# Research on Amphibious Multi-Rotor UAV Out-of-Water Control Based on ADRC
## 4 Controller Design
The fluctuation range of the ADRC control curve is \([0.95m,1.08m]\), the minimum amount of fluctuation in the three controllers, and there is no overshoot when the UAV just reaches the desired altitude. In the form of disturbing external force as a sinusoidal signal, the fluctuation trend of the ADRC curve is not obvious compared with PID and SMC, which also shows the strong anti-disturbance property of the ADRC algorithm. Furthermore, to verify the usability of the ADRC algorithm in an actual control, a control research process of ADRC is further carried out for the prototype of the amphibious multi-rotor UAV, as shown in Figure 8. In Figure 8, all electrical components are placed in a cylindrical waterproof compartment of acrylic material, and perforated screws are used to connect the wires to the inner and outer elements, and finally the gaps in the perforated screws are filled with waterproof glue to prevent water leakage. In addition, the brushless motors used in the prototype can work normally in water. The total memory of the ADRC controller is about 1881 KB, and it has high scalability. To verify the usability of the ADRC algorithm in a practical control, the amphibious multi-rotor UAV is placed at a depth of 1 m underwater, and the initial attitude \(\phi=0^{\circ}\), \(\theta=0^{\circ}\), \(\psi=49^{\circ}\) is set. In the state of the body so set, the controller built with PID, SMC,  
Figure 8: Experimental prototype of an amphibious multi-rotor UAV. Figure 7: Comparison of simulation results of PID, SMC, and ADRC outgoing water motion height control. From the experimental results in Figure 10, it can be found that near 3 s, i.e., when the amphibious multi-rotor UAV is out of the water transition, the attitude of the UAV has a more serious jitter due to the buoyancy and hydrodynamic force and the weight of the water attached to the airframe. ADRC allows the UAV roll angle and pitch angle jitter to be controlled between 6\({}^{\circ}\) and 5\({}^{\circ}\). SMC can make the UAV roll angle and pitch angle jitter be controlled between 11\({}^{\circ}\) and 10\({}^{\circ}\). The PID allows the UAV roll angle and pitch angle jitter to be controlled between 17\({}^{\circ}\) and 27\({}^{\circ}\). It can be found that ADRC still shows strong control performance in the actual control and can achieve good attitude control to ensure the stable completion of the water exit movement. SMC performance can also meet the actual control needs, but the anti-interference is weaker compared to ADRC. PID has the worst performance, and in the actual process, the PID attitude control may cause the fuselage to tilt excessively, making the propeller hit the horizontal surface, causing the UAV to flip sideways and fall into the water, leading to the failure of the out-of-water movement. From the comparison of the experimental results of out-of-water motion in Figure 11, PID, SMC, and ADRC have completed the out-of-water motion of the amphibious multi-rotor UAV. However, the PID algorithm has a significant overshoot of 0.2 m; the SMC is slower and reaches the desired height at 4.5 s, but there is no significant overshoot, and the control curve is smoother; the ADRC reaches the desired height at 4 s and there is no overshoot, and the control curve is very smooth. Based on the out-of-water motion control of an amphibious aircraft, it can be seen that before reaching z = 0, since the model parameters did not change significantly and the controller parameters were adjusted to the optimal condition for the experiment, the control curve of the three control algorithms, PID, SMC, and ADRC, all showed a certain anti-interference ability against external disturbances. When the aircraft reaches z > 0, the force situation changes dramatically, and the PID controller curve jumps up and down at 3 s, indicating the aircraft wobbles at the water-air interface, which may lead to the amphibious aircraft's rotor flaps to the horizontal plane resulting in the amphibious aircraft rolling over and falling into the water.