One of the biggest and strongest bugs in the world hardly seems like the best inspiration for a gentle flying microbot.
But using slow-motion cameras to capture the critters in flight, an international team has designed a flying micromachine that can similarly extend and retract its wings. The robot — resembling a rocket before takeoff and a flying insect once airborne — deploys its wings for takeoff, then hovers easily and flaps them to stay aloft. After landing, it retracts its wings back into its body.
The robot was inspired by rhinoceros beetles, which were named after the distinctive horns protruding from the males’ foreheads. These critters can grow up to six inches long — think a similarly sized Subway sandwich — and carry up to 100 times their body weight in cargo, earning them the nickname Hercules beetles.
They are hardly stationary beefcakes. Covered in a shiny black or gray exoskeleton, these beetles can fly two miles a day. But it was their sophisticated wing deployment system that caught the attention of roboticists.
“Birds, bats and many insects can safely tuck their wings into their bodies and deploy them for flight,” but we didn’t know how the process worked in a beetle, the authors wrote.
It’s not just scientific curiosity. The research could lead to robot designs for search and rescue operations or environmental, agricultural and military monitoring.
The findings could improve the design of flapping-wing robots, especially smaller ones with limited take-off weight, the team explained, and “allow them to deploy and retract their wings much like their biological counterparts.”
A nuisance to imagine
When it comes to making minibots, Mother Nature is a source of creative inspiration.
In 1989, a pair of intrepid scientists at MIT’s Artificial Intelligence Lab envisioned and built several small, multi-legged robots to explore our planet and the solar system beyond.
Fast forward to the beginning of this year and the idea is becoming a reality. One team developed a crawling MiniBug robot and an artificial water pedal by mimicking the movements seen in their natural counterparts. These were some of the smallest, lightest and fastest fully functional robots yet, relying on small motors – called actuators – to help them move.
Meanwhile, bees have inspired microbots that fly, even with damaged wings, and flies have inspired tiny accelerometers that sense wind and aid in flight control. Dr. Sawyer Buckminster Fuller of the University of Washington, an author of the second study, explained at the time why bugbots make sense. “First of all, they are so small that they are inherently safe among humans. If an insect robot crashes into you, you won’t get hurt. The second is that they are so small that they use very little power.’
Yet these systems still require electricity or motors to control the position of the wings during takeoff, flight and landing, limiting their range and usefulness. A new study looked to beetles for an alternative—one that doesn’t require motors to extend and retract the beetle’s wings.
Beetle Juice
The rhinoceros was a risky inspiration. With two pairs of wings—each with its own set of mechanics and uses—the beetle has always been difficult to study.
“Beetles … have one of the most complex mechanisms among different insect species,” the authors wrote.
This is partly due to the complex dynamics between the wing pairs. The front wings, also called elytra, are hardened and shell-like. The hindwings, on the other hand, are delicate, membranous structures—think dragonfly wings—that fold together like origami.
This “allows them to nestle neatly between the body and the elytra” when not in flight, the team wrote.
The shell-like elytra protect their mates on the hindwings at rest and spread out like the wings of a fighter jet in flight. The hind wings unfurl and flap during flight, then fold back upon landing. Previous studies have suggested that muscles, stretching tissues, or other elements power the hindwings. Here, the team put the debate to rest by using high-speed cameras to record the bugs in flight.
Partner
The beetle’s wings spread in two steps.
First, as a fighter, the beetle puts on a hard-shelled elytra. Through a spring mechanism, the rear wings are then stretched slightly using stored energy rather than muscle energy. In other words, the beetle does not stretch its muscles – its hind wings naturally expand.
“This allows for the clearance needed for the subsequent flapping motion,” the team wrote.
The second stage activates the synchronized flaps of both wing pairs. The hind wings unfurl and assume a flight position, allowing the beetle to maneuver through nooks and crannies.
The duo also worked in concert to land. The elytra push the hindwings to fold and tuck neatly into a resting position – protected from above by the hard shell of the elytra.
Waving flying boots
The team designed a flapping robot that mimics the wing system of beetles.
It looks like a cyborg fly with two translucent wings attached to a golden body and a round head. Unlike the beetle, the bugbot has only one pair of retractable wings that fold into themselves when at rest, reducing its length by more than 60 percent.
Each wing is made of lightweight carbon and a flexible membrane. Combined with flexible joints, the bugbot turns easily as it moves. An elastic tendon in the robot’s “armpit” can pull the wings back in just 100 milliseconds – or in the blink of an eye. The team used a single elytra-based engine to deploy them.
Once activated, the wings quickly spread, propelling the minibot skywards in two flaps. In a series of tests, the robot successfully took off, hovered and landed. The wings will automatically deploy to flight position and create enough lift for take off. While in the air, it hovered and remained upright, despite some wobbles. Upon landing, the bugbot folded into itself and retracted its wings in the blink of an eye.
These retractable wings have another advantage – durability.
If the bugbot hits an obstacle, causing it to flip over irretrievably and potentially crash, it immediately retracts its wings to protect it from the impact – without the need for muscle power or other external controls. This resilience can come in handy when navigating dangerous terrain – such as after an environmental disaster.
Although the study focused on rhinoceroses, a similar strategy could be used to observe and exploit biological benefits from other insects such as ladybugs.
“These experiments … (demonstrate) a new design principle for robust flapping-wing microrobot flight with severe weight constraints in confined and confined spaces,” the team wrote.
Image credit: Hoang-Vu Phan