The rhinoceros beetle turns out to be an unlikely source of engineering inspiration for tiny flying robots that can fold their wings when resting or after a collision.

The insects deploy and retract their hindwings in a passive process that requires no muscular activity, providing a puzzle for researchers. While their hardened forewings - called elytra - are driven actively by their own muscles, little was known about how the bug deploys and retracts its delicate membranous hindwings. Researchers have proposed that muscles drive their movement, but little experimental evidence has been found to support the idea.

Beetles offer one of the most complex wing mechanisms among flying insects. For example, rhinoceros beetles open their wings by releasing the elytra simultaneously with a partial release of the hindwings at their bases. As the creature begins to flap, its hindwing bases rise and unfold like origami.

By analyzing high-speed film of flapping rhinoceros beetle and building a similar flying robot, Hoang-Vu Phan, a postdoctoral researcher at Switzerland's Ecole Polytechnique Fédérale de Lausanne (EPFL), set out to shed light on how the rhinoceros beetle powers the process.

In a paper published in Nature today, the authors said they had demonstrated that rhinoceros beetles can effortlessly deploy their hindwings without muscular activity. "We show that opening the elytra triggers a spring-like partial release of the hindwings from the body, allowing the clearance needed for the subsequent flapping motion that brings the hindwings into the flight position," they said.

The study also shows that after a flight concludes, the beetle can use its front wings to push the hindwings back into the resting position, which provides more evidence of their passive movement.

"We validated the hypothesis using a flapping microrobot that passively deployed its wings for stable, controlled flight and retracted them neatly upon landing, demonstrating a simple, yet effective, approach to the design of insect-like flying micromachines," the study said.

By using the same principles of passive deployment-retraction in a flapping-wing robot, the team showed they could deploy its wings for take-off, perform stable hovering, and rapidly retract the wings against the body upon landing or in case of in-flight collisions without the need for additional actuators.

"Our findings not only contribute to the understanding of locomotion strategies in insects but also have implications for flapping-wing robots, particularly those at small scales with limited take-off weights, enabling them to deploy and retract their wings similarly to their biological counterparts," the paper said.

The researchers are not the only team to take inspiration from the insect world for robot design. Other notable examples include a solar-powered, remote-controlled cyborg cockroach, indestructible robot cockroaches, and giant robot grasshoppers. ®

https://www.theregister.com//2024/08/01/rhino_beetle_robot_design/