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This research work focuses on the development of a dynamic flapping wing actuation mechanism for bat-like micro drone, based on Shape Memory Alloy (SMA) wires combined with compliant beam joints. The SMA wires' unique properties enable the robot to achieve wing flapping, mimicking movements of natural bat wings, with almost zero cost in terms of weight and occupied volume. The idea is to implement SMAs in an agonist-antagonist muscle-like configuration, paired with compliant beam joints at the shoulders of the wings, exploiting the resonance frequency of the beam and wing inertia. The study utilizes 50 micrometer diameter SMA wires strategically integrated into the bat structure, which has a total weight (considering body, actuators, and electronics besides power supply) of approximately 20 grams. The results demonstrate that the drone can achieve a substantial wing-span flapping amplitude of 80° at a frequency of 5 Hz without the need for any external cooling systems. This achievement is particularly significant given the well-known limitations of SMAs in high-frequency actuation tasks. By exploiting the resonance of the compliant beam joint, designed to have a specific natural frequency, the drone also features improved energy efficiency at the designated flapping speeds, comparing to a normal hinge joint. In conclusion, the research showcases the large potential of SMA micro-wires in enhancing performance and characteristics of robotic bio-inspired systems, particularly when combined with mechanical structures which can help overcome its limits. The achievement opens doors to significant improvements in the field of flying biomimetic micro-structures, promising exciting possibilities for future applications in surveillance, exploration, and environmental monitoring.
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