Speed controllers going out of sync randomly

[Briansmithtown]

We need help asap for a very important presentation, and our robot is acting funky. It drives randomly. We asked Mark McLoed, and took his advice and it worked for a while, but it is acting up again. Please help

[NWChen]

What was Mark's advice? Can you describe the issue in more detail (LED status indicators on speed controllers, what do you mean by "funky"/"randomly," have you made any code changes)?

[Petzer]

Originally Posted by NWChen

Can you describe the issue in more detail (LED status indicators on speed controllers, what do you mean by "funky"/"randomly," have you made any code changes)?

Although I can't speak for exactly what Mark said as I wasn't present, as we turn on our robot from the breaker our Victor 888 speed controllers randomly give power to any motor controlled with a Victor 888. I do believe he said that it could be one speed controller causing the whole problem, but we haven't had time to test it yet. While disabled (meaning teleop and autonomous were not running), the LEDs mainly were completely off for the short spurts the motors moved. While in teleop, this behavior seemed to occur a bit more frequently except the other indication colors on the LEDs appeared. Again, this occurred without any code telling it to do so, as we once removed a PWM wire from one and the motor still continued as such. As Brian implied, the robot was acting normally before a couple days ago when it started acting like this.
Hope this helps, if you need more info please feel free to contact me.

[Jon Stratis]

I would start by removing all PWM's to the Victors - does the problem still happen with all motors? Or does that limit it to just some? If it limits the problem, replace the affected victor(s) and give it another try.

If it still happens with all the victors... try looking for a short somewhere. Check the power going into the victor and make sure you see appropriate +12V - it's possible you have a short that's feeding in reverse polarity (maybe attached to a motor, so it only shorts when the motor is in a specific position), which would cause funky issues and probably wreck the victors.

Try pulling the breakers to all but 1 motor controller - can you get that controller to behave properly? If so, add breakers back one at a time until things go funky - that'll tell you which power pathway/victor/motor is causing the issue.

If unplugging the PWM's fixes the problem for all victors, I would replace the digital side car and try again. It's possible there's some metal shavings in there that are giving an intermittent contact on the PWM control wires, or one of the chips may have gone bad/burned out to cause funky behavior.

When dealing with odd situations like this that appear to be system-wide, it's usually best to break the system down to its simplest form and then start adding features/parts back on - that way you can start from a position you know is working and find the area that is actually causing the problem.

[Tem1514 Mentor]

I had a similar problem and found two problems.
One was a shorted motor and the other was the pins on a PWM cable that were shorting inside the Victor from being pressed in to hard.

[MrRoboSteve]

Consider swapping the digital sidecar. Random PWM signals is a failure mode of that part.

[Petzer]

Originally Posted by MrRoboSteve

Consider swapping the digital sidecar. Random PWM signals is a failure mode of that part.

After looking over the digital sidecar quickly today, we discovered that it was the culprit. When we have the time, we'll be swapping it out with a good one. Thanks for the input!