2012: Tuning the Jaguar's Speed Control PID Loop

[mjcoss]

Worked on this last night to try once more to tune the PID loop for speed control on our shooter motors. Unfortunately, I don't seem to be able to get a stable system over the entire range. Between 500 and 2000, I see pretty stable values, but system starts oscillating as I move up between 3000 and 4000. 4000 is close to the maximum that the motors can do.

I applied the method mentioned here where I got a stable min P @ 50% set point, then added I to get to the set point. Is there no reason to add the D term is is the Jaguar PID just to flaky?

I'm not sure whether to keep tinkering with this or just declare it stable enough.

---Michael J Coss

Originally Posted by Mr. Lim

Some anecdotal notes to share with you: we're using 256 ppr Greyhill 63R series encoders, directly attached via surgical tubing to a ~6" wheel. We run them from 200-1800 RPM.

The vanilla PID implementation in the Jags is not well-suited to speed control PID. Tuning them using traditional methods as you have been may be futile. Hence the reason why I started this thread in the first place. Many of us have been down the same road you have, and have been left bitterly disappointed in the results.

The first two posts in this thread are exceptionally valuable IMO, as they are workarounds on how to massage the Jag's limited speed control PID into something workable.

If you insist on using more traditional PID tuning methods, I can suggest method #3, which is a more conventional DOES appear work for systems with very little resistance or changes in dynamics (i.e. a free-wheeling shooter wheel).

Start with 0 for all terms. Increase P until you reach approximately 50% of your setpoint. Adjust it down until you find the P value that results in the least amount of fluctuation in speed. You may need to reduce the P significantly to get a very stable value. You should be able to get ~1% deviation from wherever your speed happens to settle. The important thing here is that your output rpm remains as rock solid as possible, and you've pushed it as close to 50% of your setpoint as you can get it.

Now bump up your I term 0.001 at a time until your system finally achieves your setpoint. Use the least amount of I possible such that your system can reach it maximum speed.