# Research on the Posture Control Method of Hexapod Robot for Rugged Terrain
## 5 Simulation and Experiment
### Posture Control Experiment on Unstructured Terrain  
The purpose of the posture control experiment is to verify the ability of the hexapod robot HITCR to traverse complex terrain under the control of the posture controller and the effect of the gravity center position control method based on foot end force distribution on improving walking stability. The terrain is planned to analyze the effects of the slightly rugged terrain posture maintenance and the severely rugged terrain posture adjustment, as shown in Figure 18. The terrain is divided into three parts: flat, lightly rugged, and heavily rugged. The rugged terrain is paved with angular gravel and stones of different sizes and roughness, and the protruding terrain is piled up in the severely rugged part. The maximum height of the protruding relatively flat terrain is about 210 mm.  
Figure 17: Foot trajectory simulation in MATLAB: (**a**) Adaptive foot-end trajectory in a cycle, (**b**) projection of trajectory in XY, (**c**) projection of trajectory in the XZ plane, and (**d**) projection of trajectory in the YZ plane [29].  
Figure 18: Staged unstructured terrain.  
Figure 19 shows the process screenshot of the robot crossing the terrain. As shown in (a), the robot enters the slightly rugged terrain after two walking cycles, and the maximum obstacle height of the terrain is less than 40 mm, so the posture maintenance strategy is selected. As shown in (c), the robot enters the heavily rugged terrain after another 12 walking cycles, and in (d) the foot falls on a stone with a height of about 50 mm. This behavior can stimulate the posture adjustment strategy of the severely rugged terrain. The robot climbs the convex terrain in (e) and finally crosses the complex terrain in (f). Therefore, the experimental results verify the effectiveness of the posture controller and the walking ability of the HITCR in rough terrain.  
The observed values of pitch angle and roll angle are shown in Figure 20a,b, respectively. Under the two conditions, the robot can successfully cross the staged unstructured terrain through the posture maintaining strategy and the posture adjustment strategy and adjust the posture of the trunk according to the changes of the terrain in the severe rough stage. The results show that the pitch angle and roll angle have a smooth, small fluctuation under the condition of the posture controller based on the VSDM model, but the pitch angle and roll angle have a large fluctuation under the condition of no posture controller based on the VSDM model. The effect of keeping the trunk horizontal in mild rough terrain is poor. The maximum angle offsets of pitch angle and roll angle are 5.2\({}^{\circ}\) and 4.9\({}^{\circ}\), respectively. The posture controller based on the VSDM model is like a low-pass filter, which can filter out external environment interference and unstable factors of the robot's own motion and improve the stability of the motion on the basis of realizing the target motion.  
Figure 19: Posture control experiment on staged unstructured terrain.  
Figure 20: The observed values of pitch angle and roll angle: (**a**) Curve of pitch angle, and (**b**) curve of roll angle.