Bird-Inspired Spatial Flapping Wing Mechanism via Coupled Linkages with Single Actuator

Daniel Huczala; Sun-Pill Jung; Frank C. Park

cs.ROApr 9, 2026

Bird-Inspired Spatial Flapping Wing Mechanism via Coupled Linkages with Single Actuator

Authors: Daniel Huczala, Sun-Pill Jung, Frank C. Park

Organizations: Robotics Laboratory, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea · Biorobotics Laboratory, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea

Abstract

Spatial single-loop mechanisms such as Bennett linkages offer a unique combination of one-degree-of-freedom actuation and nontrivial spatial trajectories, making them attractive for lightweight bio-inspired robotic design. However, although they appear simple and elegant, the geometric task-based synthesis is rather complicated and often avoided in engineering tasks due to the mathematical complexity involved. This paper presents a bird-inspired flapping-wing mechanism built from two coupled spatial four-bars, driven by a single motor. One linkage is actuated to generate the desired spatial sweeping stroke, while the serially coupled linkage remains unactuated and passively switches between extended and folded wing configurations over the stroke cycle. We introduce a simplified kinematic methodology for constructing Bennett linkages from quadrilaterals that contain a desired surface area and further leverage mechanically induced passive state switching. This architecture realizes a coordinated sweep-and-fold wing motion with a single actuation input, reducing weight and control complexity. A 3D-printed prototype is assembled and tested, demonstrating the intended spatial stroke and passive folding behavior.

Figures & tables

Fig. 1: Schematic drawing of the proposed wing design. Red: linkage for spatial flapping; yellow: actuated joint; green: base link (bird body); blue: embodied (passive) linkage providing trust in the forward stroke and automatically folding itself during backward motion.

Fig. 2: Quadrilateral $p_{0\dots 3}$ in expanded configuration during downstroke.

Fig. 3: Quadrilateral $p_{0},p_{1},p^{\prime}_{2},p^{\prime}_{3}$ in folded configuration during upstroke.

Fig. 4: Front and right views comparison of planar linkage (above) and Bennett linkage with the twist given by $\alpha_{0}=10^{\circ}$ (bellow).

Panel of Figure 5 — Fig. 5: Continuous rational motion interpolating for given poses (left); line model of the Bennett mechanism (right); figures were captured in the MotionDesigner module [ 11 ] .

Fig. 6: CAD model of the flapping wing (above) with physical joint limits (red circle); 3D printed prototype in its folded (bottom left) and extended (bottom right) configurations.

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A Multimodal Tiltwing Framework for Bioinspired Aerial Robots

Krispin C. V. Broers, Sophie F. Armanini

Department of Aeronautics, Imperial College London, London, SW7 2AZ, UK

Robotic Control Aerial Robotics

Open paper AskPDF arXiv

Tailless flapping-wing micro-aerial vehicles (FWMAVs) mimic the impressive flight performance of hummingbirds, utilising unsteady aerodynamic effects. However, existing designs are still limited and purpose-built with a restricted flight envelope and poor endurance. We therefore propose an adaptable tiltwing framework enabling bioinspired aerial robots to switch between hovering flight, high-speed directional flight, and energy-efficient gliding flight. The proposed framework utilises thrust vectoring with a wide actuation range via two fully independent propulsion units, each flapping a single wing, for effective control and enhanced manoeuvrability. For this, we developed a hybrid Scotch-yoke-based flapping mechanism that ensures a symmetric motion profile with a modular design guaranteeing an arbitrarily wide flapping angle to exploit the lift-enhancing clap-and-fling effect. Additionally, we implemented a passive wing-rotation mechanism, which, in combination with our dual-wing thrust-vectoring approach, allows unprecedented wing-design freedom, unlocking potential for precise optimisation. A contactless leading-edge tracking sensor provides accurate feedback on the wing's orientation and, in the gliding mode, enables dihedral-angle control, augmenting the active wing-pitch control. Extensive testing of a propulsion unit was conducted with a six-axis force/torque sensor, demonstrating the flapping mechanism's performance while optimising transmission efficiency and the passive wing-pitch mechanism. At full throttle, the average lift force generated by a single wing, flapping with a 188° amplitude, was 21.1 gf for a small 3.1 g 1S BLDC motor. Additional tests covering the full range of the wide-angle tilting capability showed an effective thrust-vectoring control architecture with a linear and symmetric response curve of the moments generated.

Abstract

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