Néstor Pérez-Arancibia’s tiny robots can scuttle up inclines like beetles, circle in the air like bees, or glide through water like aquatic insects.
For decades, science fiction writers have pictured a world where robotic insects perform essential tasks. One of Isaac Asimov’s short stories even describes robotic bees.
“There are so many potential uses for robots inspired by insects,” says Pérez-Arancibia, an associate professor and director of Washington State University’s Autonomous Microrobotic Systems Laboratory. “They could pollinate crops. They could locate people trapped in buildings after earthquakes or other natural disasters. They could collect monitoring data from contaminated areas. They could explore caves.”
But building microrobots that crawl, fly, or swim comes with steep challenges. Scientists have long struggled not only to imitate insects’ movements but to find an energy source as powerful as their body fat.
Even the best batteries can’t compare with animal fat in terms of energy density, Pérez-Arancibia says. By volume, the battery would need to be about 30 times larger than the corresponding unit of fat.
Pérez-Arancibia and two of his former doctoral students at the University of Southern California made breakthroughs in both areas with the 2020 rollout of the RoBeetle, which was listed in Guinness World Records as the smallest liquid-fueled robot.
“We beat the next autonomous robot by a factor of 10 in terms of weight,” says Pérez-Arancibia, who continues to refine the RoBeetle at WSU.
At 88 milligrams, the RoBeetle weighs about as much as three grains of rice. Besides climbing inclines, it can haul loads up to 2.6 times its own weight, and walk for two hours without stopping. At top speed, the RoBeetle travels at about 4.5 centimeters per minute.
Methanol fuels the RoBeetle, and its artificial muscles are made with shape-memory alloys—metal alloys that change shape during heating and cooling. A fuel tank on the microrobot’s body releases methanol through a vent, causing a reaction with a shape-memory alloy wire that mechanically moves the RoBeetle’s legs.
In Pérez-Arancibia’s lab, doctoral students conceptualize and build robotic insects out of microcircuit boards, sensors, layers of carbon fiber, and other materials. They also work on controllers, the artificial brains that operate the robots.
Months of work go into designing and testing each new microrobot. The team is constantly challenging itself to improve efficiency and range of motion. Pérez-Arancibia’s most recent creation is the Bee++, a four-winged flying microrobot that weighs 95 milligrams.
Each of the Bee++’s wings are controlled by separate actuators, allowing the microrobot to fly in all directions and perform pitching, rolling, and twisting maneuvers. Powered by an onboard battery, its flight time is about five minutes. Tethered to an electrical source, it can remain in the air for an unlimited amount of time.
Wings that beat 160 times per second contribute to the Bee++’s flight stability and control. In addition, the team is working on a microrobot inspired by the aerodynamic efficiency of butterflies’ flight. Just like butterflies can fly for long periods, the design holds promise for achieving sustained autonomous flight, Pérez-Arancibia says.
He’s also developing two swimming microrobots, which could someday help with water-quality testing. The designs are loosely based on the movements of eels and water striders.
“We use some of the principles we see in nature, but we aren’t trying to replicate nature,” Pérez-Arancibia says.
The WaterStrider weighs 55 milligrams and can move at 6 millimeters per second.
(Photo Robert Hubner)
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