Thread: CAN Jaguar losing power temporarily
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Unread 04-02-2012, 14:50
slibert slibert is offline
Software Mentor
AKA: Scott Libert
FRC #2465 (Kauaibots)
Team Role: Mentor
  
Join Date: Oct 2011
Rookie Year: 2005
Location: Kauai, Hawaii
Posts: 343
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Re: CAN Jaguar losing power temporarily
I don't consider myself an expert, but here's what we learned and what we decided to do:

- We found that our CAN-based Jaguars (we use Speed mode and PercentVBus mode) pull over 40+A (which doesn't seem to trip the PDB breaker because it happens so fast there's not time for the thermal switch to overheat) when we drive full speed (4 CIM motors, mecanum drive) one direction and then switch to full reverse. This causes a Jaguar "brown-out" b/c the voltage drops below ~6V. Polling the Jaguar to determine if it rebooted since the last time we asked is our proof of this.
- We *tried* detecting the reboot (which works) and if so re-programming the Jaguars back into speed mode (which doesn't work, may be a bug in our code). We couldn't get it to work, not sure why yet but we had to move on (and we came up w/a solution that works for us, see below).
- We found the Jaguars reboot pretty quick, and when they do they default to PercentVBus mode. The drivers don't seem to notice when they reboot when the Jaguars are in PercentVBus mode.
- The drivers really like the full power and quick response they get being able to drive the robot "full tilt", so we decided *against* the recommended approach of having a "ramp" in software to soften the rate of change. Your mileage may vary on that decision...
- We also tried the "automatic ramp" in the later Jaguar firmware. It didn't seem to help us avoid the problem, I'm also not sure (documentation unclear) if it works only in PercentVBus mode or not (i.e, I'm not sure it actually takes effect in speed mode). We decide to leave this feature enabled (via the rotated jumpers on the Jaguar), thinking that it probably helps things - but it doesn't eliminate all "brown outs".

We decided based on all of this to use Speed Mode in Autonomous, PercentVbus Mode in Teleop, and we are working on an "end-game" (bridge-mode) where we transition back into Speed mode and have a virtual "low gear" mode which makes it easier to control the robot when on the bridge. When in speed mode, we avoid high-amp situations.

At this point, our solution is working pretty well. Our drivers are not complaining anymore about the drive system!

Hope that helps,

- scott (Kauaibots, team 2465)
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