I wanted to design a part that would allow a common hobby servo to unlock a deadbolt. You could then use RFID or some other means of authentication to open a door.

I used the larger size available at Radio Shack.

To start, I designed this mount in OpenSCAD, to be bolted or double side taped to a door, over the deadbolt:

Then I needed a cup to fit over the deadbolt handle. I designed the included screw to fit to secure the arm on the servo, but I ended up not using it.

On the other side, I used OpenSCAD code from Charles Rincheval for the servo spindle teeth, the code of which is available at https://github.com/hugokernel/OpenSCAD_ServoArms. Despite each tooth on the servo being only 0.5 mm in length, the Prusa i3 printer I used was able to print the spindle teeth to be more than strong enough for this purpose. The torque that you can get from them is more than the servo can generate itself.

Here is a test fit of the cup I made. It took two tries but it fits snugly.

Here is the servo mounted to the base, the inset screw heads fit great.

Here is the device, assembled and mounted, in the open position.

Here it is, in the closed position.

The OpenSCAD files used in this project are available at https://github.com/rhinoceraptor/arduino-deadbolt-opener.