[electroken]

Based on your description, it sounds like your frame is actually connected to battery negative. The polarity is irrelevant though.

Some RS-775 motors have been known to get internal shorts to the housing. In some cases these connections are intermittent and orientation dependent. I haven't seen this with any of the RS-550 motors with my own eyes, but the designs of the two motors are very similar.

While this condition will cause your robot to fail inspection, I doubt it is the reason for your communication problem. I would check for metallic debris in the Digital Sidecar and perhaps try another ribbon cable. Our Digital Sidecar can attract metal chips from distant planets.

Of course code is a possible culprit, but I'm a hardware guy so...