View Single Post
  #7   Spotlight this post!  
Unread 27-10-2014, 12:08
Joe Johnson's Avatar Unsung FIRST Hero
Joe Johnson Joe Johnson is offline
Engineer at Medrobotics
AKA: Dr. Joe
FRC #0088 (TJ2)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1996
Location: Raynham, MA
Posts: 2,644
Joe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond repute
Re: Jaguars and FAST PID Looptimes

Quote:
Originally Posted by AustinSchuh View Post
20 ms is the old Victor update rate. You can hit 5 ms (might need to tweak the WPILib constants, can't remember, but the hardware can do it) with the Talon SR. That gives you 12 cycles to settle, which might be enough.

How did you come up with 90 degrees in 60 ms?
I've had mixed results with deducing the update times with WPILib. I am going to have 4 loops running at all times this isn't a burst mode. I remember some very odd behavior showing up in other, unrelated bits of the code. I think it was something related to the threading that WPILib was doing in the background.

Kinda creeped me out frankly.

I know that the Jaguar comes with it's own baggage but at least it lets me find out if an updated loop time allows for sufficient control. I may try a half measure where for this project (not FIRST legal obviously) where I put a coprocessor between the CRio and a Talon that is doing the PID loop itself. Kind of a Kludge but answers the question of "can a Talon SRX do this?"

As to the oddly specific spec of 90 degrees in 60ms, it falls out of a calculation for path following at the various speeds of interest. But in actual fact, it is somewhat arbitrary (faster is better could have been the spec), but part of the point if a Fall Practice Project is to discover the edges of what is possible. The easiest thing in the world is to slow the steering rate down. And I may have to go there, but i am not starting there.

Joe J.
__________________
Joseph M. Johnson, Ph.D., P.E.
Mentor
Team #88, TJ2

Last edited by Joe Johnson : 27-10-2014 at 14:06.