I wanted a servo/robot actuator to use with a medium sized quadruped (cheetah) and a small humanoid robot. Hobby servos were too slow, low torque, had poor control, high backlash or were too expensive. The idea then began to create low cost actuators with enough torque/speed and were fully under my control that would suit my robot design requirements.

I actually started with magnetic transmissions. Their designs intrigued me. It was why I purchased my cheap Chinese 3D printer. It allowed me to easily create rectangular slots for Neodymium Magnets. I will create a project on the following in the future.

• Cycloidal Gearbox
• Balanced Cycloidal Gearbox
• Dual Magnetic Wobbling Gears with Constant Velocity Joint
• High ratio Planetary Gearbox

Ultimately magnetic transmissions could not deliver enough torque. They had a strange property of having zero backlash at zero torque and increasing the backlash as the torque increase, at high torque the gear would just slip. 

I then looked at 3D printed gearboxes after seeing the work by "Gear Down For What". I trialed some single, dual and differential Planetary gearboxes. The Single stage ones were ok, but practically the gear reduction ratio could only be about 5:1 and would not produce enough torque. I would have to use a dual stage reduction gearbox and that would not be nice.

Then the design of the Mechanical Cycloidal transmission started.