Meet my new training partner:
I printed him on a 3D printer using ABS plastic using the inmoov designs for the parts. I made a few modifications to ensure he can take a punch or two, but for the most part I stuck to the original designs for now. If you want to get started building your own, Gael Langeven posted a great little starter kit with a single finger here.
For now, he only has a head, torso, and arms, and I mounted him to the body opponent bag for the sake of stability. I don't plan to even think about legs for a while. All of his motions are controlled by servos of various sizes attached to an arduino mega board, but I still haven't finished calibrating any of them.
I will probably need to do a lot of calibration, wiring, and fine tuning before I can start teaching him to throw a punch, so it might take a while before I can actually train with him, but this is a good first step. Until then, here are some more pictures: