Our team has encountered a most unusual problem: during a match, only when plugged into a competition switch, one side of our wheel base stops working. It does not happen during all matches. As far as I can tell, it happens randomly- but ONLY when plugged into a field or competition switch. It isn't an overheating problem; our wheel base consists of four brand-new high-power motors with internal torque gearing and we have intentionally strained the robot when not plugged into a field and it had no such issue.
Our code is the standard Competition Template, and the software experts in Michigan State University's robotics program have told us they don't know of any code problem that could stop only two motors. Our lift motors have never done this.
Our wheel motors are wired through a power expander. We know there is no problem with the motors or their wires, because we had the problem at our first tournament with older motors and before our second tournament we replaced them with new ones. We think the power expander may be to blame.
Have any other teams had this problem? If so, what was the cause, and how did you fix it?