Martijn Wisse Daan G. E. Hobbelen Arend L. Schwab Adding an Upper Body to Passive Dynamic Walking Robots by Means of a Bisecting Hip Mechanism. 112-123 2007 23 IEEE Transactions on Robotics 1 http://dx.doi.org/10.1109/TRO.2006.886843 db/journals/trob/trob23.html#WisseHS07