Actually I’m literally designing a new motor and constructing it from scratch, and is a high torque brushless motor design that requires my custom controller, which will also be open sourced. The motor has sufficient torque that I hope a 1:10 gear reduction will be enough to drive a biped leg, and this low gear reduction allows for the use of (large, wide tooth) printed gears. The driver is current controlled and uses torque-vector control for moving the rotor, so integrated hall effect position sensors (analog) are used to accurately sense rotor position to a few degrees.
The new motor with high torque and low gear reduction means it safely backdrives, and the cost of the system is reduced by not needing an expensive gear train. It is largely theoretical at this point but I have extensive manufacturing experience and have built a handful of brushless linear motors in the past using this controller so I’m not totally dreaming here. The first prototype motor works in static torque tests but the coils were a little undersized to I have just sent files for quote on a new stator design. The previous stator was 3D printed stainless steel but for the next version I am looking at waterjet cut steel sheet that I will stack. This will have better magnetics properties and will likely be cheaper. Ultimately I will want to have these manufactured in china though with the construction method I use it is pretty cheap to make in the US. The rotor is printed plastic.
I am doing a lot of research into 3D printed mechanisms and hope to help designers reduce the cost of their robotics through the concepts I am developing (which will all be open sourced). For example here are some slightly out of date pictures of the 3D printed remote control car I am building which already works extremely well. With chinese tires (not shown) it has enough grip (and power) to do standing wheelies on asphalt/tarmac!
I suppose I should upload some pictures of my current motor design as well…
Anyway, the complete “servo” design is going to be almost entirely 3D printed aside from some skate bearings, and the motor consists of a printed or laser/waterjet cut stator with hand-wound coils. Basically everything else will be printable on a home printer. Unfortunately I have a “real job” which interferes with my ability to design robots, but it’s a self-run business so I try to split time when I can.