Remixed from http://www.thingiverse.com/thing:51489 (user 271828 - thanks!) This modified spindle has the string hole removed for strength, and is extended down to just above the base, with a tapered hole for motor cog. I used an old Honeybee CP2 helicopter brushed motor, which surprisingly has plenty enough torque to launch the blades 30+ meters. This would be lethal with a more suitable motor that is designed for direct drive as in this application (low Kv/rpm , more torque). Motor was attached by adding some screws to it's in-built mounting holes but not screwing them up, then heating the motor with a heat gun and melting it into the end of the handle. The screws melt the plastic and slide up into the slot on the bottom of the handle for a solid mounting. The cog melts into the tapered hole of the spindle.