Designed by BirdBrain Technologies and Rich Juchniewicz for the Solarbotics GM8 motor included in the Hummingbird Robotics Kit. Will fit the D-shaft on any GM2/3/8/9 motor. Make sure to print it flat side down.
If you print at home, you may need to drill out the two Lego peg holes as the tolerance on most printers is not sufficient for the pegs to fit snugly. We used the following drill bit: http://www.mcmaster.com/#30565a269/=r1seea
Works well with a Lego forty tooth gear or a Lego pulley (see pictures).