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Unread 09-13-2017, 06:55 PM
dardeshna's Avatar
dardeshna dardeshna is offline
AKA: Devin Ardeshna
FRC #0008 (Paly Robotics | Team 8)
Team Role: Mechanical
Join Date: Dec 2015
Rookie Year: 2015
Location: Palo Alto
Posts: 164
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Tuning a PIDF follower on a robot with high gearing

One of the problems we have been encountering during the off-season is tuning a PIDF follower reliably on our 2017 robot. It is geared with a fairly high theoretical top speed (~17fps), and our autonomous trajectories are generated with a maximum velocity of about 5fps. This means there isn't much torque at the wheels compared to resistive forces.

Without feedback terms, velocity does not track well. Generally a kV and kA value that work at faster speeds (4-6fps) are inadequate for slower speeds (2-3fps). We can add in feedback, but a few things happen:

1) The Kp term does more corrective work than it should be doing
2) Because of the large error, following is inconsistent between different trajectories

How do teams overcome this inconsistency at lower torque and get better tracking with feed-forward terms before moving on to adding feedback terms?
Devin Ardeshna
Alumnus (Paly Robotics FRC #8)

2018 (FRC #8 - Team Captain) Arizona North Regional Quarterfinalist and Entrepreneurship Award, Silicon Valley Regional Semifinalist
2017 (FRC #8 - Build Captain) Ventura Regional Quarterfinalist, Entrepreneurship Award, and Creativity Award, Silicon Valley Regional Finalist, Entrepreneurship Award, and Wildcard, Roebling Division Semifinalist, Chezy Champs Quarterfinalist, Capital City Classic Semifinalist
2016 (FRC #8 - Safety Captain) Central Valley Regional Finalist and Wildcard, Silicon Valley Regional Quarterfinalist, Curie Division, CalGames Quarterfinalist and Entrepreneurship Award, Capital City Classic Quarterfinalist
2015 (FRC #8 - Student) Central Valley Regional Entrepreneurship Award, Silicon Valley Regional Entrepreneurship Award, Capital City Classic Semifinalist and Judges' Award
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