I have a torque 2818/900 motor on a aerobatic plane and a castle thunderbird esc, The motor is not turning easily as it should so I took it off the plane to see if anything was wrong with it. When I unplugged it from the esc it spun easily and when I plugged it back into the esc it was tight turning again. There is no battery hooked up just sitting on the bench , Does anyone know what causes this? and how to fix. Thanks, Mark