Thanks Mark.
We do clearly have a small speed difference between black and grey as well. Much harder to measure though.
I’ll measure under load and see what I get.
I don’t think the offset is linear. I just tried my code today with the speed being divided by two and the robot drives much straighter. I haven’t had a chance to test PID yet. Electronics guys are still trying to get encoders connected.
I should have mentioned this much earlier. How much wire do you have feeding the two sides of the robot? A frequent problem is inches feeding one side of the robot with feet feeding the other side. If you are using #12 to feed the drive system, you can accumulate significant loss in the wiring. It amounts to about 0.2 volts per foot at near stall current for CIM motors. Remember you have to count both the black and red wires to arrive at the correct calculation. It is for this reason that I recommend a central location for the PD to balance the wiring.
all wiring runs follow the same path, we had the problem you are describing last year