Fastest Elevator Controllable Speed

FIRST General Forum
1

2011 had very fast elevators with the top level teams sporting elevators capable of getting from the floor to the top peg in under a second. With the improvements in frc control since then (I.E. Talons), we should be able to go even faster right? My team is trying to figure out how fast is too fast for a light weight elevator. What is the fastest possible elevator speed that could still be controlled with the current control system(talons)?

2

I don’t know what the answer is. But here are what we’re considering for the speed:

  • Momentum. Be sure to get a video if you go too fast with too much weight. I’m sure it will be hilarious.
  • How much the elevator will move in between Talon read cycles. It’s configurable; I haven’t looked at the updated Talon software to know what the new methods are called. The default was 100ms for our settings last year, which explained our inconsistency with distance in auton last year.
  • Whether the periodic read performed by the Talon is faster than what the sensor can produce (i.e. you get the same readings multiple times in a row).
3

Generally speaking, the electrical part of an electromechanical system reacts much faster (> 10x) than the mechanical parts, so it is unlikely that the new controllers will bump the practical limits on elevator speed. An old-school Victor 888 can accept pwm input at 4ms/250Hz and drives the output at 1kHz, which means you can get ~50 setpoints in during a 1s lift, assuming you have CPU cycles on the RIO, which is 2500x higher at 667MHz.

That said, 2011 had a lot more motor restrictions than this year. There’s probably a more practical difference here.

4

You should be using Motion Magic, Motion Profiling, or PID control onboard the Talon for this. The onboard PID on the Talon happens at its update rate of 1ms. Motion magic will let you set a target position, cruise velocity, and acceleration, and then it will magically generate and follow motion profile obeying those parameters. Basically it calculates what position it should be at every 1ms and then servos to it. At which point you set a reasonable velocity and acceleration and then start cranking them up until something screams.

5

2.638 meters per second.

:rolleyes: