We had a similar problem this year. During driver practice we would be able to run the robot for about 3-4 minutes. After that the cRIO would randomly reboot or we would pop the 120 amp main fuse. We checked if the frame was grounded or if any metal shavings were found in the PD board and found nothing. This problem continued multiple times afterwards but we still haven't diagnosed the problem because the next day was bag and tag day.
However after searching chief delphi for answers we found this:
http://www.chiefdelphi.com/forums/sh...ad.php?t=91733
We use a Banebots 775 to tilt our shooter. It is directly mounted to our aluminum frame. Since the motor only shorts out as different spots. This can explains why you don't see any electrical problems when we test for conductivity to the frame. We currently think that this may be our problem.
If you use a Banebot I would disconnect power to it and see if you experience the same problem.