The present invention is a compound planetary gear system which has a moveable sun gear and a lockable sun gear to change the gear ratio between a high gear ratio and a pseudo 1:1 slipping ratio. The system makes use of a ratchet and pawl mechanism to provide a safety backup for when the lockable sun gear is locked. The invention may be used to move the aircraft from a stationary position, for taxiing, and for pre-rotating the wheels prior to landing.