Kazuyuki Hyodo Sadayoshi Mikami Sho'ji Suzuki Stabilizing passive dynamic walk by constraining leg angles by foot shape. 2083-2088 2008 ICARCV http://dx.doi.org/10.1109/ICARCV.2008.4795852 conf/icarcv/2008 db/conf/icarcv/icarcv2008.html#HyodoMS08