This breakthrough, reported in Science Robotics, marks a significant step forward for micro-aerial vehicles. The research team, led by Robert Wood, professor of engineering and applied sciences at Harvard's John A. Paulson School of Engineering and Applied Sciences, incorporated elongated jointed legs to ease RoboBee's descent and landing. An improved controller assists in decelerating the robot during final approach, significantly reducing impact force and protecting fragile components such as its piezoelectric actuators.

Weighing only a tenth of a gram with a 3-centimeter wingspan, RoboBee has long faced instability issues during landings due to air turbulence created by its flapping wings-a phenomenon known as ground effect. Previous strategies relied on cutting power mid-air and hoping for a stable fall. "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," said co-first author Christian Chan, who spearheaded the mechanical redesign.

New control algorithms now enable RoboBee to account for aerodynamic disturbances near surfaces. Co-first author Nak-seung Patrick Hyun, now a professor at Purdue University, led tests on various landing surfaces. "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," Hyun explained. Even at RoboBee's tiny scale, he added, ground effect remains a formidable challenge.

To refine the landing mechanism, researchers turned to the crane fly-a fragile insect with a build similar in scale to RoboBee. Known for their short, low-altitude flights and long, segmented limbs, crane flies provided a fitting model. The team used entomological data from Harvard's Museum of Comparative Zoology to design legs with biologically accurate stiffness and damping properties.

Postdoctoral researcher Alyssa Hernandez, who holds a Ph.D. in insect locomotion, emphasized the benefits of bioinspiration. "RoboBee is an excellent platform to explore the interface of biology and robotics," she said. "Seeking bioinspiration within the amazing diversity of insects offers us countless avenues to continue improving the robot. Reciprocally, we can use these robotic platforms as tools for biological research, producing studies that test biomechanical hypotheses."

Although the robot remains tethered to external control systems, the long-term vision includes untethered operation with onboard sensors, power supplies, and autonomous control. "The longer-term goal is full autonomy, but in the interim we have been working through challenges for electrical and mechanical components using tethered devices," said Wood. With improved landing reliability, removing the tether is now within closer reach.

Looking ahead, RoboBee's compact size and nimble flight could enable applications ranging from environmental monitoring to artificial pollination. "Picture swarms of RoboBees buzzing around vertical farms and gardens of the future," said Chan.

The project was supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE 2140743.

Research Report:Sticking the landing: Insect-inspired strategies for safely landing flapping-wing aerial microrobots

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