I really like cohlwiler's "Ellipse gear with no center pin", so I motorized it!
The parts here are used in conjunction with cohlwiler's gears and one arm. The remaining arm is either "Arm Hole Center.stl" or "Arm Hole End.stl", depending on which you desire.
Video here: https://www.youtube.com/watch?v=nD9IcBaCVA4.
Designed Sketchup Make 2015.
Printed in PLA on an Ultimaker 2 Extended using Cura default settings.
Thanks cohlwiler, excellent design!
I purchased this motor: 60RPM Speed Reducer Rectangle Shape N20# Magnetic Mini Geared Motor 6V DC (Amazon, http://www.amazon.com/gp/product/B00AUCGJX0/ref=oh_aui_detailpage_o08_s01?ie=UTF8&psc=1).
I used an old 1.5 vdc power supply directly wired to the motor.
You fail only when you decide to quit learning.