[Al Skierkiewicz]

Capacitors are legal for noise suppression only. You could not find a big enough capacitor to hang on a motor to help if brownout is the issue. And then it would only work if your motor was just spinning in one direction. Large caps usually are not bipolar. It is possible that you are tripping the breakers feeding the motors or that the controllers are faulting. A common issue for long runs is to use too small a wire gauge. There can be considerable voltage dropped across smaller guage wire.