Design, Fabrication and Dynamic Testing of Insect-inspired Nano Air Vehicles

S. Grondel, D. Faux (Univ. Polytechnique Hauts-de-France, France), M. de la Bigne, A. Itawi (Univ. Polytechnique Hauts-de-France and Arts et Métiers, France), M. Zwingelstein, S. Ghenna, C. Soyer, E. Cattan (Univ. Polytechnique Hauts-de-France, France), O. Thomas (Arts et Métiers, France)

Since few years, there is a growing interest for small-scale aerial vehicles due to their very promising applications for indoor inspection. However, nano aerial vehicles are not simply smaller versions of full-size drones and there are many scientific and technological challenges to solve before they can become operational. When scaling down, a potential solution is to draw inspiration from nature and especially from the small birds and flying insect’s species to design and fabricate nano air vehicles. In this context, the aims of this work are to outline the proposed bioinspired approach and to present the different original concepts deployed to tackle such an issue, before to analyse carefully the simulated and experimental results. The first idea was to use an actuation scheme based on biomimetic principles, i.e. principles that are directly inspired by observation of flying insects. In many insects, exoskeletal deformations induce indirectly wing movements. More precisely, the thorax behaves as a damped structure where the wing joints are specialised to transmit large strain amplitude from the musculature to the wings while the scutum via indirect actuation stores and recovers elastic energy. On this basis, we proposed to use an indirect actuation based on an electromagnetic actuator and a thorax design with a concise transmission for the nano air vehicle. Moreover, the electromagnetic actuator was optimized to control the vibrating amplitudes whilst at the same time minimizing its mass. A second idea was to address the design of the elastic structure of artificial wings to reproduce insect wings kinematics. Our bioinspired kinematics relies on the original concept of using the resonant properties of the wing structure in order to combine the motion of two vibration modes, a flapping and a twisting mode, in a quadrature phase shift. One way of achieving this particular combination was to optimize the geometry and elastic characteristics of the flexible structure such that the two modes are successive in the eigenspectrum and close in frequency. For such a purpose, a semi-analytical model, based on assembled Euler-Bernoulli beams, was developed to understand, compute and optimize the artificial wing dynamic vibrations. This model has served to show that it was possible to obtain several artificial wing structures with a flapping and a twisting mode close in frequency. However, as insect wings consist of a complex geometry with supporting veins and very thin flexible membranes, it was also essential to find a technology able to realize microstructures with a high precision, a good reproducibility and with the adapted materials. To answer to this problem, the novelty was to use the standard technologies of Microelectromechanical systems. Such a technology not only allows selecting appropriate materials for the artificial wings but also paves the way to a future fully integrated micro device in the thorax, i.e. including a microcontroller and a micro battery. After an overview of SU-8 and Parylene photoresist structures and their functions in the insect-inspired nano air vehicle, we demonstrated that the prepared polymer wings were faithful to real wings in terms of both geometric properties and mechanical characteristics. Once the design of the global structure optimized through simulations, a polymeric prototype was micromachined with a wingspan of 3 cm, flexible wings and a single actuator for a total mass of 22 mg. Then a dedicated lift force measurement bench was developed and used to demonstrate a lift force equivalent to the prototype weight. Finally, at the maximum lift frequency, high-speed camera measurements confirmed a kinematics of the flexible wings with flapping and twisting motions in phase quadrature as expected. The results obtained set vibrating wing as a compelling example of lift creation present in nature, and shed light on some of the biomimetic principles used by flying insects.