i just encountered the same problem with mine.. my main gear was missing some teeth and thought it was that... i was wrong.. turned out to be the esc... my baldes would spin up real good and then they would slowy stop.. tried everything... then i swaped out the esc with one of my other birds and sure enough it was the esc..

its only had a few flights on it but my last crash a main blade stuck in the ground.. i think the baldes strike is what stripped my gear and caused the esc to short out because of the sudden stop on the blades???? jake