Pend-Copter: A High-Stability Vector-Thrust Bicopter UAV Driven by Torque Pendulum

Bicopter uncrewed aerial vehicles (UAVs), which have attracted increasing attention due to their compact size and high efficiency, most commonly adopt the vector-thrust configuration. For such a design, the height difference between the vector-thrust tilting axis and the center of gravity (CoG) leads to undesirable nonminimum phase nature, attitude response lag, and inadequate stability. To address these open challenges, this article develops a novel vector-thrust bicopter UAV, namely, Pend-Copter, driven by the animal-tail-inspired reaction torque pendulum. In particular, a reaction torque pendulum is introduced for UAV attitude control for the first time, eliminating nonminimum phase characteristics by aligning the vector tilting axis center, the pendulum pivot, and the airframe’s CoG. Furthermore, within the nonlinear model predictive control framework, decoupled control of longitudinal position and pitch attitude was achieved using vector thrust and the torque pendulum, respectively. This enables the Pend-Copter to maintain attitude stability during external disturbances or large-scale positional maneuvers. In the pendulum system, the original power battery was utilized directly as the counterweight to minimize additional weight; a brushless servo motor, with no reduction gear and near-zero resistance torque, functioned as the pendulum actuator to provide a more accurate pitch moment. Flight test results demonstrate that the proposed torque-pendulum control method significantly outperforms the conventional vector-thrust control scheme in terms of attitude stability, disturbance rejection, and trajectory tracking accuracy.