Using the Center of Percussion to Simplify a Biped to Four Point Masses

In this paper a novel strategy to construct a dynamically equivalent model of a biped robot is proposed. The model is composed by four point masses, one at the hip, one at each leg and one at the group composed by the head, arms and trunk. The masses are located at the center of percussion of each group. The method to obtain the equivalent model is described, and such a model is obtained out of a biped with parameters close to a human being. Once the equivalent model is obtained, it is validated by performing a decoupling of the dynamics of the biped and testing it using step inputs. The decoupling is done using the information provided by the equivalent model. Finally with the decoupled dynamics, the undamped natural frequency of each group (they are the both legs and the head, arms and trunk group) is calculated to confirm that each controller behaves linearly.