Abstract
In this paper, we study on the influence of state transition of touch ground on biped robot walking. We have been developed a small humanoid robot "Dynamo" for the RoboCup. "Dynamo" can walk stable and fast relatively. However, robot sometimes fall over. It is caused by changing the state of sole of the foot. We consider the reason of the fall is change of motion period of the center of the gravity. Then, we constructed a model that considers the feet, ran a simulation and actual verification. We also observed how change of angle of ankle affect walking. We consider the impact on the walking ground state from these data.