## 2 Structural Analysis of the Reconfigurable Wheel-Crawler Integrated Walking Mechanism  
The complex and unpredictable terrain of cement roads, wetlands, gravel, snow, ice, grassland, muddy land, steep slopes, and steps in the Qinghai-Tibet Plateau Namco Research Station requires the walking mechanism of the scientific research robot to have high mobility. The wheel base of the robot is 750 mm, the wheel base is 540 mm, the height of the chassis from the ground is not less than 170 mm, the robot load is 25 kg, and it can adapt to the above, unstructured terrain environment. The maximum moving speed is 3 km/h, the maximum climbing angle is 30\({}^{\circ}\), the maximum width across ravines is 300 mm, and the obstacle clearance height is not less than 150 mm. According to the above requirements,the robot's walking mechanism not only needs to have a fast-moving speed but also a good ability to traverse unstructured terrain. Through a comparison of the performance and structures of wheeled, tracked, and wheel-crawler combined walking mechanisms, a design scheme for a reconfigurable wheel-crawler integrated walking mechanism was proposed here.  
The reconfigurable wheel-crawler integrated walking mechanism designed in this study is modular, the reconfigurability of which is composed of a rotary driving system, a deformation positioning system, a deformation linkage system, and three sets of swing arm systems, as shown in Figure 1. The rotary driving system mainly consists of a driving motor, a gear set, a hollow shaft, tooth gears, and a belt wheel. To further improve the level of its modularity, the driving motor has an inverted design, which is built into the hollow shaft, passing the torque to the hollow shaft through the gear set and then outputting the driving torque through the hollow shaft. The re-configurable framework consists of a deformation positioning system, a deformation linkage system, and the swing arm system, including a positioning motor, a locking gear, a push rod, a thrust ring, a sliding ring, a small link rod, a bracket, a belt wheel, a drive shaft, a swing arm and a crawler belt outside the swing arm.  
The reconfigurable wheel-crawler integrated walking mechanism achieves the purpose of switching between circular wheel mode and triangular crawler mode without changing the working parts through the integration of the components of the wheel and track configurations, as shown in Figure 2, relevant videos are provided in the Supplementary Materials. When passing across a flat road, the robot can move quickly and cross obstacles effectively by switching to the circular tire mode. When passing through unstructured terrains such as sand, snow, and muddy roads, the robot can pass through a variety of terrain types smoothly by switching to the triangular crawler mode. At the same time, the length of the track is basically unchanged in the two modes (the wheel and the triangular crawler), which effectively reduces the requirements for the elastic deformation performance of the track and reduces the wear of the track.  
Figure 1: Structural diagram of the reconfigurable wheel-crawler robot.  
As the key component of the reconfigurable wheel-crawler integrated walking mechanism in contact with the ground, the crawler that is wrapped on the outside of the walking mechanism plays an important role in the interaction force and the transmission of torque between the walking mechanism and the ground. The triangular crawler mode is the main mode of the reconfigurable wheel-crawler integrated walking mechanism passing through unstructured terrain, and the structure of the crawler, especially the parameters of the grouser, has a strong influence on its tractability. To improve the trafficability of the walking mechanism on unstructured terrain, it is necessary to conduct further research on the grouser effect.