My way of balancing rc motors. Using tape, iPhone, and iSeismomotor app. It is a slow process, but for multicopter platforms quite useful process. Start with marking the motor with Sharpie marker, run the motor, check the vibes. put a piece of blenderm or any other clear tape, and run the motor again. Check the vibes. If no change move the tape 1/8 to the left or right from the marked dot. Check the vibes again. If there is no change, move the tape again 1/8 in the same direction as previous time. At some point there will be a small improvement in the vibes. That is the spot where you should start adding more tape, check the vibes, and keep adding tapes until you see the vibes starting to build up again. That means that you have put too much tape at that point and over balanced the motor. Pull out the last piece you add, and that's it. Your motor should be balanced.
