A mechanical engineering student from the University of Michigan designed and 3D printed a Motorized Star Wars AT-AT model. The AT-AT, including the gears and motor parts that make it walk, is entirely 3D printable with the exception of the small 90 rpm motor and 9V battery clip. It was designed in Solidworks and includes 69 individual parts. The gears were actually designed to intentionally give the AT-AT the same herky jerky movements from the movie. You can read more about this project over on 3DPrint.com: http://3dprint.com/112943/3d-printed-walking-at-at/