“what kind of servomotor?” I mean, which specifications (torque, maximal speed, reversibility…)
Cool if you are doing energy based walking. I am on the same way (At this moment, I mix a bit a lot of approach and see what happens on the real robot).
My nightmare for the moment is "SENSORS 
" . I should have spent more time on sensors at the beginning of the project. For instance, if you want an estimation of kinetic energy, you must have a good gyroscopic sensor and a good estimation of the height of the center of mass…