Aaron D. Ames Ryan W. Sinnet Eric D. B. Wendel Three-Dimensional Kneed Bipedal Walking: A Hybrid Geometric Approach. 16-30 2009 HSCC http://dx.doi.org/10.1007/978-3-642-00602-9_2 conf/hybrid/2009 db/conf/hybrid/hscc2009.html#AmesSW09