Transmission Design Help

[JVN]

Originally Posted by JoelP

Wouldn't the width of the wheel have a much greater effect on its traction rather than the diameter? Perhaps by saying a "bigger" wheel they are referring to the width of the wheel. And if you look at it using basic kit wheels, the bigger wheel, the pneumatic wheel would be thicker, have a larger diameter, and have greater traction due to its tread, than the smaller, smoother skyway wheels.

Width DOES play a role in traction, but not a major one.
Again, because we are dealing with non-perfect surfaces the Frictional Model of F=mu*N doesn't quite work. As a result of this, surface area does affect traction.

How much does it affect traction?
I don't really know. This is something you should play with, and get some experimental data for. When it doubt, test it.

So JVN, if you don't believe it plays a huge role, why did you use 1.5" wide wheels on some of your robots?
Well, here is why:
Assuming a wheel has a known force that is going to be transferred to the carpet (has a set Normal force applied to it, with a set torque, set coefficient of friction) a wider wheel will disburse that load over a larger area. As a result of this disbursement, tread will wear slower (so you won't have to replace wheels as frequently) and it will be less likely to cause carpet damage.

Also, because I don't totally know the nature of "how much traction increase will a wide wheel give you" I hedge my bets, and go with a medium width wheel. Yes, I'm a cop-out.

Other factors to consider?
The wider wheels will likely cause increased turning scrub. This must be taken into account when designing the wheel-base layout.

-JV