Small drones need to stay aloft do their jobs — whether that’s searching for dangerous gas leaks or remotely monitoring atmospheric conditions. But this effort can quickly drain battery-powered energy.
A team of Harvard roboticists and a University of Washington mechanical engineer have demonstrated that their insect-sized flying robots, nicknamed the RoboBees, can now perch during flight to save energy — like bats, birds or butterflies.
In a paper published in Science on May 19, they describe a switchable electroadhesive that enables a flying robotic insect to perch on materials such glass, wood or a leaf. This requires roughly 1,000 times less power than sustained flight.
“One of the biggest difficulties with building insect-sized robots is that the physics change as you go that small. A lot of technologies that have been deployed successfully on larger robots become impractical on a centimeter-sized robot,” said co-author Sawyer Fuller, UW assistant professor of mechanical engineering. “We take inspiration from flying insects because they’ve already found solutions for these challenges.”
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A swarm of insect-sized flying robots equipped with sensors could collect detailed information about air pollution, Fuller said, including searching for methane leaks that are a significant source of greenhouse gas pollution. But that will require energy-saving solutions that extend current flight times.
“Many applications for small drones require them to stay in the air for extended periods,” said Moritz Graule, first author of the paper who conducted this research as a student at the Harvard John A. Paulson School of Engineering and Applied Sciences and Wyss Institute for Biologically Inspired Engineering. “Unfortunately, smaller drones run out of energy quickly. We want to keep them aloft longer without requiring too much additional energy.”
Mechanisms that animals use to perch, such as sticky adhesives or talons, aren’t easily adaptable to a paper clip-size microrobot. So the team turned to electrostatic adhesion — the same basic science that causes a static-charged sock to cling to a pants leg or a balloon to stick to a wall.
The RoboBee, pioneered at the Harvard Microrobotics Lab, uses an electrode patch and a foam mount that absorbs shock. The entire mechanism weighs 13.4 mg, bringing the total weight of the robot to about 100mg — similar to the weight of a real honeybee. The robot takes off and flies normally. When the electrode patch is supplied with a charge, it can stick to almost any surface, from glass to wood to a leaf. To detach, the power supply is simply switched off.
The patch requires about 1,000 times less power to perch than it does to hover, which can dramatically extend the operation life of the robot.
“When making robots the size of insects, simplicity and low power are always key constraints,” said Robert Wood, Charles River Professor of Engineering and Applied Sciences at SEAS and core faculty member of the the Wyss Institute, and senior author of the study.
Fuller, who led the RoboBees flight experiments as a postdoctoral scholar at Harvard, joined the UW Mechanical Engineering Department in 2015. He will continue his research as part of The Air Force Center of Excellence on Nature-Inspired Flight Technology and Ideas (NIFTI) housed at the UW.
“One of the things I’m focusing on is how we can start giving these insect-sized robots the ability to perceive the world and control their own flight,” Fuller said.
“Right now the robot relies on an external array of cameras and computers to fly,” he said. “That proves that we have the necessary fabrication technology in place, but we’d like to eliminate the external cameras. With sensors onboard, the robot will be able do things like stabilize its flight, locate suitable landing sites, or follow the source of an odor plume. “
The Science paper was coauthored by Pakpong Chirarattananon, Noah Jafferis, Matthew Spenko and Roy Kornbluh. The research was funded by the National Science Foundation, the Wyss Institute for Biologically Inspired Engineering, and the Swiss Study Foundation.