URGENT(ish): Twitchy motors
 

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?

Re: URGENT(ish): Twitchy motors
 

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

Re: URGENT(ish): Twitchy motors
 

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.

Re: URGENT(ish): Twitchy motors
 

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. :)

Re: URGENT(ish): Twitchy motors
 

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.

Re: URGENT(ish): Twitchy motors
 

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

Re: URGENT(ish): Twitchy motors
 

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?

Re: URGENT(ish): Twitchy motors
 

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.

Re: URGENT(ish): Twitchy motors
 

We have seen the same behavior on rebooting the cRio.

Re: URGENT(ish): Twitchy motors
 

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.

Re: URGENT(ish): Twitchy motors
 

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.

Re: URGENT(ish): Twitchy motors
 

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.

Re: URGENT(ish): Twitchy motors
 

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/sh...ad.php?t=73640
http://www.chiefdelphi.com/forums/sh...ad.php?t=75067

Re: URGENT(ish): Twitchy motors
 

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

Re: URGENT(ish): Twitchy motors
 

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