[Al Skierkiewicz]

ak,
I went back and read over your post again. Am I correct that you have one controller feeding all four motors? Is that one controller output or two motors on one output and two on the other output? The motor controller is intended to power only one Tetrix motor per output. The controller has over current sense and will shut down if the current is too high or the temperature climbs above a certain point. If the controller is shutting down for a fault, it may fail to pass I2C signals on to the following devices. The specification sheet lists the current output for each motor circuit at 4 amps which is below the stall current for the motors.