Traction control: How do I tune a PID controller with variable gain?

[Tom Bottiglieri]

Originally Posted by windell747

Thank you so much for your responses! Here is more information of our setup.

We are using 4 encoders: 2 on the gearboxes and another 2 on follower wheels. We are also using Labview and its PID libraries.

My approach is to allow a certain amount of slip upon launch by letting the driver command the motors directly, then if the slip ratio goes higher than a specific value the traction control will activate and motor commands will come from the traction control part of the code to bring the slip ratio down under that margin. Once it is under that margin, then the driver can control the motors directly again.

When the robot is at a stop (gearbox velocity=slip ratio=0) the traction control is forced to be off.

Anyways, how does this approach sound? Am I on the right track? I would like to keep my code as simple as possible so that I can arrive at a traction control solution the fastest.

I attached a screenshot of my code.

FYI: PS=port side, SB=starboard. The traction control enable controls a select with the joystick feed in the false case and the traction control feed in the true case.

Your slip will be out of the threshold most of the time with the current algorithm. Unless the joystick values are ramped or rate change limited, you will experience jitter as the slip passes in and out the threshold. This will happen very often. (The slip will drop, wheels will spin out, rinse, repeat.)

I would run the joystick through something like this http://www.chiefdelphi.com/forums/sh...55&postcount=3 before pumping them into your algorithm.

You can overshoot on the ramp gain a bit to allow for a bit of slip in launch, and the slip threshold should catch exceptions when you run into stuff on the field.