Go to Post I can't claim to be an expert in the stess analysis field - I just play one on TV, er CD, er - okay, so call me a poser! - petek [more]
Home
Go Back   Chief Delphi > Technical > Programming > Java
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Reply
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 15-05-2012, 12:37
MorocoMan MorocoMan is offline
Registered User
FRC #2212
 
Join Date: Mar 2012
Location: Isreal
Posts: 9
MorocoMan is an unknown quantity at this point
jaguars - send voltage

hello.
I know that if you replace the PWM by CAN then you can send a constant voltage from the jaguar instade of a percente of the voltage of the battary.
my question is there is another way to do it? and what are the up sides and the down sides of CAN againts PWM?
Reply With Quote
  #2   Spotlight this post!  
Unread 15-05-2012, 12:56
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
Posts: 10,798
Al Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond repute
Re: jaguars - send voltage

Mo,
The Jag doesn't send a constant voltage, it can be commanded to operate in "Voltage Mode" through the CAN bus. In this mode the Jag produces an "average voltage" that simulates a constant voltage so that the motor behaves as if it always is receiving the commanded voltage. In this mode you can also program a "ramp" which will change the average voltage over a specified length of time. I know there are several teams that have used this mode that can comment on it's usefulness.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.
Reply With Quote
  #3   Spotlight this post!  
Unread 15-05-2012, 13:36
FrankJ's Avatar
FrankJ FrankJ is online now
Robot Mentor
FRC #2974 (WALT)
Team Role: Mentor
 
Join Date: Feb 2011
Rookie Year: 2009
Location: Marietta GA
Posts: 1,942
FrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond reputeFrankJ has a reputation beyond repute
Re: jaguars - send voltage

I know referring to the output of the jag as a DC voltage is not technically correct, but lets go with it in the interest of simplicity. The jag documentation refers to voltage output as well.

The PWM & default canbus mode (%VBus) converts the command from -100% to 100% output. The actual voltage out depends on the command signal & battery charge.

One of the CanBus modes is called Voltage. Its input is a voltage & it measures the incoming battery voltage & adjusts the actual command to try to give a constant output voltage independent of the battery charge. Sort of a poor mans close loop control.

We used it on our shooter this year & it seemed to help.

The only to access this mode is through can. Can gives you more controls & simplifies wiring. It is a single point failure that will bring down everything connected with. There are some programming gottyas that stop the whole robot. Done right it can be very reliable.
Reply With Quote
  #4   Spotlight this post!  
Unread 15-05-2012, 14:13
EricVanWyk EricVanWyk is offline
Registered User
no team
 
Join Date: Jan 2007
Rookie Year: 2000
Location: Boston
Posts: 1,597
EricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond reputeEricVanWyk has a reputation beyond repute
Send a message via AIM to EricVanWyk
Re: jaguars - send voltage

You can try to recreate your own Voltage Mode control over PWM. Set your PWM output to (Desired Voltage) / (Measured Battery Voltage) each cycle. The advantage of CAN in this setup is that it measures the voltage more often and more accurately (closer to where it is used).


As Al said, it doesn't actually create that voltage - it just does a good enough approximation of it. For FRC purposes it should be indistinguishable.

The advantage of voltage mode control in general is that it reduces the impact of your battery voltage and current draw on the behavior of the motors. In Percentage control, the voltage / oomph applied to the motor can easily change by +/-40% as conditions change.
Reply With Quote
Reply


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 12:54.

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