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Inspiration from Nature: Wing Dynamics in Robotic Systems

Insights from EPFL and Konkuk University

• Numerous flying robotic systems draw inspiration from the wing dynamics of animal species. Birds and bats typically employ their pectoral and wing muscles for wing flapping, whereas the intricacies of insect wing movements are not yet fully understood.

• Scientists at EPFL and Konkuk University have explored how rhinoceros beetles, herbivorous insects, deploy and retract their wings. Their findings, published in Nature, inspired the development of a flapping Microrobot that passively deploys and retracts its wings without requiring extensive actuators.

Theoretical Models and Methodologies

• 'Theoretical models suggest that beetles, like other insects, employ thoracic muscles at the wing bases for active wing deployment and retraction, similar to avian and chiropteran species,' Hoang-Vu Phan, the lead author, conveyed to Tech Xplore. 'Nevertheless, current methodologies for monitoring muscular activity fall short in determining the specific muscles involved and the detailed mechanics of these actions.'

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Beetle Hindwings: Nature's Origami

• Beetle hindwings, which resemble foldable origami constructs, are neatly folded and tucked under the elytra (the hardened forewings) when at rest, and passively deployed during flight. Numerous prior studies seeking to mimic beetle wing mechanics in robotic systems have used origami-inspired designs, frequently neglecting the kinematics at the hindwing bases.

• Phan explained, 'This research is an extension of my 2020 study published in Science, Where we uncovered the shock-absorbing properties of rhinoceros beetles' hindwings during collisions in flight. In the course of experiments, I accidentally documented a full two-phase wing deployment, prompting me to ponder why the beetle would use such an intricate process if governed by active muscles.'

Passive Mechanisms in Rhinoceros Beetles

• In his earlier studies of rhinoceros beetles, Phan discovered that these insects utilize their elytra and flapping forces to passively extend their hindwings for flight. Upon landing, they use the elytra to fold the hindwings back onto their body. Both processes are passive, requiring no engagement of thoracic muscles, unlike the flight mechanisms of birds and bats.

Flapping-Wing Robot Innovation

• "Implementing this passive mechanism into flapping-wing robots allowed us to demonstrate a unique feature for the first time: unlike current flapping robots that keep their wings fully extended, our robot can fold its wings along the body when at rest and passively deploy them for takeoff and stable flight," said Phan.

• The researchers applied their insights from rhinoceros beetle studies to construct an 18-gram flapping microrobot. This microrobot, approximately twice the size of a genuine beetle, is designed to passively deploy and retract its wings.

Simplified Mechanisms and Applications

• "To simplify the mechanism, elastic tendons at the robot's armpits enable passive wing closure," Phan stated. "The robot's flapping motion allows it to deploy its wings passively for takeoff and maintain flight, while cessation of flapping after landing facilitates rapid and passive wing retraction to the body, eliminating the need for extra actuators."

• Phan and his research team have recently uncovered that beetles deploy and retract their hindwings through passive mechanisms, without muscle involvement. Their findings have led to the introduction of an effective strategy for replicating these mechanisms in microrobots, thereby enhancing their insect-like characteristics.

Search and Rescue Potential

• According to Phan, the foldable-wing robot is well-suited for search and rescue missions in constrained environments. It can penetrate collapsed buildings inaccessible to humans due to its small size, enabling it to maneuver through narrow openings. Upon landing, it can switch to crawling or other locomotion modes when flight is not feasible.

• Importantly, during crawling, the microrobot's wings are retracted against its body, which prevents potential damage and enhances movement in tight spaces. Upon locating an optimal takeoff point, the robot can seamlessly extend its wings to revert to flight mode.

Educational and Research Applications

• Phan highlighted that our flapping robot may aid biologists in exploring insect flight mechanics and can be used as a disguised surveillance device to study real insects in forests, where traditional drones are not feasible. The robot's safe, low-flapping frequency also makes it suitable for engineering studies and as a playful, educational tool for kids.

Future Enhancements and Studies

• Phan and his team have conducted initial performance assessments of their microrobot, achieving encouraging results, Future work will focus on refining the design and testing it across diverse real-world scenarios to validate its full potential.

• "Future research could reveal whether other small insects, like flies, employ similar passive mechanisms given their limited muscle resources," Phan noted. "Additionally, we plan to enhance our robot's agile flight capabilities and integrate ground locomotion features, such as perching and crawling, to better mimic its biological counterparts."

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