[WheelWatcher] Help with tuning

[<rob.stehlik@xxxxxxxxxxxx>]

Hello,

I have just installed a couple WW02's on my robot which has custom wheels 
and motors. I am currently trying to get the advanced velocity and position 
control code working (I am using a PIC 16F877A with CCS), but am quite 
confused about the way the feedback controller is tuned. I am used to 
adjusting gains for P, I and D terms, but this code seems different. 
Currently I have it so the code functions properly, but the robot's 
movements are not well controlled. IE when driving in a square, the robot 
always overshoots, especially in the turns, and sometimes does not recover. 
Many times the robot will get stuck oscillating around the target really 
slowly. The positioning accuracy is terrible.  I have tried adjusting the 
divisor in the integral calculation, as well as the acceleration value. And 
I played with the deceleration term (was originally 150). After running 
tests for several hours, the robot performs a little better, but it really 
leaves a lot to be desired.
So, I guess my question is what approach should I take when tuning the 
controller? Which parameters should I vary? And considering my robot is 
quite heavy and fast, is there anything I should keep in mind when adjusting 
the parameters? Is there a way to set a minimum PWM duty cycle? Because of 
my robots weight, it does not move well at slow speeds.

I appreciate your help,

Rob