A motorized bicycle derailleur assembly has a motor unit, a movable part (e.g., a motor linkage, a derailleur linkage and/or a chain guide) and a controller. The movable part is in response to activation of the motor unit within a mechanical stroke. The motor unit has a motor output stroke with a prescribed maximum movement range that is larger than the mechanical stroke of the movable part. The movable part has an anti-jamming arrangement having an anti-jamming spring. The anti-jamming spring is configured and arranged to compress when the motor unit continues to apply a moving force to the movable part after the movable part reaches a lockup position. The controller is configured to set the motor unit output stroke to an operating movement range that is smaller than the prescribed maximum movement range so that the anti-jamming biasing element remains uncompressed during normal shifting operation.