PIDs out of control

[gpetilli]

Originally Posted by wildaburk3160

After getting our drive system running, we've run into some trouble with our PIDs.

We have four independent steering modules each with a potentiometer, all run by PIDs. We've gotten them successfully working as a crab drive/ being able to rotate.

However, one or more motors will occasionally rotate, spinning out of control without any input from a driver. I'm not sure what would cause this issue if, for the majority of the time, the code does what it's supposed to just fine.

I'm at a loss as to what would cause this issue. Any ideas?

Unexplained failures have a habit of returning at the worst possible moment - yes it is an issue. One common intermittent stability error is as you rap around from 360 to 0 degrees (and 0 to 360), you may introduce a toggling of the sign and magnitude of the error signal. I would start looking at the way you wrap around the circle.

To Ether's point, I assume you are using one of the newer "absolute encoder" http://www.andymark.com/product-p/am-2899.htm for the feedback? If not, you should consider something similar that will not be damaged if you over rotate. Again, this device will have a "discontinuity" at the 360->0 point that needs special consideration.