On the Energy Trade-offs of Continuous vs. Locked Rotor Tilt Control in Tiltrotor Quadcopters

Unmanned aerial vehicles are increasingly used in applications where flight time is critical, making energy efficiency a central design concern. Among multirotor platforms, tiltrotor quadcopters stand out by allowing their rotors to rotate about a fixed axis, enabling direct horizontal thrust generation without tilting the entire vehicle, but they introduce a key design question: how should the tilt angle be controlled, and at what energy cost? Two broad approaches exist: fixed-tilt configurations, where the rotor orientation is held constant and maneuvering is achieved through thrust differences, and variable-tilt configurations, where the tilt angle is continuously adjusted during flight. Despite growing interest in tiltrotors, the energy implications of each approach remain largely unexamined. In our previous work, we addressed this gap by developing an online Recursive Least Squares algorithm that identifies the energy-optimal vehicle pitch trim angle in real time, reducing propulsion consumption under wind disturbances while maintaining precise position tracking. The present paper extends these results along three directions: (i) the total energy expenditure of continuous variable-tilt tracking is compared against a fixed-tilt approach, (ii) the parasitic power drain of servo actuators is explicitly accounted for, and (iii) a self-locking worm gear is proposed for the fixed-tilt approach as a practical modification for further energy savings. Bench measurements show that the worm gear draws zero current at idle (versus 0.05–0.09 A for the servo) and reduces the average actuation current by roughly 50%. To achieve precise tracking against wind disturbances, Active Disturbance Rejection Control and Incremental Nonlinear Dynamic Inversion are employed for position and attitude control, respectively. The primary trade-off is actuation bandwidth, with full-range tilt taking approximately three times longer than the servo baseline. These results characterize an overlooked energy–agility trade-off and offer a practical self-locking tilt strategy for endurance-critical missions.