This paper discusses the mechanical kinematics solutions and design aspects of the biped robot SHERPA, a bipedal platform able to walk and carry load. Starting from the analysis of the human lower limbs, we figure out that 6 DOF per leg are fundamental for a correct walking motion and can be adopted in a mechanical design of a humanoid robot. A close investigation of the joints leads us to a novel modular mechanical design, with a parallel architecture mechanism characterized by and high degree of interchangeable components. The robot is using twelve high performance hollow shaft electrical actuators acting in pairs in a parallel manner, a remote compact and transparent actuation with zero-backlash cable transmissions, 2 DOF differential joints between each segment of the limb and a light-weight carbon fiber skeleton modeling and mimic the anatomy of the human legs. The modular 2 DOF cable differential joint has been successfully implemented at the hip, knee and ankle level. Using our approach, actuation is more transparent (backdrivable, with low inertia) and will allows SHERPA to interact with the environment more smoothly which leads to better walking ability.