For Professor Asada’s 2.120 Robotics course Fall 2013 we took on the challenge of wearable robots. The problem statement was to develop an exoskeleton that could actuate a set of human legs, thus providing mobility for wheelchair bound persons. Our approach was a 4 bar linkage mechanism, controlled by 4 Dynamixel Absolute Servo Motors. Super pricey hardware (~500$ each), especially considering the remaining budget was $200, but great torque in a little package.
The linkage was composed of milled HDPE, shoulder screws, thrust bearings, and 4 – 4lb RC car shocks. The two hip motors were direct drive mounted at the center of the upper link. The two ‘thigh’ mounted motors drove a belt attached to shin link. An advantage to the 4 bar is the ability to calculate EVERY angle (10 total) in the system by comparing each of the 4 encoder readings in real time.