Springy Shells, Pliant Plates and Minimal Motors: Abstracting the Insect Thorax to Drive a Micro-Air Vehicle

The skeletons of the wing-bearing segments of advanced insects show unexploited potential in the design of biomimetic flapping MAVs. They consist of thin, springy, composite shells, cyclically deformed by large, enclosed muscles to flap the wings as first-order levers over lateral fulcra. The wings are light, flexible, membrane-covered frameworks, with no internal muscles, whose deformations in flight are encoded in their structure; they are ‘smart’ aerofoils. Both thorax and wings are apparently resonant structures, storing energy elastically, and tuned to deform appropriately at their operating frequencies. The form of the basic wing stroke is determined structurally, but is modulated by a series of controlling muscles, contracting tonically to alter the positions of skeletal components over the course of several stroke cycles. Fuel economy through lightness, low wing inertia and cyclic energy storage are all desirable in a flapping MAV. Furthermore, the insects’ peculiar combination of structural automation with modulation has great potential in achieving versatile kinematics with relatively few actuators. Aspects of the thoracic functioning of an advanced fly can be simulated in a simple card flapping model, combining the properties of a closed four-bar linkage with the elastic lateral buckling of a domed shell. Instructions for building this are included. Addition of further degrees of freedom, along with biomimetic smart wings, would seem to allow other crucial kinematic variables to be introduced and controlled with minimum actuation, and ways are suggested how this might be achieved in a sophisticated mechanism.