# Vision-Guided Hierarchical Control and Autonomous Positioning for Aerial Manipulator
## 5 Experimental Results
### Attitude Analysis of the Aerial Manipulator  
Rotary-wing UAVs are complex, nonlinear, and underactuated systems. When equipped with a manipulator to perform tasks, the system's dynamics are influenced by factors such as motion velocity, angles, and payload mass. This can cause deviations in the attitude and positioning of the UAV, leading to mission failures, accidents such as collisions with the ground, and even crashes. Therefore, in this study, flight data was recorded to execute the five operational motion poses. The attitude information of the UAV was analyzed and compared before and after mounting the operational aerial manipulator. This analysis aimed to validate the operational stability of the proposed aerial manipulator system.  
As shown in Figure 15, the aerial manipulator took off from 0 s to 8 s and moved along an autonomous navigation path in search of a target object. During the motion, the UAV's attitude angles exhibited relatively small fluctuations before and after mounting the manipulator, which fell within the normal range of attitude angle variations for indoor flights. Between 9 s and 21 s, the UAV reached the target object and visually guided itself toward it. The manipulator descended vertically into the pre-grasping pose. Due to the disturbances caused by the manipulator, the center of gravity of the entire flight system can change, resulting in dynamic instability and slightly larger fluctuations in the attitude angles. However, the roll and yaw angles had relatively smaller fluctuations. With the manipulator, the range of fluctuation for the roll angle was within \(\pm 4^{\circ}\), and the range for the yaw angle was within \(\pm 2.5^{\circ}\). However, the pitch angle exhibited larger fluctuation within \(\pm 5^{\circ}\). This was due to the movement of the manipulator in the XOZ plane from the initial pose to the pre-grasping pose, significantly affecting the pitch angle stability of the aerial manipulator system.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Attitude of the Aerial** & \(\theta_{1}\) (Pitching) & \(\theta_{2}\) (Grasping) \\
**Manipulator with Operation** & \(\theta_{1}=0^{\circ}\) & \(\theta_{2}=70^{\circ}\) \\ \hline \(\text{Initial pose}\) & \(\theta_{1}=90^{\circ}\) & \(\theta_{2}=70^{\circ}\) \\ \(\text{Pre-grasping pose}\) & \(\theta_{1}=75^{\circ}\) & \(\theta_{2}=45^{\circ}\) \\ Flight pose in operation & \(\theta_{1}=115^{\circ}\) & \(\theta_{2}=45^{\circ}\) \\ Delivery pose & \(\theta_{1}=75^{\circ}\) & \(\theta_{2}=70^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: The angle values of the two servos.  
Between 22 s and 30 s, the aerial manipulator entered the state of grasping the target object. Compared to the state without the manipulator, the presence of the manipulator resulted in larger variations in the attitude angles due to the weight of the grasped object. In particular, the pitch angle experienced fluctuations, however, generally remained within \(\pm\)5\({}^{\circ}\) for control. The mechanical gripper completed the grasping action before and after 22 s (as indicated by the red circle in Figure 15). Subsequently, the aerial manipulator ascended to the operational flight pose, reached the target location for delivery, and landed at the destination. Throughout the flight process, the variations in the attitude angles can be controlled within \(\pm\)5\({}^{\circ}\), which falls within the normal fluctuation range. This also demonstrates the good stability of the designed operational aerial manipulator system.  
In summary, the aerial manipulator system designed in this study can generally ensure the global stability of the system during flight operations in the five poses. It can respond to external forces caused by grasping the target object, allowing the UAV to maintain stability. Additionally, it does not produce significant position drift and exhibits robustness in underactuated conditions.