## 5 Experiments
### Discussion  
To analyze the sensitivity of the CBBM pitch stiffness to various parameters, we changed diameter \(D\) of the circular beam and central angle \(\theta\) of the flexible segment by fixing one parameter while varying the other. The sensitivity of the CBBM to the varied parameter was analyzed using finite element simulations.  
As shown in Figure 18, the pitch stiffness increases with the decreasing diameter. When we keep the total central angle of the bistable limb fixed (i.e., length of the bistable limb does not change), a change in the length of the flexible beam for equal lengths of the two flexible beams decreases the CBBM pitch stiffness with a lengthening flexible segment. For a fixed central angle of the flexible beam, when the diameter of the circular beam gradually changes from 204 to 194 mm, the pitch stiffness increased by 13.5%. For a fixed diameter of the circular beam, when the central angle of the flexible beam gradually changes from 4 to 9\({}^{\circ}\), the pitch stiffness decreases by 52%.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Pitch Stiffness (N \(\cdot\) mm)/Rad**} & \multicolumn{2}{c}{**FEA**} & \multicolumn{2}{c}{**Experiment**} \\ \cline{2-5}  & **Initial Position** & **Second Position** & **Initial Position** & **Second Position** \\ \hline CBBM & 698.3 & 481.1 & 744.2 & 489.9 \\ \hline SBBM1 & 607.0 & 363.9 & 621.2 & 382.3 \\ \hline SBBM2 & 634.2 & 426.3 & 645.7 & 439.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison between simulation and experimental results of pitch stiffness in different structures.  
Figure 17: Experimental curve of moment and deflection radians of bistable mechanisms.  
When the central angle of the circular beam of the bistable beam remains unchanged, the central angle of the rigid beam increases if the central angle of the flexible circular beam decreases. In other words, the length of the flexible circular beam decreases, while the length of the rigid circular beam increases. The in-plane area of the rigid circular beam is larger than that of the flexible circular beam. Therefore, reducing the central angle of the flexible circular beam increases the in-plane area of the bistable mechanism of the circular beam. This increases the ability of the CBBM to resist out-of-plane loads and increases the pitch stiffness of the CBBM. Similarly, reducing the radius of the CBBM reduces the length of the flexible beam. The shift of the CBBM mainly depends on the nonlinear deformation of the flexible beam. As the length of the flexible beam decreases, the load required for deformation increases, which increases the deformation resistance of the circular beam.  
According to the experimental results and finite element simulations, the CBBM exhibits a significant improvement in increasing the pitch stiffness. In some application scenarios where the bistable mechanism is required to be used as a sensor, the actual force received by the sensor cannot be guaranteed to be perpendicular to the plane where the bistable mechanism is located and there must be some off-axis load. When the impact of an off-axis load occurs, the CBBM allows for better motion consistency without compromising the senso accuracy.