To get around this, [RoTechnic] moved the wrist stepper motors off the arms entirely. He built a push-pull mechanism that uses braided fishing line to transfer motion to the robot arm’s wrist ...
According to this article on the project [Kachi Chan] used Cinema 4D to simulate the motion, ROS for control, PincherX150 robotic arms modified with Dynamixel XM 430 & XL430 servo motors ...