# Compliant Detachment of Wall-Climbing Robot Unaffected by Adhesion State
## 4 Experiments and Results
### Robot Stability on Various Surfaces with Various Slope Angles  
The most challenging task for a wall-climbing robot is stable operation on a slippery surface with a large slope angle. Motion stability experiments were carried out under these conditions to confirm the ability of OIAC to regulate detachment under different adhesion states. Teflon is one of the few materials to which speckos cannot stably adhere. PVS, used in this study, produces weak adhesion to a Teflon surface. In this experiment, glass and Teflon were used as climbing substrates with strong and weak adhesion, respectively. The climbing substrates were attached to a platform with an adjustable slope angle, as shown in Figure 5b. To evaluate the motion stability of the robot, the roll-pitch-yaw (\(\alpha\)-\(\beta\)-\(\gamma\)) attitude information and the climbing failure rate of IBSS-8 on the glass and Teflon surfaces at various slope angles were recorded several times. The standard deviation of rolling angle \(\alpha\) which can best reflect the change of normal force was calculated and used as the quantitative evaluation of the vibrations. The statistical results are shown in Figure 7.  
Figure 6: Single\(-\)limb detachment force trace and statistical results \(S(b)\) and \(S^{\prime}(b)\): beginning state of detachment under TTC and OIAC, \(S(t)\) and \(S^{\prime}(t)\): turning state of detachment under TTC and OIAC, \(S(e)\) and \(S^{\prime}(e)\): end state of detachment under TTC and OIAC). The box chart shows the statistical analysis of normal force on \(S(e)\) and \(S^{\prime}(e)\). The green triangles represent the average position. For both surfaces, the support force from the ground decreased and the roll, pitch, and yaw angle oscillation amplitudes increased with increasing slope angle. From Figure 7, we can see that the rolling angle \(\alpha\) oscillation amplitude of IBSS-8 is significantly reduced compared with the TTC method in the process of climbing on the glass surface with different slope angles. In the process of glass surface climbing, the amplitude of rolling angle oscillation under OIAC was significantly different from the amplitude of TTC under different slope angles. Due to the strong adhesive strength of the adhesive material to the glass, the normal force at the detaching end state will directly cause the robot to vibrate at the rolling angle if the peeling process is not regulated. So, comparing the average rolling angle standard deviation when climbing on the glass surface to the value on Teflon surface under the same slope angle, it is not difficult to find that, under the trajectory tracking control, the oscillation amplitude on the glass is greater than the one on the Teflon, and, under our method, the oscillation amplitudes of the two materials are basically the same; this is because, under the help of OIAC, the peeling angle at the detaching end state is close to \(\pi\), and there is little change in the normal adhesion force. Figure 7: Statistical results of robot rolling angle \(\alpha\) and the fail rate for various surfaces with various slope angles. Statistical results for (**a**) glass and (**b**) Teflon surfaces. In the box chart, the black lines represent the median position and the green triangles represent the average position. In the statistics, *** indicates a significant difference. The P value between roll under TTC and roll under OIAC on glass is \(3.43\times 10^{-5}\) for \(70^{\circ}\), \(4.26\times 10^{-4}\) for \(75^{\circ}\), \(1.1\times 10^{-5}\) for \(80^{\circ}\), \(6.84\times 10^{-7}\) for \(85^{\circ}\), and \(2.82\times 10^{-5}\) for \(90^{\circ}\). The above data strongly prove that, no matter the size of the adhesion load and the current slope angle, OIAC can effectively regulate the peeling angle and adhesion strength. During gecko movement, the force increment in the toe detachment process does not change significantly because of the change in the external load, which greatly contributes to movement stability.