Envision a future where tiny robotic bees, known as RoboBees, flit about fields of wildflowers, collaborating with real bees to perform their vital pollinating duties. This is a vision that Harvard’s Microrobotics Laboratory has been tirelessly working towards for years. However, until recently, the only type of landing the Harvard RoboBee had mastered was the crash landing.

Researchers at Harvard have now equipped their miniature RoboBee with four lengthy, elegant landing appendages, drawing inspiration from the legs of crane flies. Crane flies are those intimidating yet harmless insects that resemble flying spiders and are often misidentified as giant mosquitoes. According to a study published on Wednesday in the journal Science Robotics, the RoboBee’s newfound ability to land softly brings it one step closer to realizing practical applications that seem like the stuff of science fiction, such as environmental monitoring, disaster surveillance, artificial pollination, and even the manipulation of delicate organisms.

“In the past, when attempting to land, we would shut off the vehicle slightly above the ground and simply drop it, hoping it would land upright and safely,” explained Christian Chan, a PhD student at Harvard University’s School of Engineering and Applied Sciences and co-author of the study, in a Harvard statement.

Under the guidance of Robert Wood, a Harvard professor of engineering and applied sciences, Chan and his colleagues sought inspiration for a novel landing design within the university’s Museum of Comparative Zoology database. Ultimately, they chose the crane fly’s morphology, outfitting the RoboBee with four long, jointed legs to achieve a softer landing. The update also included an improved controller, essentially 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 due to the air vortices generated by its flapping wings, which created instability close to the ground. This problem, known as “ground effect,” is also experienced by helicopters. However, it is potentially more challenging for the RoboBee, as it weighs a mere 0.004 ounces (1/10th of a gram) and has a wingspan of 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, mimicking the behavior of a real insect.

The crane fly legs and updated controller also serve to protect the RoboBee’s fragile piezoelectric actuators, which are 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.”

Looking ahead, the team aims to grant the RoboBee sensor, power, and control autonomy, referred to as “a three-pronged holy grail” in the statement, which will bring its seemingly elusive practical applications that much closer to reality.