Robot deviating to the side in straight motion

[weilin]

Yes, checking for extra friction on one side, as others said, is first thing to do.

The second question is: do you have a second PID loop to keep it driving straight in software?

Drive Straight PID Loop

I think this worked. This was for encoder backs, so you will need to change nMoterEncoder] to SensorValue() for OSE’s. // function to run drive motors for specified distance in units defined by WHEEL_DIAM then stop the drive motors // +dist = forward, -dist = reverse. void driveDistance(int dist) { nMotorEncoder[drive_LF] = 0; // reset the ime values to 0 nMotorEncoder[drive_RF] = 0; driveLastError = 0; // update driveLastError driveTarget = fabs(dist/(WHEEL_DIAM*PI) * ENCODER_TICKS); // …

Drive Straight PID's

Using PID to drive straight is a problem that can be solved with a 2-DOF controller (two degrees of freedom). A drive train has two degrees of freedom (x and y axis) meaning you can readily control it with two PID controllers. Think about what happens when you want the robot to turn left 90 degrees, for example. The robot has subtractive power to the left side of the chassis and additive power to the right side. As the robot approaches the target angle, less and less power is sent to either sid…

If you have well tuned 2-DOF PID controller, then you can disconnect one of two motors on one side and it will still keep the robots driving straight.

If friction on both sides is the same then accumulated Integral value for the second controller is going to be around zero.

But if you print it to LCD and see it walk away from zero - that will tell you that one side has more friction or some other issue.