ONLY the roll mode takes a different mechanism, possibly more complicated.

There are other solutions possible (eg. "Balanced Suspension", which gives simple and completely independent control of all modes) but that is another very long (!) story, and not really necessary for the smooth tracks of FSAE and F500.
~~~~~o0o~~~~~

You say, "I realize that front and rear beam would still be unconstrained longitudinally."

Yes. But if (?) you want to use something like the side-pair Centre-Pivot-Leafsprings (= body heave/roll Z-bars) in the Z-Bar sketch (top-left), then these can be used for longitudinal control. Braking torque reaction of the axles would also be needed, but even this could be incorporated into the side-pair CPLs.

In fact, that top-left sketch, with peg-and-slots for lateral beam control, has a lot of potential for a very simple, smooth track, short wheelbase racecar.
~~~~~o0o~~~~~

You ask, "I am rather unfamiliar with aero requirements...
I have no idea the hows and why of how fast the tunnels grow but I was wondering if you or anyone could comment if that it doesnt leave enough room for future tray design versus the less choked up rear axle centerline."

From my point of view, tunnels are NOT necessary. A completely flat floor will work IF you "drive" it right. That is, a separate "flap", or "wing", or "aero surface", at the right distance from the rear edge of a flat floor will work just fine (like each wing on the Twin Beam Wing sketch). Similar "aero devices" at the front and side edges of the floor will make it work even better! This requires some original thinking, but there are huge gains possible. http://fsae.com/groupee_common/emoticons/icon_smile.gif

One aero requirement that should be met (I guess?) is that the aero surfaces should remain a reasonably constant distance from the road. Since the road is likely to have some small "twist" in it, I reckon it may be beneficial to let the periphery of the rectangular aero-undertray also twist with the road surface.

The Twin Beam Wing does this, in the sense that the two beam-wings follow any twist in the road. Likewise, the top-left Z-Bar sketch does this, if the aero-undertray periphery is fixed to the two beams and two side-pair CPLs.

(Edit:
Also, the top-right "Z-Bar" sketches (p4) show how the undertray can be divided into five rigid pieces and still conform well to a twisting road. The floor of the chassis forms the central diamond shaped piece, and four triangular corner pieces pivot off the edges of the central diamond to complete the rectangular undertray. The pivots (ie. hinges between diamond and corner pieces) can be low friction, so the whole undertray is very flexible and adds no twist stiffness to the suspension. This also makes accident repairs easier - just replace the damaged corner.
End Edit)

~~~~~o0o~~~~~

Apologies for all the capitals, but this forum definitely needs a simple sketching facility!

Z

All,

A lot of what is being posted about interconnecting corners in varying manners has already been or is being done. However, it's being done hydraulically. Think UWA.

TestDriver,

"Already been done"?

Let's not forget the "world's cheapest car", the Citroen 2CV, designed in the 1930s with very effective mechanical side-pair interconnection.

I am sure motorsport will catch up one day.....

(Not sure about Detroit. http://fsae.com/groupee_common/emoti...on_biggrin.gif)

Z

Z,

I'n not getting something here. You say "A single centreline Z-bar connected to the beam centres would ONLY add body heave stiffness/control." and "So, YOU STILL NEED TWO LONGITUDINAL Z-BARS with their ends connected to the outer end of the beams (say, via short vertical links). These give body heave and roll control. The extra heave control is not really needed..."

Let's say that the front axle bounces by 1" the rear goes down by 1". This to mu understanding represents a pitch motion (heave would be the other way round). When the front axle bounces by 1" the Z-bar would like to push the rear axle down by equal amount (if A=B). So how a Z-bar connecting front and rear axles contributes to heave/pitch stiffness? Am I missing something here?

As I see it we have two separate issues to be resolved:
1st is axle location both longitudinal and lateral.
2nd is control body movements. If you can incorporate lateral control to motion control or something, you end up with fewer parts->lighter. The real issue to me right now is which modes you want to control, why and how.
On a beam axle car I would not bother having some roll and pitch, as they do not affect tire path or tire loads that much. It might be upsetting for the driver a little, but I think that those modes should not be (very) stiff, they could be left somewhat soft.
The same applies with warp mode (as soft as it gets) and bounce (stiff enough for the chassis not to bottom out hard on axles; maybe rubber bumpstops?). Actually the only movement I would like to limit somehow is single wheel bump. Any thoughts on this?