View Single Post
  #7   Spotlight this post!  
Unread 09-14-2017, 03:41 PM
Oblarg Oblarg is offline
Registered User
AKA: Eli Barnett
FRC #0449 (The Blair Robot Project)
Team Role: Mentor
 
Join Date: Mar 2009
Rookie Year: 2008
Location: Philadelphia, PA
Posts: 1,601
Oblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond reputeOblarg has a reputation beyond repute
Re: Tuning a PIDF follower on a robot with high gearing

Quote:
Originally Posted by GeeTwo View Post
The biggest reason is the carpet. Almost any surface pair will have a larger coefficient of static friction than of dynamic friction due to developing bonds between the two surfaces. In the case of carpet, it deforms relatively slowly and rebounds inelastically, so the net friction rises as speeds decrease. I suspect that carpet fibers also work their way into any crevices in the wheels over time, furthering this effect.
Well, our current plan is to attempt to better-account for the effect of friction by, rather than computing Kv from a single data point (measured max speed), run the robot at a variety of voltages, measure steady-state speed at each, and perform a linear regression. The reciprocal of the slope will become Kv, and the negation of the intercept will become a constant "friction compensation term" that we will add to all of our velocity setpoints. This should, in theory, accurately account for any frictional effect that is itself linear with velocity (and a glance at the residuals from the regression should give us some insight into the degree to which it is nonlinear).

We will document how well this works, and probably write a short whitepaper on it. Hopefully, it will go some ways towards allowing us to have a single Ka gain work reasonably well over a wider range of accelerations.
__________________
"Mmmmm, chain grease and aluminum shavings..."
"The breakfast of champions!"

Member, FRC Team 449: 2007-2010
Drive Mechanics Lead, FRC Team 449: 2009-2010
Alumnus/Technical Mentor, FRC Team 449: 2010-Present
Lead Technical Mentor, FRC Team 4464: 2012-2015
Technical Mentor, FRC Team 5830: 2015-2016

Last edited by Oblarg : 09-14-2017 at 03:46 PM.
Reply With Quote