Roller-Walker is a leg-wheel hybrid mobile robot using a passive wheel equipped on the tip of each leg. The passive wheel can be transformed into sole mode by rotating ankle roll joint when Roller-Walker walks on rough terrain. This paper describes adaptation of characteristics of the propulsion by a leg trajectory in the case of wheeled locomotion. Firstly, we define a leg trajectory to produce forward straight propulsion and discuss the relationships between the parameters of the leg trajectory and the characteristics of the propulsion. Secondly, we demonstrate that Roller-Walker could achieve high speed propulsion and slope climbing propulsion by changing the parameters of the leg trajectory in the hardware experiment. Thirdly, we propose an automatic leg trajectory adaptation method which is asymptotical parameter tuning method to perform specified velocity on the different surfaces with different friction. We evaluate the adaptation method in the numerical simulations. The results suggest that this adaptation method would provide the Roller-Walker with a function of an automatic transmission of a usual car.

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