# Research on Amphibious Multi-Rotor UAV Out-of-Water Control Based on ADRC
## 1 Introduction  
As a new type of robot, the amphibious multi-rotor UAV offers groundbreaking advantages over traditional UAVs and single-medium robots as they can operate continuously across multiple scenarios [1; 2; 3; 4], making them a research hotspot in various countries [5; 6; 7; 8]. However, they face the challenge of spanning different mediums and coping with the physical differences between water and air, as well as the interference of external factors such as water flow, wind, and waves. These changes can lead to variations in control model parameters. Traditional cross-medium control methods have low robustness and have difficulty in maintaining system stability when encountering complex environments, leading to cross-medium failure. The cross-media technology of amphibious multi-rotor UAVs is a key area of research, and numerous scholars have made significant contributions to this field. In 2014, [PERSON] et al. [9] proposed a two-stage approach to the spanning process, dividing it into airborne and underwater phases, and designed a corresponding dynamics model. They also established a simulation control system using a PD controller and verified the feasibility of their approach. In 2015, [PERSON] et al. [10] proposed a switching approach to cross-media control, with separate robust controllers for air and underwater media. However, theirmethod did not consider the variation in added mass and float, leading to limitations in seamless cross-media control. In 2015, [PERSON] \(Z\) et al. [11] designed a physical model of a symmetric cylindrical vehicle for an amphibious trans-media vehicle and investigated the underwater dynamics of the vehicle. In 2016, [PERSON] [12] and others, inspired by birds, invented a deformable winged aircraft that can dive from the air into the water and verified its feasibility through experiments. In 2016, [PERSON] et al. [13] developed a power system with independent air and water thrusters using ADRC technology to achieve attitude and altitude control during water entry. The results of the study show that the controller has better control performance than the traditional PID controller. In 2018, [PERSON] et al. [14] designed and experimentally validated an adaptive sliding mode controller to reduce the effect of parameter uncertainty on aircraft stability. In 2018, [PERSON] et al. [15] designed a hybrid controller for the trajectory tracking of an air-submerged motion system for an air-air amphibious multi-rotor vehicle based on the hybrid control system concept, and experiments confirmed that the hybrid controller can effectively accomplish trajectory tracking. In 2019, [PERSON] et al. [16] introduced a small unmanned underwater vehicle (UUAV) similar to the conventional quadcopter and proposed a strategy to break the calm water surface. However, the paper clarifies the point that further analysis of underwater dynamics in submerged and transition states should be carried out. In 2020, [PERSON] et al. [17] designed a PID controller based on an RBF neural network with real-time rectification parameters for trans-media vehicles, achieving better robustness in attitude angle control than the traditional PID controller. In 2021, [PERSON] et al. [18] designed an unmanned aircraft capable of rapid multiple transitions across media based on the hybrid design concept for the interface media spanning problem and verified their approach through experiments. In 2021, [PERSON] et al. [19] designed a single-input FUZZY P + ID controller to stabilize air and underwater attitudes and achieve the seamless docking of cross-media processes. Most recently, in 2022, [PERSON] et al. [20] developed a proportional-integral-derivative (PID) controller based on a genetic algorithm (GA) and radial basis function (RBFNN) based on the cross-media process of water-air vehicles and compared the performance of the two controllers through simulations. More introductions and research on amphibious robots and amphibious multi-rotor UAVs can be seen in the literature [21; 22; 23].