My attempts at creating the foot drives are definitely a challenge. I'm not sure if it will work but my current prototype seems like it has some promise. But I will have to get some heavier gauge aluminum. As you can see from the pictures, it's close to the one picture I have of the drive I'm modeling my R2 from. As far as I know there's only one person who has made their R2 this way. Maybe some of the builders coming over this weekend will be able to shed some light on this project.
Next I have to cut the feet slots on top out and then cut the inner piece where the battery box is located. It has to be cut out for the motors to fit. Also this drive is directly connected to the leg so the ankle has very little stress on it as opposed to the other 99.9% of R2's out there.
I hope I can get this design to work because these motors are sweet.
These pictures are of my prototype