paper: Shooter Wheel Speed Control

[Tom Line]

Success in one area, and failure in another.

We've changed where our encoder is mounted and subsequently doubled the count rate. Our biggest problem appears to be the use of the Labview (and therefore WPI) Encoder getrate to get the instantaneous rate. The getrate returns horribly noisy data, presumably because of a very short measurement period.

We now calculate our own getrate, and that has completely smoothed the encoder input signal. This, in turn has smoothed both our PID and our bang-bang. We can switch back and forth with the click of the button. The best tuning of the bang-bang (combination of filter and slew rate) nets us approximately +/- 60 RPM. Our PID is around +/-25, which I'm very happy with. The bang-bang gets up to speed is about 2.0 seconds. The PID is about 2.5 seconds.

We do still see the same slow drop off from a high speed to a low speed with PID. However, we don't ever have an issue with that because once the fire button is pushed the drivetrain is zeroed and the pneumatic brakes are engaged. That's the polite reminder to the driver not to try driving while we're shooting

This is a 400% improvement in our RPM repeatability from shot to shot. We'll see if it translates on the field at nationals. Thanks to Ether and Chris for keeping the ideas flowing.