# Design and Research of a Flexible Foot for a Multi-Foot Bionic Robot
## 5 Prototype Experiments and Results Analysis  
### Robot Static Attitude Test  
Appropriate prototype is selected for experiment, and parameters of robot prototype are shown in Table 3. In the prototype experiments, this paper adjusted the different postures of the robot on the same ground environment and observed the contact between the foot end of the robot and the ground. As shown in Figure 10, the robot stood in different postures, which kept the foot end in surface contact with the ground, ensuring that the robot was stable under static posture.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Structure Parameter** & **Symbol** & **Values** & **Unit** \\ \hline length of cxa & \(l_{1}\) & 75 & mm \\ length of femur & \(l_{2}\) & 105 & mm \\ length of tibia & \(l_{3}\) & 145 & mm \\ angle of latocalcaneal joint & \(\theta_{1}\) & \(-\)45–45 & \\ angle of hip join & \(\theta_{2}\) & \(-\)45–90 & \\ angle of keen join & \(\theta_{3}\) & \(-\)120–0 & \\ quality of coxa & \(\mathrm{m}_{1}\) & 0.042 & kg \\ quality of femur & \(\mathrm{m}_{2}\) & 0.044 & kg \\ quality of tibia & \(\mathrm{m}_{3}\) & 0.040 & kg \\ height of center of gravity & \(\mathrm{H}\) & 50–140 & mm \\ total mass & \(\mathrm{G}\) & 2.01 & kg \\ \hline \hline \end{tabular}
\end{table}
Table 3: Robot parameters.  
In order to verify the accuracy and reliability of the foot-to-force perception, the following experiment was designed.  
The robot was placed as shown in Figure 10. The legs on the right side of the figure are leg1, leg3, and leg5 from front to back; the legs on the left side of the figure are leg2, leg4, and leg6 from front to back. In the four-legged state (i.e., leg1-leg4 as the supporting legs), since leg3 and leg4 are in the center of the robot and need to bear the weight of leg5 and leg6, leg3 and leg4 are theoretically subjected to more force than leg1 and leg2. Since the perception of the foot force was presented by the voltage output of the sensor, the difference of the force at the foot end was small. In order to make the experimental results more obvious, the DC stabilized power supply was used to supply 5 V, and the acquisition card was adjusted in a high-speed manner. The measurement accuracy was adjusted to 6, that is, we kept six digits after the decimal point, and the sampling speed was 34,723.4 sps. The FSS voltage curves of leg 1 and leg4 were recorded, the load was added at the centroid position of the robot, and the centroid position of the robot was pressed irregularly. The voltage curve was recorded as shown in Figure 11.  
As can be seen from Figure 11, whether a load, no load, or irregular pressure was applied, the voltage value of leg4 was always slightly lower than the voltage value of leg1, that is, the force of leg4 was always slightly larger than the force of leg1, which was consistent with the actual force of the foot end. Thus, the force situation was consistent.  
In the hexapod support state, we adjust the position of the center of gravity of the robot to shift it toward the direction of leg4, as shown in Figure 7b. The force of leg4 increases with the shift of the center of gravity. As the center of gravity adjustment ends, the foot-end voltage returns to a stable state, which was in line with the actual force of the robot. At the beginning of the robot's initial adjustment, the robot suddenly starts moving from a standstill and was constantly adjusted during this process, causing the foot voltage to be unstable.  
Figure 11: Voltage variation curve of leg1 and leg4 in quadruped support stage.  
Figure 10: Different postures of robot. (**a**) Quadruped support; (**b**) left shift of center of gravity; (**c**) hexapod support on slopes; (**d**) upstairs.  
The experimental results in Figure 12 show that the robot's foot was relatively accurate in the magnitude of the force, and the force magnitude correctly reflected the trend of the robot's attitude change. It satisfied the requirements of the robot in the static state for accuracy and reliability of the foot end.