By Soham NandiReviewed by Lily Ramsey, LLMApr 8 2025In a study published in Science Advances, researchers unveiled a 21-milligram (mg), 9.4-millimeter (mm) wingspan, magnetically powered flying robot—the smallest and lightest untethered aerial robot to achieve controlled flight, including hovering and collision recovery.
With a lift-to-drag ratio of 0.7, the robot operates efficiently even at low Reynolds numbers. The study offers key insights into wireless actuation, flight dynamics, and system design, advancing the field of subcentimeter-scale robotics.
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Background
Miniaturized aerial robots have long posed engineering challenges, particularly in power supply, propulsion, and aerodynamic performance at small scales. Many earlier designs depended on tethered systems to offload the power source, limiting maneuverability in real-world environments.
Recent developments have enabled untethered flight in centimeter-scale robots using external energy inputs such as light, wind, or electromagnetic fields. While magnetic actuation has previously been applied in micro-swimmers and ground-based robots, stable, untethered aerial flight using this method has yet to be achieved—until now.
Another major hurdle in microrobotics has been flight stability. Most small-scale robots lack onboard attitude control systems, which are typically too heavy or complex for subcentimeter designs.
This research addresses that limitation with a magnetically actuated 9.4-mm robot that combines stable flight, precise control, and power efficiency—without relying on onboard electronics.
By harnessing magnetic torque and a carefully balanced rotor design, the robot achieves controlled, untethered flight that includes hovering and recovery from collisions. This marks a significant step forward in realizing agile, wireless aerial robotics at insect-like scales.
Fabrication and Force Characterization
The robot’s lightweight frame was created using a Form 3 3D printer, with a resolution of 25 micrometers (μm) in the X-Y plane and a layer thickness of 50–100 μm.
The team used White V4 or Clear V4 resin to construct the frame, integrating two neodymium iron boron (NdFeB) permanent magnets (1 mm diameter, 0.5 mm length) into pre-designed notches that were 10% wider than the magnets. The magnets self-aligned via magnetic attraction, simplifying the assembly process.
To measure aerodynamic forces during flight, the researchers developed a custom lever-based force measurement system.
Fabricated with a Markforged X7 printer (50 μm resolution, carbon fiber-reinforced), the setup included shielded ball bearings and a high-precision force sensor (0.01 milli-newton resolution) salvaged from an analytical balance—allowing accurate lift measurements during testing.
Flight Performance and Maneuverability
Powered by a 340 hertz (Hz) alternating magnetic field, the robot achieved vertical flight while maintaining a pitch deviation of less than 5°. It generated 14% more lift than its body weight, allowing it to accelerate upward at 1.4 meters per second-squared (m/s²). With a lift-to-drag ratio of 0.7, the robot demonstrated both efficiency and control.
Hovering and recovery from mid-air collisions were key features. The robot recovered from 76.5% of impact events and pitch deviations up to 23°. A balance ring integrated into the design helped maintain stability through gyroscopic effects, reducing the impact of disturbances.
Adjusting the magnetic field gradient enabled lateral maneuvers, such as turning. For example, modulating the gradient enabled a left turn with a horizontal acceleration of 4.5 m/s². In terms of energy efficiency, the robot outperformed most existing micro flyers with a lift-to-power ratio of 0.072 newtons per watt (N/W).
Compared to earlier untethered aerial robots—which often exceed 100 mg in mass—this prototype marks a dramatic reduction in size and weight. While still heavier than the smallest natural fliers (e.g., a 0.58 mg wasp), it narrows the gap between robotic and insect-scale flight through a combination of magnetic actuation and aerodynamically optimized design.
Conclusion
This research presents the first untethered subcentimeter flying robot (9.4 mm, 21 mg) powered by an external magnetic field and capable of controlled flight, hovering, and collision recovery.
By combining lightweight 3D-printed structures with wireless magnetic actuation, the team overcame longstanding challenges in power delivery and stability at miniature scales.
The robot’s gyroscopic stabilization and field gradient-based steering allow agile, untethered movement without any onboard electronics.
While still heavier than the lightest natural insects, this breakthrough significantly advances the development of functional microrobots—bringing us closer to practical applications in environmental monitoring, medical diagnostics, and swarm robotics.
Journal Reference
Sui, F., Yue, W., Kamyar Behrouzi, Gao, Y., Mueller, M., & Lin, L. (2025). Untethered subcentimeter flying robots. Science Advances, 11(13). doi:10.1126/sciadv.ads6858. https://www.science.org/doi/10.1126/sciadv.ads6858
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