# Development of an Autonomous Underwater Helicopter with High Maneuverability
## 5 Experiments and Results  
To test the maneuverability of AUH, the horizontal linear motion experiment, horizontal rotation motion experiment and vertical lifting experiment of AUH were carried out respectively in a static pool. In the horizontal linear motion experiment, only a pair of horizontal propellers were used to make AUH move in the horizontal plane. The experiment was carried out in a pool that was 1.4 m deep and 50 m, with slight waves. The aim of this experiment is to determine the velocity and attitude of AUH under different thrust. In four sets of experiments, we set the control code of propellers' output as 50, 100, 150, 200, respectively. The corresponding output force is 0.7 N, 1.3 N, 2.2 N, 3.2 N according to the performance of the propeller. The speed of each two recording points is calculated by the shore marking point timing, and the distance between every two recording points is 1 m. At the same time, a built-in nine-axis attitude sensor is used for attitude measurement and recording. The experimental  
Figure 9: Control block diagram of (**a**) horizontal propellers; (**b**) vertical propellers; (**c**) buoyancy adjustment system. results are shown in Table 2. According to the results, the trend diagram of thrust and AUH velocity is obtained as shown in Figure 10. The curve form basically accords with the relationship between resistance and speed, and it can be seen that the maximum thrust 38 N propeller is enough for AUH to reach the designed speed of 0.8 m/s. It is easy to see from the table that no matter what the thrust is, AUH can basically enter the target speed within 1 m and maintain a uniform motion, which indicates that AUH has high linear motion maneuverability. The horizontal motion attitude recorded by the attitude sensor is shown in Figure 11. When only the horizontal propellers were turned on, AUH appeared pitch vibration. In addition, with the increase of thrust, the frequency and amplitude of vibration also increased. Although the of F = 2.2 N and F = 3.2 N groups had finished running before they were stable, it could be seen from the F = 1.3 N group that the pitch oscillation was a damped vibration, and that it eventually maintained a fixed non-zero pitch angle. This is consistent with the theoretical analysis in Section 2, in which vertical propellers are important for maintaining high maneuverability. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & **Point** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & \\ \hline \hline \multirow{2}{*}{**Fx**} & \multirow{2}{*}{**No. **} & \multicolumn{8}{c}{**Time between Two Points (s)**} & \multicolumn{8}{c}{**Average**} \\  & & & & & & & & & & & **Velocity (m/s)** \\ \hline \multirow{2}{*}{0.7 N} & 1 & 16.0 & 11.8 & 10.2 & 10.0 & 9.9 & 9.8 & 10.3 & 11.6 & 10.7 & 0.09 \\  & 2 & 17.5 & 11.7 & 10.6 & 9.5 & 10.3 & 9.5 & 9.3 & 10.3 & 10.4  
Figure 11: The pitch angle of horizontal motion experiments when F is (**a**) 0.7 N; (**b**) 1.3 N; (**c**) 2.2 N; (**d**) 3.2 N.  
To test the effect of the vertical thruster on smooth horizontal motion, the third group of working conditions with the greatest change in pitch angle is selected as the basic working condition, that is, the thrust of the horizontal thruster is maintained at 3.2 N. The results are shown in Figure 12. Compared with the case without the vertical thruster, the vibration amplitude of the pitch angle decreases significantly. It can be seen that the vertical thruster has an obvious effect on the smooth horizontal motion. The purpose of the horizontal rotation experiment was to verify the zero radius rotation ability and explore the rotation response of the AUH, so as to demonstrate its maneuverability. The horizontal rotation experiment used the AUH to maintain a fixed heading direction. The AUH automatically rotated an angle and maintained it. The variation of the yaw angle during rotation was recorded by an attitude sensor.