I. Introduction
Adaptability and efficiency have always been the research focus of mobile robots. To promote adaptability, many researches have been focused on legged robots, such as quadrupedal and bipedal robots. Hutter et al. [1] developed a quadrupedal robot towards harsh environments, and [2] from Boston Dynamics presented a compact, nimble four-legged robot that can trot around office, home or outdoors. Bipedal robots [3]–[5] also showed excellent adaptability in door or outdoor. To boost efficiency, although there are a lot of researches on actuators such as [6], the most direct and effective way is to use wheels on a smooth floor. In [7]–[10] two wheeled platform were used to get higher efficiency and operating mobility. Although the robots mentioned above achieved satisfactory results in their own fields, there are increasing requirements for robots to have both adaptability and efficiency simultaneously.