UTAS build thread

[Jonny Rochester]

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]

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]

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]

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]

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]

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]

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]

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

[Z]

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

[Z]

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