My goal was to implement the principle of the harmonic drive into a sturdy solid module that can ultimately be used for making a robotic arm. This is my first prototype, and it works quite nicely. http://youtu.be/D_neLbcW_BY The circular spline has 84 teeth. The flex spline (80 teeth) has been printed with flexible PLA. All other parts were printed with regular PLA. The bearing balls are made of copper and are 3.2 mm in diameter in size. The large bearing needs some work to get a good fit. It is currently too tight when 100% filled with bearing balls. Print settings (ultimaker) -0.1 mm @ 25-50mm/s -nozzle (0.4 mm) temp 225 degC -bed: 65 degC -0.1 mm @ 25-90mm/s depending on structure (25 for gears) Have Fun!