56mm Banebot problems @ Championship

[cire]

We didnt see any noticeable problems with them, but to be safe we decided to take them off our robot and replace the carrier plates after our last practice round on thursday. This was the worst decisision ever! It took us 3 hours to take off the gearboxs, they keys and sprockets had gotten stuck on the shafts and we ended up having to make a little tool to press them out. When we did get them off there was no visible damage at all inside the gearboxs (we were running only 1 CIM). We replaced the plates anyways and put them back on the robot. We were there until 8pm on thursday and spent the first 2 hours of Friday putting it back together. When we got it all running again the right side kept binding up and it made it real hard for our driver to go straight and turn at all. So we took it off again during a 2-3 hour break between matchs, this time we didnt remove the shaft from the drivetrain but just the motor and most of the gearbox. I went arround and asked about 15 teams for a gearbox until I found one that had a spare (most teams had already given them away to other teams). We ended up not using it because the inside of the gearbox worked fine after we cleaned it out, so i gave it back on Saturday (Thanks 1732!).

What a nightmare.

[billbo911]

I know this may not be the best thread to post this in, but the information is quite appropriate for this thread.
During the Davis regional, we burned up two CIMs and damaged two 56mm trannies. Ultimately we figured out the root cause and made a modification to our bot to stop the problem from re-occurring a third time.
During build season, we determined that adding the outboard drive shaft support bearing would be a really good idea. After receiving the bearings, we fabricated to mounts and put them on our bot. We didn't notice until the second time we replaced a motor and tranny that when the support bracket was assembled to the bot that it didn't actually support the end of the shaft (long story that doesn't need to be spelled out here). Needless to say, the student who installed it the first time said, "oh, I was going to fix that later, but forgot." That aside, without the support, the output shaft was being pulled off axis.
Inside the trannies, the output shaft has a short extension that protrudes into the center of the final sun gear. The clearance of this fit are quite small. Once the shaft is pulled off axis, the little extension rubs against the inside of the sun gear. No amount of lubrication is sufficient to dissipate the friction this causes. The resulting heat and binding caused the sun gear to seize onto the output shaft. As you might imagine, really bad things happen when the final stage of a planetary gear system becomes fused together.

So, how do you fix this problem?

Bore out the sun gear to allow plenty of clearance. Make sure the end of the output shaft is properly supported!!!

Once these two steps were completed, we had no further problems with our drive train.

BTW, this happened with a hardened carrier plate as well as with the original plate.