Flying robot uses beetle’s unique mechanism for takeoff, mid-air stability

The rhinoceros beetle possesses a unique capability, it passively deploys and retracts hindwings without using muscle.

Taking inspiration from it, an international team of researchers has created a flapping microrobot that shows that passive wing deployment can work for stable and controlled flight.

The team used slow-motion cameras to capture the insects in flight to develop a system that similarly expands and retracts its wings.

The study revealed that beetles use elastic energy and flapping forces to passively deploy hindwings for flight and retract them using the elytra (modified, hardened forewing of beetles) rather than relying on specific thoracic muscles.

The team applied this principle to flapping-wing microrobots, demonstrating passive wing deployment for takeoff, stable hovering, and rapid retraction upon landing or collisions.

According to the team, the research offers insights into insect locomotion and micro-scale robot design.

Insect wing folding mystery

Flying insects’ wings are fragile yet essential for activities like evading predators, foraging, migrating, and mating.

To protect these vital structures, many insects can fold their wings against their bodies, minimizing damage risks and interference during ground movement.

Beetles, possessing both hardened forewings (elytra) and delicate hindwings, exhibit a particularly complex wing mechanism.

While previous studies suggest muscles drive the unfolding and folding of these wings, no experimental evidence supports muscle involvement in hindwing deployment and retraction.

To understand how a beetle elevates its hindwings, researchers used synchronized high-speed cameras to record the wing deployment kinematics of the rhinoceros beetle Allomyrina dichotoma.

The beetle initiates a two-phase wing deployment during flapping flight. In the first phase, the elytra are fully elevated, followed by a partial release of the hindwings to about 48.5° from the abdomen , while the wingtips remain folded. This release appears to be triggered by stored elastic energy rather than muscle activity.

The second phase begins with synchronized flapping of both wing pairs, elevating the hindwing bases, and unfolding the wingtips into the flight position. This sequence occurs independently of the initial elevation.

The team hypothesizes that flapping forces, particularly centrifugal force, contribute to the passive elevation of the hindwings.

Insect-inspired robot flight

To validate the passive wing deployment and retraction mechanism, a flapping microrobot capable of mimicking beetle wing motion without active mechanisms was developed.

Unlike previous robots with fixed extended wings, this design incorporated an elastic tendon to facilitate wing folding and deployment, triggered by flapping motion.

Experiments showed that the centrifugal force generated during flapping was sufficient to elevate the wings despite minor deviations from the expected angle.

According to researchers, by adjusting the elevation threshold, the microrobot achieved stable flight forces comparable to those of non-retractable wing designs.

The robot’s wings could decrease their span from 20 cm to 3 cm when folded and deployed within two flapping cycles, retracting within 100 ms upon motor deactivation.

Testing included untethered takeoff, hovering, and landing, demonstrating the robot’s ability to maintain stable flight and retract wings when hitting obstacles.

Researchers say these findings support passive wing mechanisms and present a new design principle for flapping-wing microrobots in confined spaces.

The details of the team’s research were published in the journal Nature .