Thank you! I do not plan to sell these arms. I am not sure if I will be able to make time to document it (I am maintainer on an open source farming robot project which takes up most of my time - see profile), but I am working on a new actuator concept based on the principles explored in this design, and my goal with the new actuator concept is to document that and make it more general purpose, so it is easier for people to make themselves and explore this mechanical gearbox design. This should hopefully popularize this design if others like it. I think is fair to say the design is probably novel.

A fun fact about the new actuator is that it can be printed in plastic at home but is designed to be 3D printed in 316 stainless steel. I was inspired recently by the relatively low cost of 3D printing from China (I used craftcloud), and my novel actuator design relies on the fact that 3D printing allows gearbox components and robot frame members or components to be mechanically unified. This opens up new design spaces.

In this design, it is a two stage planetary with one "first stage" in between two parallel second stages. The first stage is driven by a shaft from a side mounted motor, with the shaft going through the gears in one of the second stages to reach the first stage sun gear. This parallel output better balances mechanical loads across the joint both on the input and output sides. This makes it ideal for elbow and knee style joints, and might serve to be genuinely very useful in robotics worldwide.

As with all my work it will be open source. I don't love twitter but that is currently the best spot to get updates on side projects like this. I am @tlalexander there. Alternatively, star the 3D printed robot arm repo and I will update it when my new steel servo design is done!