Drive axle length issues

[willhalt]

Looking for a solution to having different length axles. The differential will not be centered in the frame, because of where the output on the motor is. Anyone have any practical solutions to accounting for torque steer , how to center the diff. in the least complicated manner? I've read the solution is to make the smaller length shafts' diameter bigger, but I don't know how you would begin to calculate that. Any suggestions?

[willhalt]

Looking for a solution to having different length axles. The differential will not be centered in the frame, because of where the output on the motor is. Anyone have any practical solutions to accounting for torque steer , how to center the diff. in the least complicated manner? I've read the solution is to make the smaller length shafts' diameter bigger, but I don't know how you would begin to calculate that. Any suggestions?

[Yellow Ranger]

I believe you would relate a shaft's angle of twist for a given torque with a specific length and inertia. I'd have to whip out the old DMC book...

[Wes Johnson]

http://en.wikipedia.org/wiki/Torsion_%28mechanics%29

[Conor]

Don't waste your time. We dedicated a lot of effort on our '08 car to account for torque steer and finding ways to balance the drivetrain. In the end we were left with two sheared axles a day before competition because of the resulting stress risers that can from the diameter transitions. Luckily we were able to get an entire set made and heat treated within 24 hours. You can try to convince me until you're blue in the face, even if you are a design judge, but I'll take the reiliablity of similiar sized shafts over the minute effects of torque steer (which we never noticed and unless you have the most perfectly balanced car, you won't notice either) any day.

[murpia]

This has been discussed a few times before...http://fsae.com/eve/forums/a/tpc/f/125607348/m/1466038355
http://fsae.com/eve/forums/a/tpc/f/125607348/m/99510106241

and at least one other time if I remember right, you should be able to find it with a decent search.

Regards, Ian

[rjwoods77]

Also something to consider is wether or not you have a diff you will almost never have the axles sharing equal loads unless in a straight but there arent many of those. The real question is where are you trying to target your axle torque steer effects in your driving. I cant really even think of how to conclude that without putting torque transducers on your axles and log while driving a typical fsae event and calculate that versus tire data,weight transfer,etc.

[mtg]

+1 for Conor and rjwoods

The only time there is going to be an induced yaw torque from differing torsional spring rates of axles is the first nth of a second of an acceleration launch until the wheels start to turn. If you are concerned about matching axle spring rates, you should also be matching the torsional spring rates of your tires, wheels, uprights, control arms, etc etc. And that of course assumes your yaw axis is in the center of of car, laterally, of course.

I forgot his name, but the chief of design at FSAE-West this year in the design post-briefing made a fairly profound statement- "start with the simplest possible car, and only add complication when you can justify that you earn more points by doing so". Or something similar. The application here is exactly what Conor said.