First of all the engines look very good, smooth as a baby's bottom. It looks solid from the outside, but after my newbuild crashed, I heard a rattling noise in one of the motors. I'm assuming it's camp, but I feel like it shouldn't be normal after an accident. Oh, before this accident, these were some of the most amazing and stable engines I've tried, but I haven't had a chance to try them again. Flies well, durability is questionable.