Did you get a chance to really inspect the seized gearbox to see exactly what was binding? There was a thread earlier in the season about the second stage sun gear binding up and that had a lot of good tips for avoiding this:
http://www.chiefdelphi.com/forums/sh...ad.php?t=53427
Generally, avoid side loads (support the other side of the output shafts), lubricate well, check for full engagement of the output shaft with the plate (sometimes the little spacer rings are missing and the shaft only goes part way into the final stage), and break them in before running at load. (Current draw should drop after a few minutes of running freely to 2.5A or less per motor.) Also, I think several teams have cut the shaft that the sun gear rides on completely and just let it float.
After we installed new carriers, one of our transmissions went back together no problem and ran smoothly. The other would be tight at particular angles. The less-than-technical solution was to see which side the planet gears were tight on and try to "persuade" the output shaft in the opposite direction by resting it on a hard surface and tapping with a hammer. Better to prevent the situation altogether than to have to resort to this, though. Good luck!
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MIT Mechanical Engineering
>> College Mentor,
Team 97: Cambridge Rindge and Latin School with The Edgerton Center, MIT Mechanical Engineering, Bluefin Robotics, and Draper Laboratory
>> Alumnus, Team 527: Plainedge HS