Problem with KitBot: Motors move at different speeds

[GeeTwo]

Originally Posted by PaulEleven

Hi y'all,
So we just loaded up an arcade drive program onto the kitbot, the programming is correct and right now when the bot moves forward, the right side spins faster, when it goes backwards the left side moves faster. We thought it might have been the tension between the two plates and we loosened the bolts, but it is still doing this.
The motor controllers are paired up with y cables so we only have a left and right output.
Could it be possible that somehow the cims move faster in one direction comparing to the other?

If none of the other things mentioned help (and I expect that they will; all seem more likely than any of these), I have to wonder if somehow there's a drag or misalignment that makes things want to rotate to the left.

The KOP shouldn't have this issue, but the easiest way I can imagine this sort of behavior is if the four wheels that are supposed to make contact with the carpet at any given time aren't in the same plane. Go forward: it'll rock back, put weight right, and you'll get traction on the right. Go back, it'll rock forward, and you'll get traction on the left. I suppose this effect could also be caused by a saddle-shaped floor.


It probably won't make a difference if you're using the KOP wheels that are exactly in the same line, but as we've swapped out for omni dualies, we were careful to make sure that both outboard belts were on one side (rear) and both inboard belts on the other (front) to avoid anything peculiar. Also check that the opposite faces of the chassis are the same length and that the frame corners are square. An off-center COG shouldn't cause behavior like this, but it's worth checking if you're still trying things at this point.