Unexplained intermittent CAN / 2CAN Jaguar problems at GSR

[heydowns]

v29 solved the problems we were seeing with our CAN-connected Jaguars. We no longer get random failures of the entire bus to work on robot startup as described in my earlier post.
We ran with v28 until Thursday lunch this past week and saw the boot-time failure twice during that morning.
After Thursday lunch when we put v29 on, the CAN chain (7 Jags) worked without issue for the remainder of the competition.

Originally Posted by drakesword

346 had issues at DC as well. During a couple of matches the speed of the robot would unexpectedly drop or the robot would begin shuddering (not a high speed shudder that a PID issue would show but a slow 1 second on 1 second off type issue). Finally in one of our last matches the second half of the can bus did nothing.

Sorry to hear you had problems, same for 1123 We were at DC too - wish I'd have know I would have come taken a look at your setup and try to offer some suggestions.


The CAN driver (at least for C++ maybe the others I have not looked) blocks while waiting for CAN replies to commands that are sent. If you have a Jag that is disconnected, failing, powered off, or has a poor bus connection the driver will block for a "long" time waiting for that response, thus stalling your overall code execution. This might or might not account for the slow on/off issues you describe. Of course that doesn't explain the root cause.

We've actually modified our copy of the CAN driver to shut down a device that's failing communications (repeatedly) rather than continuing to bog down the entire system in order to mitigate this.

One thing I've seen helping teams with CAN issues is that termination resistors connected in the manner described in the Jaguar documentation (that is, crimping them directly into the RJ connector on the appropriate pins) is a potential source of intermittent bus errors, particularly during match play when vibration and collisions are occurring a lot. Instead of making the cable in this fashion I recommend crimping in a short length of wire and soldering the resistor to that.
Again, not necessarily the problem your team is encountering but something worth trying/checking along with double-checking all your other bus cabling.

Also, on a very general note, as I read back on this thread it is really apparent that a number of different issues are being referenced here (symptoms may seem similar but they are caused by different things). For those just coming to this thread please keep that in mind and if you post your experiences please be as specific as possible.