Imagine tiny robotic bees buzzing around fields of wildflowers, helping real bees carry out their crucial pollinating duties decades in the future. It’s a vision that Harvard’s Microrobotics Laboratory has been working on for years. The barrier? Until recently, the only landing the Harvard RoboBee had mastered was a crash landing.
Harvard researchers have now armed their tiny RoboBee with four long, graceful landing appendages inspired by crane fly legs. (Crane flies are those nightmarish but harmless insects that look like flying spiders and people commonly misidentify as giant mosquitos). As detailed in a study published Wednesday in the journal Science Robotics, a soft landing brings RoboBees one step closer to practical applications that today would seem straight out of a sci-fi movie, such as environmental monitoring, disaster surveillance, artificial pollination, or even the manipulation of delicate organisms.
“Previously, if we were to go in for a landing, we’d turn off the vehicle a little bit above the ground and just drop it, and pray that it will land upright and safely,” Christian Chan, a PhD student at Harvard University’s School of Engineering and Applied Sciences and co-author of the study, explained in a Harvard statement.
Led by Robert Wood, a Harvard professor of engineering and applied sciences, Chan and his colleagues looked for inspiration for a new landing design within the university’s Museum of Comparative Zoology database. They ultimately chose the crane fly’s morphology, outfitting the RoboBee with four long, jointed legs for a softer landing. The update also included an improved controller (the robot’s brain) to decelerate the tiny robot’s landing approach. The combination now results in a “gentle plop-down,” as described in the statement.
Earlier versions of the RoboBee struggled to make a controlled landing because the air vortices generated from its flapping wings created instability close to the ground. It’s a problem appropriately called “ground effect” that helicopters also experience. Except it’s potentially more challenging for the RoboBee as it weighs 0.004 ounces (1/10th of a gram), and its wingspan measures just 1.2 inches (3 centimeters).
“The successful landing of any flying vehicle relies on minimizing the velocity as it approaches the surface before impact and dissipating energy quickly after the impact,” explained Nak-seung Patrick Hyun, a former Harvard postdoctoral fellow and now an assistant professor at Purdue University’s School of Electrical and Computer Engineering. “Even with the tiny wing flaps of RoboBee, the ground effect is non-negligible when flying close to the surface, and things can get worse after the impact as it bounces and tumbles.” Hyun led the RoboBee’s landing tests on both solid surfaces and a leaf, just like a real insect.
The crane fly legs and updated controller also protect the RoboBee’s fragile piezoelectric actuators—the tiny robot’s equivalent of an insect’s muscles. “The primary drawbacks of piezoelectric actuators for microrobots are their fragility and low fracture toughness,” the researchers explained in the study. “Compliant legs aid in protecting the delicate piezoelectric actuators from collision-induced fractures during crash landings.”
Moving forward, the team aims to give the RoboBee sensor, power, and control autonomy—what the statement calls “a three-pronged holy grail” that will bring its seemingly elusive practical applications that much closer to reality.
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