This Robotics Stack Exchange discussion seems pretty good: https://robotics.stackexchange.com/questions/10616/why-is-it-so-hard-to-walk https://robotics.stacke

This Robotics Stack Exchange discussion seems pretty good: https://robotics.stackexchange.com/questions/10616/why-is-it-so-hard-to-walk https://robotics.stackexchange.com/questions/10616/why-is-it... This one, less so: https://robotics.stackexchange.com/questions/8129/why-are-bipedal-robots-difficult https://robotics.stackexchange.com/questions/8129/why-are-bi...