This is a locking 12 step ratchet and pawl mechanism I designed for a project I am working on. http://youtu.be/l4CXz2UywVQPrinted in ABS on an Ultimaker 2 at 230C with a 0.2 mm layer height. The ratchet is advanced using a standard servo with approximately a 30 degree throw. I used an arduino to control the servo in the video. The pawl is screwed inline 26.57 mm from the center of the ratchet. The center of the servo hub is positioned 25.5 mm out and 38.3 mm up from the center of the ratchet. The ratchet arm is connected to the servo on a 19 mm arm. All of the holes are 2 mm but can be drilled larger.