Shibbir Ahmed, Muhammad Yousaf Nadeem, Muhammad Zain, Zubair Iqbal, Issac Tawiah, Chengming Sun
Agricultural sprayer UAVs, variable mass, liquid slosh, PID, sliding-mode controller, attitude tracking
The stability of autonomous liquid transporter unmanned aerial vehicles (UAVs) is crucial for precision in agricultural field spraying. This paper proposes an adaptive robust control scheme designed to stabilise agricultural quadrotor UAVs affected by variable mass and liquid sloshing dynamics during pesticide application. A comprehensive nonlinear mathematical model is developed to explicitly represent UAV–liquid interactions, accounting for both liquid sloshing and time-dependent mass variations. An adaptive PI- based sliding-mode controller is proposed, featuring a neural network identifier to estimate unknown sloshing forces and a nonlinear disturbance observer to mitigate external disturbances. Theoretical analysis through designed Lyapunov functions confirms the closed- loop system’s robustness, stability, and bounded estimation errors, even despite varying liquid mass conditions. Simulation experiments validate the effectiveness of the proposed method, achieving approximately 41.4% and 53.8% in trajectory tracking accuracy, stabilisation, and disturbance rejection along the x- and y-axes, respectively, compared to the conventional proportional integral derivative (PID) counterpart. Overall, this research enhances UAV control methodologies by effectively managing sloshing-induced dynamics, thereby facilitating improved quadrotor system designs and making a substantial contribution to agricultural automation.
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