OCCRA
Go to Post NASA rarely launches another rocket just so the programmers can see if they've fixed a bug. - Greg McKaskle [more]
Home
Go Back   Chief Delphi > ChiefDelphi.com Website > Extra Discussion
CD-Events   CD-Media   CD-Spy   FRC-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
  #21   Spotlight this post!  
Unread 04-17-2012, 06:26 PM
billbo911's Avatar
billbo911 billbo911 is offline
Registered User
AKA: That's "Mr. Bill"
FRC #2073 (EagleForce)
Team Role: Mentor
 
Join Date: Mar 2005
Rookie Year: 2005
Location: Elk Grove, Ca.
Posts: 1,847
billbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond reputebillbo911 has a reputation beyond repute
Re: paper: Shooter Wheel Speed Control

Quote:
Originally Posted by Ether View Post
I should have been clearer:

The "low_command" is a tuning constant, not the target speed, and was not intended to be so low that it tops out at a speed below the "spinup_speed". "low_command" should be high enough that it briskly accelerates up to (and beyond) spinup_speed, at which point the full voltage is applied.

Many shooter wheel setups can handle application of full voltage to the motor even at zero RPM, but some can't. It's a function of the gear ratio and the wheel inertia and the motor being used. For such setups, simply set spinup_speed=0.0

The code I posted was for those shooter setups that can't handle a full 12 volts being applied at zero RPM, but could, for example, handle, say, 8 volts at zero RPM and 12 volts at 1000 RPM. For that example, you would set spinup_speed to 1000 RPM and low_command to 8 volts. Simple, and gets the job done.

With the code I posted, the minimum continuous RPM is simply commanded as the target speed by each team's software to whatever they want it to be, and the code I posted will bang-bang regulate at that speed. That target speed can be zero if the team so desires.


For really finicky setups (e.g. high inertia wheel, not much gear ratio), you could always add a third "else" statement:

Code:
if (measured_speed >= target_speed) motor_command = 0.0;

else if (measured_speed >= spinup_speed) motor_command = 1.0;

else if (measured_speed >= medium_speed) motor_command = medium_command;

else motor_command = low_command;



Got it. So, in essence, you want the absolute maximum acceleration possible, for the particular shooter design, that it can handle without tripping the over-current.

With the version I added today, you can set the trip point for low to high acceleration as well as the rate of slew rate limiter. By tuning these two, you can achieve almost exactly what you are describing. The only difference is the start up voltage will be a ramp, with an adjustable slope, instead of a step from 0v. Granted, it is not the absolute fastest acceleration you can get, but I doubt the differences will be noticeable in actual performance. You will see it on a scope, but that's pretty much it. I'm guessing a only few millisecond difference between the two designs from 0 RPM to target RPM in the 2500-4000 range.
__________________
So long and thanks for all the fish!

CalGames 2009 Semi Finalist, CalGames 2009 Autonomous Champion Award winner
Sacramento 2010 Creativity in Design winner, Sacramento 2010 Quarter finalist, 2010 Madtown Creative Design Award
2011 Sacramento Finalist, 2011 Madtown Engineering Inspiration Award
2012 Sacramento Semi-Finals, 2012 Sacramento Innovation in Control Award, 2012 SVR Judges Award.
2012 CalGames Autonomous Challenge Award winner ($$$).
2013 Pow3rhou53 Pwnage Gracious Professionalism Award.
2014 2X Rockwell Automation: Innovation in Control Award (CVR and SAC). Curie Division, Gracious Professionalism Award.
Reply With Quote
 


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 07:51 PM.

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


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi