This is an illustration of the a design principle for the 50dollar prosthetic leg program. The basic principle is to use a a rubber wedge that will create exponential resistance as the foot fends. The amount of resistance can be varied by casting different stiffness of rubber or by creating open “pockets” within the cast rubber. The design is largely based upon design input from Haakon Karlsen at MIT FabLab Lyngen.
More info on http://www2.lowcostprosthesis.org/