URGENT(ish): Twitchy motors

[csshih]

our motors sometimes twitch around even though the pwm values are zeroed.
all of our firmware and software(Labview) is up to date
does anyone know whats wrong/ have similar issues?

[Al Skierkiewicz]

Craig,
Are you using Jaguars or Victors? I have noted some twitching with the Jaguars we are testing.

[nathanww]

Probably too late now--but this could be a calibration problem. You should look up the calibration procedure for whatever speed controller you're using and recalibrate them.

[Alan Anderson]

our motors sometimes twitch around even though the pwm values are zeroed.

A noisy PWM signal to the speed controller might do this, but there's no obvious way for that to happen. Unless maybe your Digital Sidecar doesn't have a good 12V power feed, and it's stealing current from the Digital I/O module's output? It's always worth checking to make sure the power cord is plugged in and providing power. :)

[wilsonmw04]

We noticed that our robot will do the same thing from time to time. We traced the problem back to a loose power connection on the power distribution board. When you lose power for a moment, the robot will continue to do the last command it received for a short period of time. For us, it would go into a short loop (~ .25 seconds) and twitch.

[csshih]

we're using victor for the launcher.. which is what's twitching, but we had a jag twitch too, but it stopped.

[Jared Russell]

My money is on a calibration issue.

Can you print out the PWM command to verify that it isn't something wonky in the program?

[ay2b]

I've seen all of our motors (on Jaguars) twitch slightly upon rebooting the cRio from the DS. It doesn't happen all the time. This seems consistent with other comments indicating a twitch upon loss of a signal.

[Jon236]

We have seen the same behavior on rebooting the cRio.

[Jared Russell]

On rebooting the cRIO, sure, we've seen twitching as well. However I don't *think* that this is the issue the thread starter was talking about.

[VEI Dude]

I haven't really touched any of the controls at this point, but I do remember reading something about the PWM being the same as a servo PWM signal. If so, you should be able to isolate the problem with a servo or a servo tester (to generater servo signals).

Also, I saw on ours that some of the ring terminals were placed under the metal pad (not on top, between the pad and screw), so the connection was not secure. I thought it could be a flaky signal, so perhaps check for that just in case.

Cheers,
-Neil.

[csshih]

Sorry guys, I am unable to provide more information,
as our robot is now in the realm of Fedex.

The twitching does not only come up with the boot of the cRIO, it continues as long as control is activated. when the system is booted up, it is fine.

also, strangely enough, the twitching seems to be systematic.

thank you guys for your help.

[Don Wright]

Are you using an analog sensor to provide feedback to a control loop controlling this motor? There is an issue with faulty code giving false analog signals which could be causing your PID to make the motors twitch...

http://forums.usfirst.org/showthread.php?t=12020
http://decibel.ni.com/content/thread/2325?tstart=0
http://www.chiefdelphi.com/forums/showthread.php?t=73640
http://www.chiefdelphi.com/forums/showthread.php?t=75067

[Garii]

Actually, I had a problem with this, we were using a feedback node though an and gate that allowed us to turn on our motors and keep them on until the button was pressed again.

for some reason it was the boolean feedback node, I removed it and everything work fine except everyone was annoyed when I told them they had to hold the button instead of pressing it =p

[eugenebrooks]

There is an update of WPIlib that is reputed to resolve
the problem with the analog inputs. It also updates a
lot of other things...

http://first.wpi.edu/FRC/frcupdates.html

[Liu_yiang]

Our robot didn't have a problem with twitching as much as it did with a constant speed, even though our readouts read zero. Our fix, strangely enough, was to copy and paste each individual part into a new program, with the exact same name. This also got rid of a nasty delay within our program.

[Peragore]

While this is thread necro, we are getting a twitch problem whenever our robot is enabled. For some reason, we are not getting this twitch on the robotic arm. The robot motor will still twitch even when we have the motor in action. while there is no joystick input, we also get the twitch problem. Note that we have a working deadzone on the joysticks.

[Alan Anderson]

While this is thread necro, we are getting a twitch problem whenever our robot is enabled. For some reason, we are not getting this twitch on the robotic arm. The robot motor will still twitch even when we have the motor in action. while there is no joystick input, we also get the twitch problem. Note that we have a working deadzone on the joysticks.

Are you using Jaguars or Victors? Did you tell the software which one? What kind of drivebase do you have (how many motors, how many wheels, how is the motor power transmitted to the wheels, etc.)?

[Peragore]

We are using jaguars, but we did manage to fix it. There was a conflict between Tank drive and our motors. The tank drive class and the jaguar class were both sending signals (0) that are not synced up, therefore creating a signal slightly off zero, causing our motors to twitch. Thanks anyways

[Kevin Wang]

If the motor is controlled by a joystick input, then it may help to make sure that the joystick zeroes properly. This program helps in testing joystick axes and buttons:

http://www.softpedia.com/get/System/System-Miscellaneous/Joystick-Tester.shtml

[frc2590]

Kendrick: try to change the throttle trim or also AKA calibration