Go to Post Gotta love the use of universal technical terms, along with whatchamacallit, doodlespiel, whosiwhatsit... ;) - PaW [more]
Home
Go Back   Chief Delphi > Technical > Electrical
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rate Thread Display Modes
  #16   Spotlight this post!  
Unread 11-01-2009, 22:29
writchie writchie is offline
Engineering Mentor
AKA: Wally Ritchie
FRC #2152 (Team Daytona)
Team Role: Coach
 
Join Date: Dec 2007
Rookie Year: 2007
Location: Daytona Beach, Florida
Posts: 148
writchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond repute
Re: Current Measurement

Quote:
Originally Posted by DeepWater View Post
I'm not sure why we would ever need more than 50A. We can't have any motor on a breaker greater than 40A so why wouldn't 50A be enough. Same with the 20A and 30A Phidgets on 20A or 30A breakers. Please explain further if I am missing something.
Motor currents can approach the stall current for short periods of time. You can have loads of 60 amps for 2 second and 100 amps for hundreds of ms without exceeding the capabilities of the battery, breakers, or speed controllers.

If you limit yourself to breaker amperage, your measurements will be clamped at 50 amps during these periods. This may or not matter to your application.

In this years game, friction may limit the maximum torques and consequent motor current for drives. But you could still have higher currents in your mechanism, especially shooters.

Also keep in mind that the speed controllers are PWM. Your current is pulsed (around 100hz for victors, 15kHz for jaquars). You need to integrate the current over time to have an meaningful values.
  #17   Spotlight this post!  
Unread 11-01-2009, 23:00
ChuckDickerson's Avatar
ChuckDickerson ChuckDickerson is offline
Mentor / Bayou & CMP Division LRI
FRC #0456 (Siege Robotics)
Team Role: Mentor
 
Join Date: May 2004
Rookie Year: 2004
Location: Vicksburg, MS
Posts: 877
ChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond reputeChuckDickerson has a reputation beyond repute
Re: Current Measurement

Thanks, I wasn't really thinking about spikes. Where did you find that they are good for 500% over their measrement range?

We are interested in current measurement mostly for use in traction control so I am guessing large spike due to stalled drive motors may not be a huge problem this year. I am assuming that a jammed or locked mechanism driven by a CIM would stall the motor long enough for the breaker to kick out but I could see that brief large spikes would occur when say a CIM shifts from full forward to full reverse. Any thoughts as to if these Phidgets would smoke on a brief spike like this or just max their reading?
  #18   Spotlight this post!  
Unread 12-01-2009, 00:07
writchie writchie is offline
Engineering Mentor
AKA: Wally Ritchie
FRC #2152 (Team Daytona)
Team Role: Coach
 
Join Date: Dec 2007
Rookie Year: 2007
Location: Daytona Beach, Florida
Posts: 148
writchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond reputewritchie has a reputation beyond repute
Re: Current Measurement

Quote:
Originally Posted by DeepWater View Post
Thanks, I wasn't really thinking about spikes. Where did you find that they are good for 500% over their measrement range?

We are interested in current measurement mostly for use in traction control so I am guessing large spike due to stalled drive motors may not be a huge problem this year. I am assuming that a jammed or locked mechanism driven by a CIM would stall the motor long enough for the breaker to kick out but I could see that brief large spikes would occur when say a CIM shifts from full forward to full reverse. Any thoughts as to if these Phidgets would smoke on a brief spike like this or just max their reading?
See the datasheet for the allegro sensors. 500% will protect them from damage. The way these work is that the sense terminals go through the IC package so that the magnetic current in the wire is sensed by hall effect inside the package. There are electically isolated. I think they can withstand 500% overload indefinitely.
  #19   Spotlight this post!  
Unread 12-01-2009, 08:47
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: Current Measurement

This will add to your confusion...
All motors are in stall when power is applied and the rotor is not moving...i.e. when starting.
Snap action breakers can withstand a 600% over current without trip for a second or two, 200% overload for up to 10 seconds.
Snap action breakers reset almost immediately.
CIM motor is 129 amps at stall,
Battery is capable of delivering 600+ amps at full charge.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.
Closed Thread


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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Cheap Torque Measurement? ChuckDickerson Motors 15 13-06-2005 13:57
measurement problems? jakk General Forum 2 16-01-2005 17:22
Drill motor gear measurement dmellich Motors 10 23-06-2004 12:03
Current Sensor Adam Shapiro Electrical 48 11-02-2004 07:06
Actual execution time measurement Dan Technical Discussion 5 24-03-2003 11:36


All times are GMT -5. The time now is 19:39.

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