<![CDATA[Altitude regulation is essential for maintaining stable hovering and supporting autonomous operation in tricopter unmanned aerial vehicles (UAVs), whose asymmetric propulsion and rear-rotor tilt mechanism introduce additional control challenges. This study designs, implements, and experimentally evaluates a Linear Quadratic Regulator (LQR)-based altitude-hold controller for a Y- configured tricopter equipped with an inertial sensing module and a downward-facing ultrasonic range sensor for low-altitude feedback. Attitude stabilization was first evaluated using an indoor tuning rig before the complete system was tested under actual flight conditions. The altitude controller was evaluated at reference altitudes of 0.40, 0.85, and 1.25 m and under intentional downward disturbances at a reference altitude of 1.25 m. Across five disturbance trials, the system achieved a mean rise time of 0.513 ± 0.223 s, a mean settling time of 1.113 ± 0.313 s, and a mean steady- state error of 0.0344 ± 0.0069 m. Overshoot occurred in three trials and remained between 1.39% and 1.56%. Without intentional disturbances, steady-state errors of 0.0115, 0.0233, and 0.0064 m were obtained at reference altitudes of 0.40, 0.85, and 1.25 m, respectively. These results demonstrate that the proposed controller can maintain low-altitude hovering and recover from external vertical disturbances within the predefined performance requirements of the tested tricopter platform.]]>
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