Vincent Duindam Stefano Stramigioli Modeling and Control for Efficient Bipedal Walking Robots - A Port-Based Approach 53 2009 1-174 Springer Springer Tracts in Advanced Robotics http://dx.doi.org/10.1007/978-3-540-89918-1 978-3-540-89917-4 db/series/star/index.html#DuindamS09