To set the basis here, I am helping build a 15 lb battlebot that will fight against other robots in a bullet proof area. The competition is tomorrow and the 24 hr's before hand are never very nice.
So today I go to the high school after lunch and find that the weapon motor stopped running. It turns out that there were chunks of metal inside. Now this is a hard thing to replace, as it was a Mamba Monster 2200kv brushless in runner motor, which I would rate it for 4 hp @ 13.2v. So, the kids are now desperately trying to put an 800w brushless outrunner motor in it's place. Of course it is bigger in diameter than the inrunner and the outside of it spins, so there is a lot more work to do. Also the shaft diameter was larger, so they had to go from 5mm to 6mm, which is hard b/c there are no 6mm drills. They got within .0006", but the hole was too small.
Another issue is that they were desperately over weight, so they cut 2 cells out of the 8 cell A123 pack. Unfortunately, they rewired it from a 4s2p pack to a 2s2p + 2s1p, so they could keep 14 v, which IMO was a horrible move. Fortunately, the new weapon motor is 0.3 lighter, so they might get away with 8 cells.
The original specs on this robot were two 1hp brushed dc gear motors for the drive and a 4 hp weapon that was a hoop of steel that is 5.5" dia. spinning up to 13800 rpm @ 3 lbs. I am very dissapointed that we didn't get to use the 4 hp motor, b/c the weapon would accelerate like a when you turn on a table saw! I hope to post a video of all of the fights sometime with in the next week. We used all of the best materials ( carbon fiber, titanium, brushless motors, A123 batteries ). I hope it doesn't break tomorrow
