Drive Motors turning off then losing signal
 

Hey all,

Before the competition is announced, we wanted to show our new members how the basics of the FIRST robot operates, and also to refresh our knowledge of how everything works. So we rebuilt a small little chasis with a simple 4 motor drive. We have 2 CIM Motors fitted into Andy Mark CIMple box which drives a chain to the wheels.

So anyway, the problem is whenever we engage teleop, the Jaguars connected to the motors will flash red, the motors will turn for half a second, then the motors lose signal and blink yellow.

We've really been trying everything we could possibly think of. We've reformatted the cRIO, we've remade the program several times over, we've checked all the wiring. Still can't figure it out.

I'm really sorry about the pictures of the code being, err, actual pictures instead of a screenshot, but I was being kicked out of our room so I had to take them quickly :( We're coding in Labview.

Alright, so this is the picture of the teleop code. It is extremely basic, as we've JUST been trying to get this to work.


This is the begin code. We basically opened a 4 motor drive, watchdog, and a joystick. That's it.


If there are any questions about the code I can answer them.

Right before I went home today, we found that if we just plugged in one motors PWM cable, that one motor would work. But only in 2 directions, foreward and left. If the joystick was moved to the right, or down, the Jag would flash red and the signal would be cut.

Any help would be greatly appreciated! It's really been bothering us for about a week and a half now. Thanks!

Re: Drive Motors turning off then losing signal
 

From our teams experience using jaguars is that they can sometimes fail and cause intermittent problems like the ones you describe. Also, make sure that you're motors aren't running in opposite directions and that your gearbox is working well. I don't usually use labview, but I thought that it was unnecessary to use a watchdog and that could be causing the problem. You might want to try running them motors without them connected to the gearbox. If that doesn't work, I'd just try creating a new robot project and not adding the watchdog. Also, double check that all your parts are well connected, and that the joystick is on the same port in the driver station ans in LabView.

Re: Drive Motors turning off then losing signal
 

There is absolutely no reason to reimage the cRIO in this circumstance. It is a complete waste of time. And I didn't look too closely at your code, but I doubt that is the issue.

1. Verify that your battery is charged. As the motors draw current, the voltage of the battery drops. If it drops too low, the motor controllers may stop working.
2. Verify that the motors are not fighting one another and that they are not drawing too much current because of binding or because of the gear ratio.

Greg McKaskle

Re: Drive Motors turning off then losing signal
 

Check your digital sidecar wiring, it was a source of problems for us.

Re: Drive Motors turning off then losing signal
 

Ah, yes.

I meant to include that one. Specifically, verify that you have supplied power to the digital breakout itself. The PWM signal supplies just enough power for a few motors to function when no power is connected to the breakout, but it isn't predictable and needs its own power in order to operate correctly.

Greg McKaskle

Re: Drive Motors turning off then losing signal
 

Thanks for the answers!

I don't think it is the motors moving against each other, because they WILL spin, but they lose signal. Hard to explain but we definantly made sure they were not moving against each other.

The gearbox is fine because again, they do work, but it's only in one direction. I'm thinking it is an electrical issue.

As per reformatting the cRIO, we didn't really know what to do so that was one of our last options. And we've rewrote the code several times with and without the watchdog.

What exactly do you mean by supply power to the digital breakout? This sounds like it could be the problem. Is this a module on the cRIO or is it on the digital sidecar itself. Noob question, I know :(. It's been a while.

Thanks for the answers though!

Re: Drive Motors turning off then losing signal
 

It'd be the sidecar itself. Down at the bottom (Where PWM port 1 is) there should be a Wago connector that carries 12v from the Power Distribution Board.

Re: Drive Motors turning off then losing signal
 

I'm almost postive we have that plugged in. It might not be the right voltage though, I'll check on monday.

Re: Drive Motors turning off then losing signal
 

Grab a spare Jag from somewhere, power it, and plug in a PWM. If it functions properly, you've got 2 bad jags. We had the same problem not long ago, and thought we were going crazy because we replaced a bad jag with another bad jag.

3rd times the charm.

You can easily check if the motors are fighting each other by disconnecting one of the PWMs and running the other.

Re: Drive Motors turning off then losing signal
 

The symptoms point perfectly to the Digital Sidecar not receiving battery power. Make sure you've got its power input wired to a 20-amp circuit on the Power Distribution Board.

Re: Drive Motors turning off then losing signal
 

Yeah, sorry for not coming back and answering! It turns out we did not have the power coming from the right source! Found a handy wiring guide that I cannot believe we did not have before.

Thanks guys! :D