Comparative Neuromechanical Wing-Actuation Architectures of Flapping Flight in Insects, Hummingbirds, and Robots

Natural fliers have evolved a diversity of neuromechanical systems to produce complex wing motion for flight, achieving a level of aerial performance not yet attainable by robotic fliers. A wing neuromechanical system encompasses wing mechanical structures, musculoskeletal actuation, central and peripheral sensorimotor circuits, proprioceptors, sensory pathways, and aerodynamic processes. This study examines the anatomical and functional attributes of flapping-wing neuromechanics in insects and hummingbirds, and provides a comparative analysis and synthesis to identify features of their integrated architectures. Two functional architectures are identified: 1) A Dual Neural-Mechanical Oscillator characterized by nested central, peripheral and mechanical feedback loops; and 2) a Neurally-modulated Mechanical Oscillator with a diminished role of the central loop and a clear separation of power and control loops. Rather than representing a strict dichotomy, these architectures are not mutually exclusive and are evolutionarily related. The actuation systems in surveyed robotic flapping-wing fliers follow a much simpler architecture, i.e., Open-Loop Mechanical Oscillator. Biological and robotic architectures are compared in terms of functional separation of power and control, emergence of rhythm, and the roles of proprioception. Finally, key attributes of wing neuromechanical systems are identified for emulation to help narrow the performance gap between natural and robotic fliers.