So this is more a story about how I decided to build this robot and why. Before the CM6 robotic arm, I made Faze4 robotic arm. 

Faze4 is a massive 6 axis 3d printed robotic arm that weighed 15 kg. It uses 3d printed cycloidal gearboxes and stepper motors. It was designed to look nice and clean (let's not kid ourselves CM6 is crude and all over the place) but Faze4 was too massive and stiff for what I had planned to do with robotic arms. I could have closed the stepper loop with encoders but I still had problem of using heavy and inefficient steppers and not to mention high gear ratio cycloidals that are hard to backdrive. I wanted to build robotic arm like BLUE from UC Berkeley. 

BLUE used high torque density BLDC motors, custom-made drivers, and belts to get more torque. That combination gave it quasi-direct drives, making the robotic arm compliant, able to change its stiffness, and interact safely with the environment. 

Another project that inspired me was that of Ben Katz, where he used legs of his mini cheetah to create 2 arms that performed bilateral teleoperation.