I have had the same problem. After several total tear downs and rebuilds, checking, gears, retaining collars, bearings, brushes, etc. It still would not get more than 6" off of the ground. I decided to try a battery balance check. There is a simple,cheap unit on the market called a "Blinky" it plugs into the 3 pin on your battery. It works by dicharging the stronger cell thus rebalanceing the battery. After rebalanceing, recharge and then balance again. You may need to do this several times at first. You should be able to find these at your local RC, or on line. if you have trouble finding them go to colpar hobbies web site in Denver Co. I have found that not only is it flying great but it has increased my flite time. Hope this helps!!