[Russ Beavis]

It doesn't sound as if you've run the "up on blocks" test that I recommended - lift the robot off the ground and electrically spin the wheels. In this configuration, you should read zero acceleration (with the exception of gravity and any vibrations that couple the motors to the accelerometer).

Reading -5G is obviously an indication that something is broken. You'll need to either fix that problem (broken PWM cable?) or replace it before doing anything else.

Russ