servo jitter when running Jaguar on RS-775

[kamocat]

This year we used servos for our grab mechanism, and also as a latch for the deploy table. We had trouble with them moving when we didn't tell them to.
This was from two issues:

• The servos are initialized to a position when they are opened (I made a programming workaround for this)
• When moving our arm, the sevos jerk around spontaneously (the topic of this thread)

Let me give more detail.
Our arm is powered by an RS-775 on a p60 (4:1) with a jack screw. When we drive this motor, the servos jerk around. It happens more when the motor is moving than when the motor is stalled. (When I say stalled, I'm not talking about full voltage. We had some binding issues on our arm, but it wouldn't stall continuously at greater than 30% power)

I think I know where the issue is coming from - it's from the 6v power supply on the Digital Sidecar. (The other option would be the PWM buffer in the digital sidecar) Removing the DB37 and putting in a fresh battery have no effect, but removing the 6v jumper to a servo stops it, as does disconnecting power to the whole digital sidecar. (Our Jaguars are controlled over CAN)

What I don't understand is WHY this issue is happening. It's not unique to a single digital sidecar. Our 2010 DSC did this, and switching it out to a 2011 DSC made no difference.


At this point you might bring up the issue with the RS-775 shorting between its windings and its core (thus connecting to the frame). I haven't tested this on our RS-775 (having just learned about it yesterday), but I can tell you the servos and DSC are in no way connected to the frame.
I also haven't had the chance to put an oscope on the 6v and 5v power supplies on the DSC. So, until we're off of spring break, this is mostly speculation.