Design, control, and experimental validation of a cable-driven adaptive telescopic landing system for quadrotors

This paper presents the design, modelling, control, and experimental validation of a cable-driven telescopic landing system for quadrotor unmanned aerial vehicles operating on uneven terrain. The mechanism uses a 1:1 cable–pulley transmission that doubles effective actuator stroke from 35 mm to 70 mm per leg, while a passive spring-return element removes the need for bidirectional actuation, reducing complexity, weight, and energy consumption. Nonlinear effects due to cable compliance and Coulomb friction are modelled and incorporated into control design. A quasi-static force analysis is used to evaluate actuator requirements, showing a limited but sufficient safety margin under conservative loading conditions. The control architecture combines a one-dimensional Kalman filter for attitude estimation with a PID-based leg adjustment controller, together with a geometric mapping between leg extension and vehicle attitude. A rotor disarm strategy decouples attitude stabilization from ground contact dynamics during touchdown. Experimental validation over 20 consecutive landings on inclined surfaces achieved a 100% success rate. Final attitude errors were 1.2°± 0.7° in pitch and 1.4° ± 0.8° in roll, with a stabilization time of 6.3 ± 2.1 seconds after disarm. Noise analysis indicates that IMU uncertainty contributes less than 7% to total error. Results demonstrate the effectiveness and robustness of the proposed landing system for precision UAV inspection and photogrammetry applications.