A leg-wheel robot has mechanically separated four legs and two wheels, and it performs high mobility and stability on rough terrains. The adaptive gait for large rough terrains of the leg-wheel robot is composed of three gait strategies. In this paper, the step-down gait, which is one part of the adaptive gait, is described. The point of the flow of the step-down gait is described. When the robot approaches a downward step, a forefoot touches the surface deeply. It forecasts the existence of the downward step by the information on the forefoot's touch point. After that, the robot does the step edge searching operation. This searching operation is the point for going down the step, since the robot fell under the step if it has walked without knowing the step. When the body goes down the step a little, the load sharing ratio of legs increases so that the load of the body rests upon legs. Therefore, the robot finds the edge of it, and it changes footsteps for preparation of going down the step. After the preparation, it can lower the body from the step supported by all legs and wheels. To lower the body, the following items are needed similar to the case of an upward step: 1. Acquisition of target value of lowering the body. 2. Correspondence to difference between target depth and actual depth.
This paper is the full translation from the transactions of JSME Vol.72, No.721.
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