The Futaba S9202 is a coreless, ball bearing, high torque servo that is designed for precise control of competition aircraft and helicopters. (This servo has also been known as the S131S and the S9201)
A note on coreless motors
A conventional servo motor has a steel core armature wrapped with wire that spins inside the magnets. In a coreless design, the armature uses a wire mesh that forms a cup that spins around the outside of the magnet. This arrangement is much lighter resulting in smoother operation and faster response time.
