Engineers at the Harvard Microrobotics Laboratory have equipped the RoboBee with new landing gear inspired by the graceful landings of crane flies. This marks a significant engineering advancement for the tiny robot. The Harvard RoboBee, renowned for its ability to fly, dive, and hover like a natural insect, now has a more reliable way to land. The study was published in Science Robotics.
A composite image of the Harvard RoboBee landing on a leaf. Image Credit: John A. Paulson School of Engineering and Applied Sciences (SEAS)
The team led by Robert Wood, the Harry Lewis and Marlyn McGrath Professor of Engineering and Applied Sciences at the John A. Paulson School of Engineering and Applied Sciences (SEAS), has given their flying robot long, jointed legs to cushion its descent from air to ground. The robot also features an improved controller that helps it slow down as it approaches a landing, resulting in a gentle touchdown.
These enhancements are crucial for protecting the robot's fragile piezoelectric actuators – energy-dense "muscles" essential for flight that are easily damaged by the forces of rough landings and collisions.
Landing has historically been challenging for the RoboBee due to its minute size and weight – a mere tenth of a gram with a 3-cm wingspan. Earlier versions experienced significant ground effect, a destabilizing phenomenon caused by air currents generated by its flapping wings as it neared the ground, similar to the powerful downdraft produced by helicopter rotors.
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, Study Co-First Author, Lead and Graduate Student, John A. Paulson School of Engineering and Applied Sciences (SEAS)
The study details improvements to the robot's controller, or "brain," enabling it to adjust to the ground effect as it nears the surface. This effort was spearheaded by Nak-seung Patrick Hyun, a former postdoctoral researcher and co-first author. Hyun conducted controlled landing experiments on both leaf and rigid 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. 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.
Nak-seung Patrick Hyun, Former Postdoctoral Researcher, Study Co-First Author and Assistant Professor, Purdue University
The researchers drew inspiration from the natural world to enhance the crane fly's aerial agility and ability to land smoothly on diverse surfaces. They focused on the crane fly, a typically slow and harmless insect that appears from spring to autumn and is frequently misidentified as a large mosquito.
“The size and scale of our platform’s wingspan and body size was fairly similar to crane flies,” said Chan.
The scientists observed that crane flies possess long, jointed legs, which likely contribute to their ability to soften their landings. Additionally, crane flies are known for their short flights, spending a significant portion of their brief adult lives (ranging from days to a couple of weeks) transitioning between landing and takeoff.
Utilizing specimen records from Harvard's Museum of Comparative Zoology database, the team developed prototypes of various leg designs. They ultimately settled on configurations that closely resembled the leg segmentation and joint placement of crane flies. The lab employed advanced manufacturing techniques, pioneered within the Harvard Microrobotics Lab, to fine-tune the stiffness and damping characteristics of each joint.
Postdoctoral researcher and co-author Alyssa Hernandez, with her expertise in insect locomotion gained during her Ph.D. studies in Harvard’s Department of Organismic and Evolutionary Biology, provided valuable biological insights to the project.
“RoboBee is an excellent platform to explore the interface of biology and robotics, 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,” said Hernandez.
Currently, the RoboBee remains connected to external control systems. The team's ongoing efforts will increase the robot's size and integrate onboard electronics. This will provide the robot with its own sensing capabilities, power source, and control system. This crucial trifecta would enable the RoboBee platform to achieve true autonomy and operate independently.
“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. The safety tethers were, unsurprisingly, getting in the way of our experiments, and so safe landing is one critical step to remove those tethers,” said Wood.
The RoboBee's small size and impressive insect-like flying abilities suggest exciting potential uses in the future, such as monitoring the environment and surveying disaster areas. One particularly appealing application for Chan is artificial pollination, envisioning groups of RoboBees flying around vertical farms and future gardens.
This research received support from the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE 2140743.
RoboBee inspired by crane flies
Video Credit: John A. Paulson School of Engineering and Applied Sciences (SEAS)
Journal Reference:
Hyun, P. N., et al. (2025) Sticking the landing: Insect-inspired strategies for safely landing flapping-wing aerial microrobots. Science Robotics. doi.org/10.1126/scirobotics.adq3059