Beam axles

[MalcolmG]

Originally posted by oz_olly:

Next year we will follow a similar concept using but taking the track width down from 1250mm to 1050mm whilst maintaining the same cg height to track width ratio to ensure the weight transfer is the same. By reducing the track width in the rear the engine ancillaries can be mounted further to the back. The smaller WR450 engine (over GSX-R 600) will allow the driver to be reclined further and seated further back.

I like your thinking

[thewoundedsoldier]

Originally posted by Mike Cook:
I think the main reason not to do this is because one wheel disturbance affects the other wheel.

If you count one wheel sweeping a larger radius than the other wheel as a disturbance, then I think you're right!

Judging from what I've seen on other cars and how our car is shaping up, I think that system compliance allows just as much roll relative to the chassis as an independent setup would. I've gotten to the point with the design where I don't even care what the numbers look like anymore because there is so much damn compliance in every system of the car. Tested numbers are gonna be the only way to prove anything. This seems especially true of the rear axle debate.

[thewoundedsoldier]

Oz, your setup for next year sounds very interesting. We're a formula-hybrid car, so we only have to package a 250cc engine (nee. Ninja or CRF). This allowed us to tighten the back track down to 40". The reduced track really helped with torsional strength of the axle, so we are no-joke trying to run our system with a piece of 1.25" OD x 0.095" wall thickness 4130 tubing.

I believe we spoke a while back about a failure you experienced with a solid axle due to torsion? I cant remember if you sheared drive pins or what, but I'd be very interested to know what happened and what your axle looks like this year. Every time I walk through our shop and see that piece of chromoly I giggle inside. Hopefully it works =/

[oz_olly]

We've never had any drive axle failures. Our biggest failure was a front hub that was grossly understrength for the cornering load case. The hub flanges each failed and the wheel departed company with the car. The wheel almost jumped a fence onto a busy road but luckily it ran out of steam.

At the moment we use 4340 quench and tempered drive shafts with the TRE tripods as it is a de Dion style beam axle. The beam has a slot down it's length to make it torsionally flexible so it's not kinematically over constrained.

Malcolm, it's easy to see why you like my thinking as you were the inspiration behind the idea. I remember talking to you about weight transfer amongst other things at the Optimum G seminar. Then I read your team's article in the Race magazine which locked down my plan. The concept with the current car was large track width and beams seeking high mechanical grip on smooth surfaces aka Hoppers Crossing. The best part of the new concept is the geometrically faster route through slaloms. Just means we have to be as anal about cg height as weight (but we should be anyway). The CAD model has a CG plane in it and any component placement above it requires the approval of the Technical Director.

Have a look at this link:

http://www.fsae.unsw.adfa.edu.au/car.htm

There are some reasonable pics of our car but nothing square on from the front or back. The page is an exact copy of our design report. We figure we're not competitive enough to really worry about other teams seeing what we wrote. I think it's in the spirit of the competition to throw it out there, who knows we might even receive some feedback either way.

Cheers

[oz_olly]

Bump... Now that my post has finally been approved.

[thewoundedsoldier]

Hmmmm for some reason I thought you were someone else, using a SBA rear design. My bad.