The door electric motor is a very simple device. The electric motor turns series of spur gears that serve as a gear reduction. The last gear drives a rack and pinion gear set that is connected to the actuator rod. The rack converts the rotational motion of the motor into the linear motion needed to move the lock.
The motor spins the gear, the clutch swings out and locks the small metal gear to the larger plastic gear, allowing the motor to drive the door latch. If the door latch is moved, all the gears will turn except for the plastic gear with the clutch on it.