RAISE: Spring & Wings: Resonance in insect and engineered flight with synchronous and stretch-activated actuation

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This Research Advanced by Interdisciplinary Science and Engineering (RAISE) project will develop a dynamical model to enhance understanding of insect flight as an integrated system and apply this information to robotic design. Flight at the size of insects is very energetically challenging. Nonetheless, the evolution of flight spurred much of the evolutionary diversity of insects we see today. Insects fly long distances, maneuver in crowded and gusty environments, and overcome the energetic limitations of flapping wing flight in ways that cannot yet be matched in human-engineered systems. Insects couple springy exoskeletons to their wings to help store and return energy on every flap; however, to maximize energy return, insects would have to beat their wings at a steady rate. This project will explore how insects couple springs and wings together to manage energy requirements and flight control under a range of conditions. This project will also explore how the two distinct types of muscle contraction that insects use to power flight could both be achieved with the same underlying mechanics and muscle properties, enabling a mathematical framework for understanding how insects achieve such different types of flight. The project will use robophysical models with springy exoskeletons coupled to wings and insect-scale flapping robots to establish a general “spring-wing” framework. Research at both collaborating institutions will include an immersive, vertically integrated undergraduate research program. Student teams will receive mentorship and on-site research experience during the school year and will travel to their exchange location for interdisciplinary summer research. At least two graduate students and a post-doctoral fellow will also receive cross-disciplinary training.Insect-scale flapping-wing flight demands both high-power actuation and low-latency control. To mitigate flight power requirements, most insects actuate their wings indirectly via muscles that deform a stiff, elastic exoskeleton. Coupling elastic elements to the wings allows insects potentially to operate as a resonant system, which would reduce power costs but also would introduce control constraints, such as limiting wingbeat frequency modulation. To power flapping flight, insects evolved two distinct actuation strategies: synchronous flight, with time-periodic forcing of antagonistic muscles paced by the nervous system, and asynchronous flight, in which muscles set up self-excited oscillations due to strain-dependent activation. The project will establish an analytic framework for spring-wing systems, test if insects operate at their hypothesized resonant frequencies, and develop a dynamically scaled robophysical spring-wing flapper to explore how a single non-dimensional parameter, the Weis-Fogh number, influences elastic energy storage and aerodynamic force control. The two muscle actuation strategies will then be combined, testing if synchronous flying insects that have evolved from asynchronous insects retain the necessary physiological signatures of self-excited (asynchronous) oscillations. A single dynamic system that can transition from the two regimes of stable flapping will be tested in the robophysical system and in an at-scale, bio-inspired flapping wing robot. Finally, the tradeoffs of operating at or away from resonance in spring-wing systems will be investigated. The project bridges the biological and physical sciences, will expand understanding of physiological and biomechanical principles and trade-offs involved in flight, and should transform the current understanding of insect flight, with applications to robotics. Undergraduate and graduate students and a post-doctoral fellow will participate in mentored, interdisciplinary research teams, and will present research results at national scientific meetings. Research results will also be disseminated through a bio-inspired design workshop. This award is co-funded by the Dynamics, Control and Systems Diagnostics Program in the Division of Civil, Mechanical and Manufacturing Innovation, Directorate for Engineering, and the Physiological Mechanisms and Biomechanics Program in the Division of Integrative Organismal Systems, Directorate for Biological Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.