Okay, i’ve got a puzzler for you guys. We recently went to competition, and, for the 4th time this year had issues with motor burnout in our drive train. Sounds pretty normal, but the thing is that we recently re-geared our drive train to work with 6 motors, and were burning out maybe 45 seconds into every match, but could drive for a half-hour uninhibited before running into issues. I’ve looked everywhere and can’t find any solutions that aren’t “make sure you have a backup battery” or "make sure your batteries are properly secured.
As of right now, my current hypotheses are:
a) the drive train motors are in a power expander, and somehow VEXNet is messing with that
b) the Cortex is taking some issue with VEXNet operating it and is causing the internal capacitors in the motors to freak out
That’s all I can come up with, and I’m dying here, so please tell me if you know of any solutions!
Internal motor PTCs take ~30 mins to fully cool. It is very possible that, while running your robot, the motors gradually heated up, and, after not having enough time to cool between matches, finally tripped. It could also be the cortex/power expander PTC. If you have too many motors on one of these, the current draw will trip the entire section. Make sure to distribute your motors between different ‘breakers.’ Cortex ports 1-5 and 6-10 are on two seperate PTCs, and the power expander is on another. It is generally a good practice to split up your subsystems between them. For instance, on our (6 motor) chassis, we have the front left and front right motors in the power expander, back left (2) motors in cortex port 2, and back right (2) motors in cortex port 6. It is important to have no more than 4 motors on each PTC; while 4 motors CAN trip one if they are all under load, it is generally safe. Note that two motors on a y-cable still count as two motors. As a general rule, put two power expander ports on cortex PTC 1, and the other two on cortex breaker 2. Most y-cables should be on the cortex, as there are now only two available ports per PTC (the other two are taken by the expander).
lt;dr:
Motors cool down slowly, so the heat doesn’t reset between matches. Your motor distribution could also be at fault, make sure to split up your motors between cortex/expander PTCs.