# Design, Analysis, and Experiment of a Wheel-Legged Mobile Robot  
[PERSON]  
Key Lab for Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin 300350, China  
Correspondence: [EMAIL_ADDRESS] (Z.Z.); [EMAIL_ADDRESS] (T.S.)  
[PERSON]  
Key Lab for Mechanism Theory and Equipment Design of Ministry of Education, Tianjin University, Tianjin 300350, China  
classified into four types: tandem type, separate type, transformable type, and hybrid type. The tandem wheel-legged robot [24; 25; 26; 27] moves on flat ground with wheels and changes its posture using the leg structure when encountering obstacles. It has good mobility. A wheel-legged robot with a variable attitude robot mechanism was designed in [39], enabling the robot to conduct various configurations and omnidirectional motion. However, only its wheels come into contact with the ground, which results in slightly poor obstacle-crossing capability. The separate wheel-legged robot [28; 29] switches walking modes according to different terrains. In the case of flat terrain, its wheels come into contact with the ground; in the case of steep terrain, its legs come into contact with the ground. It improves obstacle-crossing capability, but switching between the two modes causes complexity in control. The transformable wheel-legged robot [1; 30] adapts to different environments by switching the wheel-leg state. The wheel-leg structure has a built-in motor, which allows for switching to the wheel or leg shape mode according to the terrain. Similarly, it can improve adaptability to the environment. However, the requisite wheel-leg conversion device increases the structural complexity and reduces the weight-bearing capacity. The hybrid wheel-legged robot [31] has its leg structure replaced with a wheel drive that rotates in a full circle and achieves different motion gaits by controlling the phase and rotation speed of the wheel-leg, which is convenient for achieving smooth obstacle-crossing movement and simple control. A hybrid wheel-legged robot was proposed in [40], and its great motion efficiency and obstacle-crossing ability were verified. However, there is space for structure optimization to realize better strength and rigidity. Based on these latest works, we explore a new hybrid wheel-legged mobile robot by designing a novel structure of the wheel-leg.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Previous Works** & **Features** \\ \hline \multirow{7}{*}{Wheel-legged} & MAMMOTH ([PERSON] et al., 2016) & \\ \cline{2-3}  & HyTRo-I ([PERSON] et al., 2013) & \(\medmedmedmed  
Given the above background, this paper proposes a hybrid wheel-legged mobile robot that incorporates the characteristics of both wheeled and legged structures. Based on the robot's obstacle-crossing needs, the structural parameters are determined using modeling, theoretical analysis, etc. Then, the optimal wheel-leg cover material is determined using dynamic analysis, after which the prototype is made and subjected to experiments in various environments. As a hybrid mobile robot, the proposed wheel-legged mobile robot incorporates the structural advantages of wheeled and legged mobile robots. In addition to expanding the usage scenario, it realizes a relatively simple control and improves obstacle-crossing capability and movement stability, exhibiting satisfactory overall performance.