Robot veers left when driving backwards!
 

When we drive forward it drives relatively straight. Backwards however it veers of to the left pretty drastically.

Any ideas?

In the code (we are usign FIRST Drivetrain) we set one set of motors to (254-p1_y) because motors are on opposite sides.

We re-calibrated speed controllers but that didnt help either.

Any suggestions welcome.

Re: Robot veers left when driving backwards!
 

if you want to code a fix, take the faster side and multply by something like 0.75.

sooo:
if (pwm11<127) //only for reverse
{ pwm11= (pwm11-127)*0.75 +127; }

that oughta work. i can never remember if pwm11 is left or right, you may have to change it. Let me know how it works.

Re: Robot veers left when driving backwards!
 

I would look at the drivetrain. Last year out bot when we would drive forwards would go to the right, and veer to the left when going back. It would make a 10 point turn just by going back and forward.

I thought it was the motors having more power in the forward direction than in the backward direction, but it turns out that the CIMs have the same power forward and backward, and it was the drivetrain that was doing it.

Re: Robot veers left when driving backwards!
 

almost all motors have a powerful direction and a less powerful direction. for example, the van door motor has 30 Nm CCW and 34 Nm clockwise at at the same # of RPMS. are you motors on opposite sides going different directions?