Runaway CIM motors

[MrForbes]

We use Victors to run the drivetrain motors, they seem to be less likely to fail in strange ways than the Jaguars. We've never had a Victor fail on a robot, but we've had a couple Jaguars fail the one year we used them for the drive motors.

Stories like this confirm that we're probably doing the right thing....even though many teams use Jags and don't have any problems...

[JamesCH95]

Originally Posted by squirrel

We use Victors to run the drivetrain motors, they seem to be less likely to fail in strange ways than the Jaguars. We've never had a Victor fail on a robot, but we've had a couple Jaguars fail the one year we used them for the drive motors.

Stories like this confirm that we're probably doing the right thing....even though many teams use Jags and don't have any problems...

I will second this, with the caveat that the black jaguars seem to be way better than the brown Jags. I don't think I've had a black Jaguar die yet *knock on wood*

[BullBot Mentor]

We will try to order another Victor and go with that. I am going to check the alignment of our drive wheels and chain to make sure we are not overloading the motor.

Thanks again.

[StevenB]

Just to second what's been said already: if you've pulled out the PWM cable, and the motor is still running, the problem is the speed controller. It can't be the code, it can't be the encoders*, it can't be the computer, it can't be the joystick, or anything else. If there isn't any signal going into the Jaguar, and it's still running, it's broken.

I don't know what your replacement plan is, but you probably don't want to run one side of your drivetrain with a Victor and one side with a Jaguar. They have slightly different input/output curves, so the motors will run at different speeds given the same input. It certainly won't break anything, but it will probably be harder to make your robot drive straight.

* If you're using CAN, there is a way to run the Jaguars with direct encoder feedback, which will allow the Jaguar to drive the motor without being sent a constant command. Even so, it still shouldn't run on startup.

[BullBot Mentor]

Thank you for your input,

We did order another Victor and plan to switch our drive motors to the Vics and our arm motor with the Jag. Without a "true root cause", we loosened the drive chains slightly to relieve some load on the motor. We had averything running OK yesterday, except for 1 side down without a controller. Our student morale picked up with the successes we did see and a game plan to get our new friend rolling.

Now, if we can just keep the jags from smoking...

[slijin]

Immediately check your robot for a chassis short.

Although Jaguars are a point of failure, applying 12V across drive motors will spin them, no matter where the source. Albeit unlikely, make sure that this is not the case.

[Al Skierkiewicz]

Did a limit switch jumper on the Jaguar fall out? It is possible that the Jag is trying to get back from a limit condition. Full on is not the general failure on these devices. It happens but it is vary rare. If the PWM cable is left inserted and you disable the robot, does the motor continue to spin?

[BullBot Mentor]

I did take the Jaguar apart to inspect for damage and did not see any. I did not check to see if there was a misplaced jumper. Thank you for the advice.

We did disable the robot with the PWM cable removed and when enabled again, the motor took off.

[Al Skierkiewicz]

If you could check the jumpers, reinstall the PWM cable and let us know what happens when you power the robot, when you enable and then what you see on the Jaguar during each condition. With the PWM installed, does the motor spin immediately when power on the robot?

[StevenB]

Originally Posted by Al Skierkiewicz

Did a limit switch jumper on the Jaguar fall out? It is possible that the Jag is trying to get back from a limit condition.

I've never used a Jaguar with limit switches, but I'm confused how this could happen. The switches are supposed to be wired normally-closed, so if a jumper came out the Jaguar would act as if the switch had been pressed. The Jaguar datasheet specifically says that the motor stops when a switch is pressed. Am I missing something?

Originally Posted by Jaguar datasheet

Two limit switch inputs provide a method for immediate shut-down of the motor. The inputs expect typically-closed contacts - one for each direction of rotation.
http://www.ti.com/litv/pdf/spmu064c

[Al Skierkiewicz]

Steven,
If limit switches are not used, there must be jumpers in place on the Jag.

[BullBot Mentor]

Originally Posted by slijin

Immediately check your robot for a chassis short.

Although Jaguars are a point of failure, applying 12V across drive motors will spin them, no matter where the source. Albeit unlikely, make sure that this is not the case.

Thank you for the tip. We did stop and check all connections to make sure we were not shorting anywhere and everything looked good. We will check again when we meet up this evening.