Our robot was veering to the left when climbing the ramp. The right side drive stopped working about 2/3 up, resulting an an unplanned U-turn followed by a speedy return to the carpet, after which normal control returned.
Our drivetrain uses two Bosch drill motors, pins removed, shifter ring internally locked in low gear with a spacer we made. The second reduction stage is the 2:1 helical gear set that came in the kit. Our front drive wheels are 9" pneumatics, and we use two 80mm omni-wheels as rear casters.
We spent quite a while checking and changing elements of our drivetrain, trying to isolate the problem.
We checked to be sure the friction was the same on both sides, by manually rotating the wheels and then by free-rolling the robot down the ramp with the power off. No difference observed between right and left, and the 'bot rolled straight down the ramp and continued across the carpet several feet.
We removed and replaced the right side motor controller, with no effect. Then we removed and replaced the right side motor (leaving the gearbox in place), again with no effect.
We checked and rechecked our wiring, our software, our custom electronics – all with no effect.
Finally we tried swapping the right and left 40A breakers. That made the 'bot veer right instead of left.
So we replaced the offending 40A breaker and have not seen the problem since.
Apparently some 40A breakers are more sensitive than others.
Has anyone else seen something like this?