Coefficient of Friction Testing

[DonRotolo]

Data? No. That's lost to me.

The first question we wanted to answer was if 12 wheels were any better than 6. One test was to have a 6-wheel robot and a 12-wheel robot (both same wheelbase and weight) push against each other, to see who would win. At first, the loser was universally the one which spun its wheels first. With extremely careful and skilled control, the 12 could win but the 6 could not. Repeatable with difficulty, but repeated enough times that we went with 12.

The second question was related to whether traction control - to prevent wheel spin - would provide an advantage.

We first needed to find the amount of wheel slippage that would be acceptable, and for Lunacy, IIRC we found that grip vs wheel velocity relative to the surface was somewhat linear - higher speeds giving less grip. We did this by powering up the wheels with a PID loop to a certain speed, and measuring the resulting pull with a scale (think fish scale, but of a higher quality, up to about 40 Lbs).

We then needed to measure the effect of a slip limiter. Using a 5th wheel for odometry, we used a PID loop to limit PWM input to Jaguars such that the slip was some percentage of the robot speed. (I think we settled on 12%, but I can't say why). We then went drag racing, timing the robot over a fixed distance, the driver simply giving full throttle and letting the system throttle it back.

Our final result was that a simple rate-of-change limiter in software was nearly as effective, avoiding a lot of hardware, and that's what we competed with.