paper: Shooter Wheel Speed Control

[Tom Line]

Originally Posted by Chris Hibner

When you say +/- 100 RPM, do you mean that as: a) noise in the measured RPM, b) slow oscillations of 100 RPM, or c) your steady state (highly filtered) RPM settles at 100 RPM from your target?


We run the unfiltered encoder speed into the bang-bang controller and the speed noise is on the order of +/- 200 RPM at that stage. Once the shooter reaches it's target speed, our heavily filtered encoder speed reads about +/- 15 RPM of noise, but the unfiltered encoder speed going into the controller is still its usual +/- 200 RPM. We keep 2 versions of the speed in our software - one unfiltered to use for input to the controller, and one heavily filtered to use as the input to our "okay to shoot" logic.

Important note: we do NOT rate limit the PWM command to our Victor speed controller. We send it a steady stream of 1.0 or 0.0.
Another important note: our shooter wheel has a fair amount of inertia.

Chris, now you've got me really really curious. How are you filtering?

The only filtering I'm used to is floating average with X number of samples. However, that introduces significant lag. Are you using something more exotic?

I've read up on IIR and FIR, and frankly I haven't found a decent English-language explanation of what they DO.