Howstuffworks “How Power Door Locks Work”
The stepper motor / gears option is very noisy. I am considering ditching the variable lock and going for something like this car door lock. The part (from Jaycar) is 10AUD and very nearly thin enough to fit within the door cavity.
The mechanism should have heaps of torque – that would mean I could replace the spring on the deadbolt returning the authentic noise. I think its a simple motor with gearing – when i supply 12V it shoots out and stops – the motor still tries to run but the sound isn’t bad.