Quote:
Originally Posted by johnmaguire2013
I don't understand motors, electricity, etc. however I have a question on behalf of my team, and I think I'm wording this correctly.
Basically, we used CAN with Jaguars for our robot's drivetrain this year. Multiple times it stopped working during the match, and our team was seemingly able to determine that this was due to built-in protection on the Jaguar to stop, essentially, surges. It was happening when a large amount of voltage was sent through the Jaguar I believe, and our team said this wouldn't be an issue if we switched back to PWMs. It would usually happen if our driver was moving back and forth very quickly (e.g. the bridge.) Does anyone have an idea of what was happening or how this could be fixed?
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I think our mentor, Steve Phillips, puts this situation in the best perspective...
Imaging you're in your car, driving down the freeway, at 70MPH. Then you decide you simply want to go into the opposite direction. You change from drive to reverse, and hit the gas. What's going to happen? Well, I'll tell you what isn't going to happen... you won't be going the direction you want to be going. What will happen is that you'll likely break a lot of stuff in your car.
Same concept applies here to robotics. You have a 120lb robot going at 15FPS. That's quite a bit of momentum built up. Your driver suddenly wants to go the other direction, and slams it into the other direction. First off, the motors are creating back EMF of about 12V, and plenty of current capability, you then tell the speed controller to apply -12V, and give it all the current it can. You have a difference of 24V now, right? Given that you're technically going over the stall current because of the back EMF, you're probably putting a load of 200+ Amps on the Jaguar. It simply cuts out for protection. The Victors don't have this protection built in. They'll try to back drive, and the only overcurrent protection they have are the 40A snap action breakers. If you didn't have those in the circuit, they would literally self destruct, and actually, I know we have had a few in the past self destruct because of the conditions you described.
The ramp mode will keep you from reaching the cut-out condition, but you'll lose some maneuverability. The best solution is to make sure the drivers remember this concept, or switch to Victors and use PWMs.