## 4 Motion Simulation and Experiment of the Lunar Exploration Hexapod Robot
### Kinematic Simulation Analysis of the Lunar Exploration Hexapod Robot
#### 4.2.2 ADAMS Kinematic Simulation Analysis
The change in angular acceleration of the hexapod robot can reflect the speed of the angular velocity change between the joints of the robot in the process of linear motion, and the stability of the robot in motion can be judged by analyzing it. Figures 15 and 16 are the comparison curves of the angular acceleration of the hip and knee joints of the two groups of robotic legs in the two gaits. Through analysis, it was found that in both motion modes, the angular acceleration curves of the robot's legs exhibited periodic variations. In the traditional gait, the maximum angular acceleration of the hip joints for both leg groups was 300 rad/s2, and the maximum angular acceleration of the knee joints for the first and second leg groups was 1195.73 rad/s2 and 1389.71 rad/s2, respectively. In the \"inverted gait\" motion mode, the maximum angular acceleration of the hip joints for both leg groups was 300 rad/s2, and the maximum angular acceleration of the knee joints for the first and second leg groups was 959.67 rad/s2 and 1334.61 rad/s2, respectively. Compared to the traditional gait, the maximum peak values of knee joint angular acceleration for both the first and second leg groups were reduced by 19.7% and 3.9%, respectively. Simultaneously, the analysis revealed that in the robot's traditional gait motion, abrupt changes in signals during startup and leg phase transitions could lead to tremors, affecting the stability of the robot during operation. In contrast, the inverted gait provided an inverted body posture during startup, optimizing the robot's dynamic model and offering greater swing space for the robot's legs. The simultaneous swinging of both leg groups during motion resulted in a smoother transition of signals, making the transition between the swing and support phases more seamless. This eliminated tremors, enhancing the stability of the robot. Figure 14: Angular velocity curves of the robot’s rotating knee joints: (**a**) first group of robotic legs; (**b**) second group of robotic legs. Figure 15: Angular acceleration curves of the robot’s hip joint: (**a**) first group of robotic legs; (**b**) second group of robotic legs. The magnitude of the torque of each joint in the process of linear motion of the hexapod robot is closely related to the bearing capacity of the torque of the motor shaft, which directly affects whether the robot can move normally. Figures 17 and 18 are, respectively, the comparison curves of the robot's hip and knee torques in the two gaits. Through analysis, it was found that in the traditional gait, the maximum torques of the hip joints of the first and second groups of legs were, respectively, 1228.06N\(\cdot\)mm and 1265.28N\(\cdot\)mm, and the maximum torques of the knee joints were, respectively, 1445.88 N\(\cdot\)mm and 1288.36 N\(\cdot\)mm. In the \"inverted gait\" mode, the maximum torques of the hip joints of the first and second groups of legs were, respectively, 1118.79 N\(\cdot\)mm and 1159.45 N\(\cdot\)mm, and the maximum torques of the knee joints were, respectively, 1218.56 N\(\cdot\)mm and 1248.26 N\(\cdot\)mm. Compared with the traditional gait, the maximum torque of the leg hip joint for the first and second groups of the robot in the inverted gait mode is reduced by 8.9% and 8.3%, respectively. The maximum torque of the knee joint is reduced by 15.7% and 3%, respectively. This is because, in the inverted gait mode, the inverted posture of the robot during startup provides greater swing space for the robot's hip joints. The increased swing amplitude of the joints during subsequent motion results in larger centrifugal forces acting on the corresponding joint parts. This causes certain masses to experience larger centrifugal moments at greater distances, affecting the moment of inertia. Additionally, the variation in joint swing amplitude increases the coupling effect between the robot's joints, leading to a reduction in torque.