Go to Post I think that FIRST should just give up and officially recognize Chiefdelphi as the place to go for community and team resources. - Greg Needel [more]
Home
Go Back   Chief Delphi > Technical > Programming
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
 
 
Thread Tools Rate Thread Display Modes
Prev Previous Post   Next Post Next
  #4   Spotlight this post!  
Unread 31-03-2016, 15:28
virtuald's Avatar
virtuald virtuald is offline
RobotPy Guy
AKA: Dustin Spicuzza
FRC #1418 (), FRC #1973, FRC #4796, FRC #6367 ()
Team Role: Mentor
 
Join Date: Dec 2008
Rookie Year: 2003
Location: Boston, MA
Posts: 1,041
virtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant futurevirtuald has a brilliant future
Re: understanding position control with encoders

Quote:
Originally Posted by Jeringo View Post
Greetings I am trying to program for a shooter that has a variable tilt from anywhere between 0 and 80 degrees. we are using a talonSRX with an encoder on it (http://www.vexrobotics.com/217-5046.html). My question is how exactly does position control work? We have set the feedback device to Quad Encoder and changed the control mode to position. From there we set the encoder counts per rev to many numbers currently 45, set the encoder position to 0. Now here is where the confusing part comes in Do I need to use SetPID and if so how do I use it. Is there a way to set the max velocity or slow the motor down? Is there any good way to calibrate the code so that I can set(10) and get 10 degrees? Thanks.
It's probably too late, but for future reference you're often better off using a potentiometer or absolute encoder for a task where you need to use a motor to move something to a specific position.

The key challenge here (which it appears you've identified) is that you need a consistent zero position in order for the encoder to work reliably (eg, if you want to say "go to X"). Often, this is a consistent starting position (where the shooter is at rest) or you can use a limit switch to identify the position more precisely. Once this is good...

Then you have to do two things. First, you need to set the P, I, D parameters (setPID). You can either call setPID, or you can set it via the web dashboard. Often, you can get by with just a P (search for forums for more about PID tuning). I usually just set P to an arbitrary number (1), and keep incrementing it until it starts moving, then I adjust the value using binary search until it gets to where the value is reliable. There are more precise ways to do this, the TalonSRX reference manual has some examples.

For limiting the speed of the arm, check out the closed loop ramp rate, which can be set via the web dashboard or via setCloseLoopRampRate.

There are a bunch of code examples that CTRE provides, I recommend checking them out: https://github.com/CrossTheRoadElec/FRC-Examples . Additionally, the TalonSRX softwware reference manual has a lot of good explanation+documentation available.
__________________
Maintainer of RobotPy - Python for FRC
Creator of pyfrc (Robot Simulator + utilities for Python) and pynetworktables/pynetworktables2js (NetworkTables for Python & Javascript)

2017 Season: Teams #1973, #4796, #6369
Team #1418 (remote mentor): Newton Quarterfinalists, 2016 Chesapeake District Champion, 2x Innovation in Control award, 2x district event winner
Team #1418: 2015 DC Regional Innovation In Control Award, #2 seed; 2014 VA Industrial Design Award; 2014 Finalists in DC & VA
Team #2423: 2012 & 2013 Boston Regional Innovation in Control Award


Resources: FIRSTWiki (relaunched!) | My Software Stuff
 


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 09:52.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi