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CAN Jaguar Speed or Current Control with Current Limit or Thermal Cutoff
Three possible solutions are posted... the solution to use depends on the primary problem one is trying to solve:
a) Prevent the wheels from slipping by limiting torque? Try the Jaguar in speed control mode with cRIO limiting current.
b) Prevent the Jaguar's current shutoff from tripping or limit current for traction control? Try the Jaguar in current-control mode with cRIO controlling speed.
c) Protect the motor from overheating? Try the Jaguar in speed-control mode with cRIO limiting time-averaged square of the current.
Each solution has its potential benefits and flaws:
a) If the traction current limit is too high, this approach will not protect the motor from overheating. A current limit low enough to prevent motor overheating will not allow short-term higher motor currents which may be desired.
b) Speed control may be less effective. Provides no motor protection or traction control if current limit is set too high.
c) Requires a bit of testing to gather empirical data to properly tune the low-pass filter. There may be some scenarios where the filtered value does not track the motor temperature adequately. Does not provide traction control.
Attached Files
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CAN Jaguar speed control with current limit (Rev C)
current_limit.pdf
download file
uploaded: 08-18-2010 10:37 AM
filetype: pdf
filesize: 2.69kb
downloads: 448
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CAN Jaguar speed control with thermal cutoff
thermal cutoff.pdf
download file
uploaded: 08-18-2010 02:56 PM
filetype: pdf
filesize: 3.12kb
downloads: 311
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cRIO controlling speed and limiting current with Jag current control
current limit 2.pdf
download file
uploaded: 08-19-2010 12:28 AM
filetype: pdf
filesize: 3.58kb
downloads: 332
Discussion
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08-18-2010 01:07 AM
RyanCahoon
Re: paper: CAN Jaguar Speed Control with Current Limit
It seems to me that there wouldn't be enough bandwidth between the cRIO and the jaguars to implement this effectively, as I believe [kamocat]'s testing says roundtrip communication times are in the 10s or 100s of milliseconds, and current spikes will potentially be shorter than that.
While it may help against motors sitting in stall for long periods of time, I'm not certain if this will retain all the desired points of current control mode. Could definitely be worth testing, however.
--Ryan
08-21-2010 11:58 AM
Ether
Re: paper: CAN Jaguar Speed Control with Current Limit
Thanks for your comments Ryan.
If the concern is the circuit breaker in the Jag, take a look at the Jag in current-control mode with cRIO controlling speed.
If the concern is motor damage due to overheating, the thermal cutoff approach might provide some protection.
If the concern is traction control, using the Jag in speed-control mode and providing a current limit in the cRIO might be the best thing to try.
~
08-22-2010 12:59 AM
RyanCahoon
Re: paper: CAN Jaguar Speed Control with Current Limit
I guess my comments were mostly because I hadn't seen the usage cases.
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