## 1 Introduction  
Mobile robots are intelligent systems that integrate various functions, including environmental perception, dynamic decision-making and planning, behavior control, and execution. These robots find wide applications in various fields, such as rescue, reconnaissance, and military operations. Based on their mode of mobility, mobile robots can be classified into four broad categories [1], namely, wheeled robots, legged robots, tracked robots, and composite structural robots. The walking mechanism of wheeled mobile robots is relatively simple, with wheels as the main body. They possess advantages, such as high efficiency, being lightweight, and ease of control, but their environmental adaptability is weak, making it difficult for them to navigate structured environments, such as staircases. Legged mobile robots are highly adaptable to their surroundings and can adjust their leg posture to traverse rugged terrains. However, these robots tend to have complex postural control and mechanisms, owing to their complex structure. Crawler robots boast a relatively stable structure and can move steadily over uneven surfaces. Unlike wheeled robots, they consume much power, owing to higher friction resistance, which limits their maximum speed. Composite mobile robots bring together two or more basic forms to achieve higher overall performance and can scale special terrain. As such, composite robots are currently the focus of much scholarly research. Some of the more common composite robots include: (1) wheel-leg composite mobile robots [2, 3], which combine the stability of wheeled robots with the strong obstacle-crossing ability of leg robots; (2) wheel-track composite mobile robots [4], which employ wheels for high-speed long-distance movement and tracks for adaptation to various complex terrains, thereby enhancing overall environmental adaptability; and (3) wheel-track-leg composite mobile robots [5], which combine even more factors and have a more complex structure. By combining the efficiency of movement on flat ground with the ability to negotiate complex terrain, wheel-tracked composite mobile robots have gained widespread attention and use. The performance of mobile robots on land is reflected in their posture, ability to cross obstacles, and movement stability [6]. Several scholars have designed and analyzed the terrestrial performance of various types of robots. [PERSON] created a versatile platform that combines tracked motion on irregular and yielding terrain, energy-efficient wheeled motion on flat and compact surfaces, and stair climbing/descending capabilities. Unfortunately, the platform's gait becomes overly complicated and inefficient while ascending stairs due to its limited swing arms of only two [7]. [PERSON] studied the relationship between the position of the center of gravity of the crawler-type mobile robot and the height of the step that can be climbed [8]. [PERSON], et al., designed a wheel/track morphological reconfigurable mobile robot and established the relationship between the robot and the height of the step pendulum angle and the step height h for climbing obstacles, as well as the maximum slope that can be climbed. However, the robot's structure is overly complex and requires a specialized wheel/track conversion device for implementation [9]. [PERSON] et al., analyzed the crucial movements for their self-designed amphibious delivery robot on water and land. However, the robot's large body mass (resulting from the swing arm wheel being the same size as the main wheel) and the overly complicated and inefficient gait when climbing stairs are due to structural limitations [10]. [PERSON], [PERSON], et al., proposed an adaptive wheel-legged shape reconfigurable mobile robot and conducted a kinematics analysis of the robot's ability to climb obstacles, stairs, and gullies. However, the robot's structure remains somewhat complex, and the analysis of only two wheels failed to determine its load capacity [11].