I'm trying to get PID speed control of the Tetrix motors to work reliably and I'm having alot of weird problems especially at the top speeds.

There are lots of random jitters and sometimes it goes completely crazy locking in at full power regardless the power level I give it.

I'm beginning to wonder if it has to do with the "nMaxRegulatedSpeed12V" parameter. Unfortunately, the documentation seems to only refer to the range of values appropriate for the NXT motors.

Any ideas what range of values this variable should have?

I'd imagine its really dependent on the weight of the robot, efficiency of the drive train and battery level.
Has anybody tried to tune this parameter? If so how did you go about doing it.

Are there any other PID parameters that should be looked at for tuning closed loop performance?

The nMaxRegulatedSpeed12V is only used for the NXT-based PID functionality. This function was implemented before it was aware that the HiTechnic motor controllers had their own PID functionality... so this function is currently useless.

There are no user-configurable parameters to the HiTechnic PID functions.

Okay, I was figuring with the "12V" in the name that it was for the Hitechnic stuff since I didn't think NXT uses 12V of anything.

Sorry to hear the built in PID can't be tuned. It doesn't seem to work very well out of the box. Although I didn't expect it to, from my experience PIDs are extremely sensitive to the complete system they are used in, so I figure the weight of the robot or actuator would have a big impact.

At first I thought they were going to work even without tuning, but I keep getting these random twitches and the robot goes into convulsions. This makes them unusable.

Maybe somebody else has had better luck using them on a real robot.

I've finally finished a fuzzy logic engine for RobotC so pretty soon I'm not going to need the PIDs anyway