CIM motors vibrate/jitter

We have a mock up chassis for testing code on. It has the bare essentials, including 2 talons and 2 mini-CIMs. When we power up the setup and run code, everything works fine, however the 2 CIMs vibrate/jitter. We have tried different CIMs, different sizes, different Talons, they still jitter. We’ve tried everything we can think of an they still jitter. Any help would be great, thanks.

So the robot “twitches” on the ground, as in it drives very slightly back and forth without user input telling it to do that?

Is the robot enabled when this happens (so does it happen when the robot is disabled as well)?

We don’t have any wheels hooked up to it, as it is just on a C-channel frame. When we enable it, the lights on the Talons flicker between red and orange. When it is disabled, they don’t jitter.

It’s (most likely) a code issue. Red means the Talon is getting a reverse signal, while orange means the Talon is getting a neutral signal. If it’s bouncing between the two, it’s most likely caused by a code issue, but you can try calibrating the Talons as well.

Although possible, I don’t believe so. We’ve sent it code that had no other commands other then to set the motors to 0. It still bounces back and forth several times a second between the two colors.

Are you routing your PWM wires parallel with all of your power wires to the motors? The induced current could mess with the signal, but if you’re not running them I doubt this would occur. Just controls food for thought.

That being said, do calibrate them. If the calibration is such that a zero signal is right on the line in the talon of neutral/reverse, it would probably bounce between them as you said.

Well, we have the PWM wires tied next to eachother most of the way until they split, and one place that could be a problem is I looped them up at one point to shorten them up, just a simple back and around loop, but could that be the issue?

It is very possible that something is telling the Talons to go full throttle and in doing so they trip the breaker feeding each one. Do you have any wiring attached to the output of the Talons? Double check this to be sure you don’t have a short there.

Something is causing the mixed signal and thus the jitter. Check your DSC connections.

Yes, we have wiring. They are not making contact though, it’s circle screw on connectors connected to wire running straight to the CIMs, no metal contact.

Having the PWMs next to each other wouldn’t be an issue, just big current flow through the power wires from the PDB. - Pg 7 is the calibration instructions.

All of the DSC connections are proper. We disconnected them all and reconnected them.

Are these Talon SRs? If so, then red/orange flashing is the fault code for under voltage (<3.3V), over temperature (>170C), or shorted output transistor.

Yes, I believe they are the Talon SR motor controllers. This doesn’t seem like an error code, as it is flashing extremely fast, as in 15+ times per second, and the motors are actually moving. They are hooked up identical to our robot, so they shouldn’t be under volted. They have fans on top of them, and the flashing is all they do, so it can’t be over heating. I also doubt that it is a shorted out transistor, seeing as we have tried different talons. It must be something to do with the DSC or CRio, however we have no clue what. We’ve reconnected everything, but nothing seems to work.

Have you tried calibrating them as suggested by dellagd above? It sounds like they are getting a signal right on the edge of neutral and based on timing jitter it is alternating between neutral and a very low speed reverse.

It’s probably a race condition in your software. Can you post your code?

The LED indication you describe is the Talon responding to a command that takes it in and out of the 4% of deadband condition. Something is commanding the Talons to do that. The Flashing orange is the indication that your are close to the deadband condition and the flashing red is an indication that a throttle command has been sent to the Talon. The LED flashes Red or
Green in proportion to the throttle command sent to the controller.

Good day,

I am wondering if any success has been seen on this issue. Our robot is seeing a similar issue with running the CIMs. With a configuration of the driver station without the Xbox controller that runs our drive train, the motors will behave in our Auto-tests. But, after being left on for a duration of time, one, and sometimes two, of our CIMs begins to jitter, and the robot becomes non-static.

If the Xbox controller is plugged in, the error still occurs, and any usage of the controller does not clear the twitch condition.

After a power reset, it seems to work okay, but then it comes back.

I’m suspecting digital cables too close to power lines and is getting a induction that the software can’t clear out.

thanks for any input,
WPI in three days !!!

Jim Boivin
Mentor, FRC Team 811, FLL Referee/Judge/Coach

Your first step should be to calibrate the motor controllers, as was suggested above, this issue (if you’ve ruled out code and joystick calibration as sources) is likely due to a PWM signal that is slipping out of the deadband.

Other possible sources are bad ribbon cables from the DSC (with this I believe you would see jitter even while driving) and battery voltage/reset conditions.