# Event-Triggered Fault-Tolerant ADRC for Variable-Load Quadrotor with Prescribed Performance
## 1 Introduction  
With the rapid development of unmanned aerial vehicle (UAV) technology, quadrotors show broad application prospects in military and civil fields. In the military field [1, 2], quadrotors are widely used in reconnaissance and surveillance, target localization, electronic countermeasures, and other tasks; in the civil field [3, 4, 5], they play an increasingly important role in aerial photography, agriculture, logistics and delivery, emergency rescue, and other aspects. However, the quadrotor is inherently a strongly coupled nonlinear system with under-driven characteristics. Since quadrotors usually work in complex outdoor environments, they are inevitably affected by a variety of disturbing factors, including signal noise [6], bad weather [7], and so on. During mission execution, quadrotors often carry varying payloads to meet diverse requirements. As shown in Figure 1, firefighting missions require water tanks, agricultural spraying demands pesticide containers, and logistics delivery involves transporting parcels. The payload variations significantly alter the mass parameters while inducing dynamicchanges in the center of gravity and moment of inertia. These alterations affect dynamic characteristics and compromise trajectory tracking accuracy and attitude stability. Therefore, it is of great practical significance to study the stability control method of quadrotor UAVs under variable load conditions. Recent years have witnessed significant advances in quadrotor control research, primarily encompassing conventional control methods [8; 9; 10], modern control approaches [11; 12], and intelligent control techniques [13; 14]. variable-load quadrotors face control difficulties due to changing mass, shifting center of gravity, and external disturbances. Current studies primarily address these challenges through parameter adaptation and disturbance observation methods. Regarding parameter adaptive control, the scholars of [15] proposed a hybrid fuzzy sliding mode control method to ensure quadrotor stability, though its fuzzy rule processing requires considerable computation time. The study of [16] proposed a mass estimation method using least squares and sliding mode observers. However, this solution only works for situations involving gradual mass reduction during payload release, which limits its practical use. In disturbance observation and compensation, the study of [17] developed an extended state observer (ESO)-based control scheme for quadrotors carrying cable-suspended payloads, achieving effective swing reduction and improved disturbance resistance during lifting maneuvers. Quadrotors possess constrained onboard computing capabilities as flight platforms. Their control algorithms must therefore maintain strict real-time performance while ensuring computational efficiency. This creates a critical challenge in quadrotor control: how to effectively reduce computational and communication loads while maintaining control performance. event-triggered control (ETC), as an innovative control method, has gained wide attention in the UAV field [18; 19; 20]. event-triggered control offers distinct advantages through its unique triggering mechanism that enables seamless integration with various control methods, maintaining system stability while reducing computational and communication resource demands. The scholars of [21] developed a switched-threshold event-triggered mechanism integrated with an ESO, enabling intermittent velocity/disturbance observation and precise estimation while establishing a disturbance-rejection output feedback control law for trajectory tracking with guaranteed Zeno-free operation. Quadrotors may encounter various actuator failures during mission execution. Fault tolerant control [22; 23; 24; 25] means that the closed-loop system remains stable and meets certain performance specifications in the event of the failure of a sensor, actuator or component of the control system.