Passive wing deployment and retraction in beetles and flapping microrobots

Birds, bats and many insects can tuck their wings against their bodies at rest and deploy them to power flight. Whereas birds and bats use well-developed pectoral and wing muscles and tendons, how insects control these movements remains unclear, as mechanisms of wing deployment and retraction vary among insect species. Beetles (Coleoptera) display one of the most complex wing mechanisms. For example, in rhinoceros beetles, the wing deployment initiates by fully opening the elytra and partially releasing the hindwings from the abdomen. Subsequently, the beetle starts flapping, elevates the hindwings at the bases, and unfolds the wingtips in an origami-like fashion. Whilst the origami-like fold have been extensively explored, limited attention has been given to the hindwing base deployment and retraction, which are believed to be driven by thoracic muscles. Using high-speed cameras and robotic flapping-wing models, here we demonstrate that rhinoceros beetles can effortlessly elevate the hindwings to flight position without the need for 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 subsequent flapping motion that brings the hindwings into flight position. The results also show that after flight, beetles can leverage the elytra to push the hindwings back into the resting position, further strengthening the hypothesis of a passive deployment mechanism. Finally, we validate the hypothesis with a flapping microrobot that passively deploys its wings for stable controlled flight and retracts them neatly upon landing, which offers a simple yet effective approach to the design of insect-like flying micromachines.

Crash-perching on vertical poles with a hugging-wing robot

Perching with winged Unmanned Aerial Vehicles has often been solved by means of complex control or intricate appendages. Here, we present a simple yet novel method that relies on passive wing morphing for crash-landing on trees and other types of vertical poles. Inspired by the adaptability of animals' and bats' limbs in gripping and holding onto trees, we design dual-purpose wings that enable both aerial gliding and perching on poles. With an upturned nose design, the robot can passively reorient from horizontal flight to vertical upon a head-on crash with a pole, followed by hugging with its wings to perch. We characterize the performance of reorientation and perching in terms of impact speed and angle, pole material, and size. The robot robustly reorients at impact angles above 15{\deg} and speeds of 3 m/s to 9 m/s, and can hold onto various pole types larger than 28% of its wingspan in diameter. We demonstrate crash-perching on tree trunks with an overall success rate of 71%. The method opens up new possibilities for the use of aerial robots in applications such as inspection, maintenance, and biodiversity conservation.