I was not able to calculate the exact torque needed to turn the lock cylinder but I thought a 6 kg torque servo will be enough. To test the servo, I needed a way to attach the servo to the door and I started to think about the enclosure. At first, I thought I may use a 3D printer to build the enclosure but it was not going to be cheap, because I don't have an 3D printer.

Enclosure Material

I found these cylindrical cardboard boxes. They have used to be the boxes of t-shirts that i bought. With 800mm of diameter, it is the perfect material to work on.

Servo Holder

Cardboard boxes has removable caps so I did cut an rectangle and screwed the servo using its mount points. I can use existing screws to attach another cap to the door.

I removed the knob from the lock cylinder and used the hole on the cylinder to attach a longer pin. This long metal pin will be used to attach the servo arm to the lock cylinder.