Not smooth Motion Magic Profile

[cpapplefamily]

We are trying to implement Motion Magic on our elevator. We have a RedLine Motor on a 57Sport 80:1 gearbox. The Elevator has some counter balance Constant force springs. For feed back we choose to install a 10-turn potentiometer on one of the idler sprocket shafts that ends up turning ~4.5 rotation trough the travel of the system.

What we are seeing is the motor starting out slow, then jumping to the Cruise Velocity, switching back to a slow speed, finnaly a quick jump to Cruise Velocity before finally stopping at the setpoint. Attached is the plot from the Phoenix Tunner. The Test code is a directly modified variant of your sample code with the Follower motors commented out along with the feedback device changed to Analog and signal phases adjusted accordingly. I also had to comment out the “configMotionSCurveStrength” because of errors. I believe I have the latest install of the CTRE tools but the libraries seem to not be in sync.

Thanks for any pointer or dirrection you can provide.

[ericjanofski]

We had a pot on our lift this year but it didn’t have enough resolution. <60 ticks for 90degrees. It resulted in poor motion. We took it off and swapped it with a ctre mag encoder. The mag encoder’s quarter inch wide rod fit right in the surgical tubing we were using for the pot, so swapping from the pot was simple. The resolution went up to over 1000 ticks for the 90 degrees and all was well. Thought I’d share.

[cpapplefamily]

Yes the low resolution does seem to be the issue here.

[cpapplefamily]

Just to close this topic with the solution. CTRE released a fix for Low resolution feedback devices like a 10-turn potentiometer with FW4.22. It fixed this problem.