World's smallest untethered flying robot takes off

Imagine a flying robot so small it could perch on your fingernail—and then take off again, without any wires or batteries.

That’s exactly what a team at the University of California, Berkeley, has just made real. In a paper published in Science Advances, Fanping Sui, Wei Yue, Kamyar Behrouzi, Yuan Gao, Mark Mueller, and Liwei Lin unveiled the world’s smallest and lightest untethered, controllable flying robot: a 21-milligram, 9.4-millimeter-wide, rotating-wing machine powered entirely by a magnetic field.

And it can do more than just lift off! It can hover, turn, survive collisions, and even recover its balance mid-air.

Shrinking flight to insect scale

Miniaturizing a flying robot is harder than it sounds. As you make it smaller, every gram matters, and carrying onboard batteries or motors quickly becomes impossible. Many insect-sized robots today stay “tethered,” drawing power through thin wires. This limits their movement and makes real-world exploration impossible.

The Berkeley team sidestepped this by using a single-axis alternating magnetic field as an invisible power cord. Tiny permanent magnets embedded in the robot’s body try to align with the field, creating torque that spins a four-blade propeller. This generates lift without any onboard power source.

To keep the robot stable, the engineers added a balance ring. This boosts rotational inertia, creating a gyroscopic effect—think spinning top—that helps it maintain its upright position in the air.

What it can do

In tests, the robot took off, hovered, adjusted its course, and survived mid-air bumps.

• Ascend with stability – Climbing at about 1.4 meters per second² while keeping its pitch angle within a degree or two of vertical.
• Hover briefly – By fine-tuning the magnetic field frequency to just under the lift-off threshold, it could hang in mid-air for almost half a second—an impressive feat at this scale.
• Recover after impacts – In more than three-quarters of collision tests, it stabilized itself and continued flying instead of crashing.
• Turn mid-flight – By introducing a magnetic field gradient, the team steered the robot left or right, no onboard sensors required.

All of this happens without cameras, sensors, or complex feedback loops! The stability comes from physics, not software.

How it stacks up

For perspective, the smallest untethered flying robot before this was about 28 mm wide. That is three times larger than Berkeley’s creation. At just 21 mg, it’s lighter than a grain of rice and far below the 1-gram mark that only three untethered robots have ever crossed.

Its lift-to-power ratio is among the highest in its class, 0.072 newtons per watt, beating most other designs, thanks to the absence of heavy onboard power storage and an efficient aerodynamic shape.

This isn’t just about breaking size records. Subcentimeter flying robots like UC Berkeley’s 21-milligram prototype could open doors to tasks that are currently impractical or impossible for larger drones. In medicine, they could navigate inside the human body to perform minimally invasive diagnostics or deliver targeted treatments. In industry, they could slip through narrow pipes, turbines, or other confined mechanical spaces to inspect for damage without the need for costly disassembly. In disaster zones, their tiny size would let them weave through rubble to locate trapped survivors. And in environmental science, they could quietly monitor insects, pollination, or microclimates without disturbing the natural balance. By combining their small size, wireless power system, and controllable flight, these robots could operate in environments that demand both delicacy and precision.

The big picture

Nature still holds the crown in the tiny-flight arena: a parasitic wasp called Nasonia vitripennis has a 3-millimeter wingspan and weighs just 0.58 mg. But inch by inch (or rather, millimeter by millimeter), robotics is catching up.

What makes this breakthrough exciting isn’t only the engineering elegance, but the fact that it opens a path to useful, autonomous, insect-scale robots, without the bulk and complexity of conventional drones.

Sometimes, moving forward in technology means thinking small. In this case, very small. And in that space between biology and engineering, the future of flight might just be the size of a sesame seed.

If you want to learn more, the original article titled "Untethered subcentimeter flying robots" is available on Science Advances at https://doi.org/10.1126/sciadv.ads6858