One of the world’s largest and strongest beetles might not seem like the best inspiration for a delicate flying microbot.
But using slow-motion cameras to capture creatures in flight, an international team has designed a flying micromachine that can expand and contract its wings. Similar to a rocket before takeoff and a flying insect after it’s in the air, the robot opens its wings when it takes off, then hovers and flaps effortlessly to stay in the air. When it lands, it retracts its wings back into its body.
The robot was inspired by the rhinoceros beetle, named for the distinctive horn that protrudes from the male’s forehead. The insect can grow up to 6 inches long—think Subway sandwiches of similar size. It can carry up to 100 times its own weight, earning it the nickname the Hercules beetle.
They are not stationary, muscular creatures. Covered in shiny black or gray exoskeletons, these beetles can fly up to two miles a day. But it is their sophisticated wing-laying system that has caught the eye of roboticists.
“Birds, bats, and many insects can fly by folding their wings against their bodies when at rest,” the authors wrote. But we didn’t know how the process worked in beetles.
It’s not just a scientific curiosity. The research could lead to the design of fluttering robots for search and rescue operations or environmental, agricultural and military monitoring.
The team explained that their findings could lead to improved designs for flapping-wing robots, particularly small robots with limited takeoff masses, which could “be able to open and close their wings more similarly to their biological counterparts.”
Annoyance with the concept
When it comes to creating minibots, nature is a source of creative inspiration.
In 1989, two intrepid scientists at MIT’s Artificial Intelligence Lab conceived and built a multi-legged robot to explore our planet and the solar system beyond.
Fast forward to early this year, and that idea is becoming a reality. A team has developed crawling minibug robots and artificial water sprays that mimic the movements observed in their natural counterparts. These are some of the smallest, lightest, and fastest fully functional robots ever, and they are helped to move by tiny motors called actuators.
Meanwhile, bees have inspired microbots that can fly even with damaged wings, and flies have inspired tiny accelerometers that sense wind and help control flight. Dr. Sawyer Buckminster Fuller of the University of Washington, who wrote the latter study, explained at the time why bugbots make sense: “First, they’re so small that they’re essentially safe around people. If a bug robot were to crash into you, it wouldn’t hurt. Second, they’re so small that they use very little power.”
However, these systems still require electricity or motors to control wing positions during takeoff, flight, and landing, limiting their range and usability. New research has found an alternative in beetles, an alternative that doesn’t require motors to extend and retract the bugbot’s wings.
Beetle Juice
The rhinoceros beetle was a dangerous inspiration. With two pairs of wings, each with its own mechanics and purpose, the beetle has always been difficult to study.
“Beetles have one of the most complex mechanisms of any insect species,” the authors wrote.
Some of this is due to the complex dynamics between the wing pairs. The forewings, also called elytra, are hard and shell-like. The hindwings, on the other hand, are delicate and membrane-like structures, think of the wings of a dragonfly. They fold in on themselves like an origami.
This, the team wrote, “allows it to be neatly stored between the body and the elytra when not in flight.”
The shell-like elytra protect the hindwing teammates when resting and spread out like fighter wings during flight. The hindwings spread and flap during flight and then fold back up when landing. Previous studies have suggested that muscles, elastic tissue, or other elements move the hindwings. In this study, the research team settled the debate by using high-speed cameras to record the beetle taking flight.
Wingman
The beetle’s wings spread in two steps.
First, like a fighter jet, the beetle spreads its hard-shelled wings. The hind wings extend slightly, using stored energy rather than muscle energy, through a spring-like mechanism. In other words, the beetle does not flex its muscles. The hind wings unfold naturally.
“This provides enough headroom for the subsequent flapping motion,” the team wrote.
The second stage activates synchronized flaps on both pairs of wings. The hind wings spread and assume a flying position, allowing the beetle to maneuver around corners.
These two work together to land. The elytra fold their hind wings into a neat resting position. The hard shell of the elytra protects them from above.
fluttering flying robot
The research team designed a flapping robot that mimics the wing system of a beetle.
It looks like a cyborg fly, with two translucent wings connected to a golden body and round head. Unlike beetles, bugbots only have one pair of folding wings that fold in on themselves when at rest, reducing their length by more than 60%.
Each wing is made of lightweight carbon and a flexible membrane. Combined with flexible joints, the bugbot rotates easily when flapping. Elastic tendons in the bot’s “armpits” can pull the wings back in just 100 milliseconds—the blink of an eye. The team used a single motor based on the elytra to spread the wings.
Upon activation, the wings quickly unfolded, lifting the minibot into the sky with two wing flaps. In a series of tests, the bot successfully took off, hovered, and landed. The wings automatically unfolded into flight position, generating the lift needed for takeoff. There was some wobbling while in the air, but it hovered and remained upright. Upon landing, the bugbot folded itself back up, folding its wings in the blink of an eye.
These folding wings have the added advantage of being flexible.
If the bugbot hits an obstacle and falls irreversibly, potentially crashing, it immediately folds its wings to protect itself from the impact. No muscle energy or other external control is required. This resilience could be useful when navigating dangerous terrain, such as after an environmental disaster.
Although this study focused on beetles, similar strategies could be used to observe and exploit the biological benefits of other insects, such as ladybugs.
“These experiments demonstrate new design principles for robust flight of flapping-wing microrobots under strict weight constraints in cluttered and confined spaces,” the team wrote.
Image credit: Hoang-Vu Phan
