Calculating PID Constants for Motion Magic

[joemost]

Our Arm has a small oscillation that we are struggling to get rid of!

Motor Controller Closed Loop

Following the Motion Magic tutorial provided by CTRE. One thing I noticed is we scaled our encoder (by adding a coefficient) so our encoder is basically true to 1 degree.

Should the P,I,D values also be scaled by this? I’ve noticed my gain values such as P would be greater than 1 if this was the case.

Or should they remain true to native encoder units in their measurements? I know the D value is supposed to help remove the small oscillation, but whatever value we set in seems to not help.

PS: CTRE used to have that motion magic arm example up on github, is that now gone?

[joemost]

also tagging @Jacob_C

[mendax1234]

Stryke Force Talon SRX Motor Training Course Dec 2017 – Chapter 8 - YouTube

You’d better look at 2767’s tutorial if you are using CTRE’s motor, like TalonSRX.

OUr team had followed this tutorial and successfully implemented Motion Magic on our swerve.

[MrNick]

Is gravity effecting your arm? Your PID may just be constantly trying to fight gravity. You might want to add an arbitrary feed-forward, which is available with motion magic. The CTRE documentation has two use cases, an elevator (with constant effect by gravity) and a swinging arm (with variable effect based on the position of the arm).

[joemost]

yeah we have that actually! We tuned a feedforward that is cosine based to it’ll vary. I’ve gone through that whole tutorial

Its just some pesky oscillation in one specific spot…

[MrNick]

Cool. It smoothed out our intake and a few other things for us. It’s a nice feature that’s easy to add once you’ve got the rest of motion magic.

Good luck tuning things!