## 4 Motion Simulation and Experiment of the Lunar Exploration Hexapod Robot
### Robot Prototype Experiment  
According to the overall mechanism design and size parameters of the lunar exploration hexapod robot, the test prototype of the robot, as shown in Figure 19, was built.  
Place the lunar exploration hexapod robot on the constructed simulated lunar soil test platform for on-site testing to validate the rationality of the overall mechanical structure design. In this experiment, the tripod gait is primarily applied to the physical prototype of the lunar exploration hexapod robot, aiming to verify whether the hollow structure of the robot's legs can enable it to stand and walk normally on the unstructured terrain of the Moon.  
Figure 20 shows the robot's standing posture in the simulated experiment chamber. In Figure 20a, it can be observed that the spherical design of the robot's foot end allows it to stand well on the unstructured terrain of simulated lunar soil. Figure 20b depicts the robot's foot in a small lunar crater, illustrating that the leg design effectively prevents sinking. Figure 20c-e display the robot's leg positions during lift-off, revealing minor lunar soil adhesion to the robot's foot after lifting, but the robot's leg movement effortlessly dislodges the soil particles from the hollow part, with the metal material effectively preventing soil adhesion.  
Figure 21 shows the physical image of the lunar exploration hexapod robot in tripod gait walking: Figure 21b represents the posture of the robot's first group of legs when lifted; Figure 21c shows the posture when the first group of legs lands; and after the landing of the first group of legs, the second group of legs lifts simultaneously, as shown in Figure 21d, achieving the forward gait of the robot through the alternating movement of the two groups of legs.  
Figure 19: Prototype of the lunar exploration hexapod robot.  
Figure 18: Robotic knee torque curves: (**a**) first group of robotic legs; (**b**) second group of robotic legs.  
Figure 21: Diagram of the lunar exploration hexapod robot walking in a straight line: (**a**) initial state; (**b**) the first group lifted; (**c**) the first group landed; (**d**) the second group lifted; (**e**) the second group landed; (**f**) the fuselage returned to its initial state.  
Figure 20: Robots in the simulation chamber: (**a**) robot’s standing posture; (**b**) simulation of a robotic foot end in a small lunar crater; (**c**) end of a foot caught in the Moon’s soil; (**d**) lunar loam attached to the end of the foot after elevation; (**e**) robot’s legs after dumping lunar soil.  
Through experiments, it has been proven that the mechanical structure of the lunar exploration hexapod robot is reasonable. The hollow structure of its legs reduces the overall weight of the robot while effectively supporting the robot's weight. This allows the robot to stand stably on the unstructured surface of the Moon. The spherical design of the foot prevents the robot's foot from sinking, enabling normal standing and walking on lunar soil. Additionally, during walking, lunar soil adhering to the legs can be easily shaken off from the hollow part through leg movements, reducing soil adhesion and achieving the purpose of the hollow design (Supplementary Materials).