Researchers at MIT and EPFL have built a bird-scale, 300-gram robotic vehicle capable of swimming underwater, launching from the surface without legs, and transitioning directly into flapping flight. Described in the journal Science, the amphibious drone offers oceanographers a low-cost tool for marine research and provides biologists a new way to study diving seabirds.
Watching an Atlantic puffin or a kingfisher drop from the sky and vanish beneath the waves looks effortless. Translating that fluid agility into a machine, however, has frustrated engineers. Water is roughly 800 times denser than air, meaning wings designed for the sky face immense resistance the moment they submerge. Now, a joint research team from the Massachusetts Institute of Technology and the Swiss Federal Institute of Technology Lausanne has bridged that gap with a lightweight, flapping-wing aerial-aquatic vehicle.
Engineering a Flapping-Wing Amphibious Robot for Air and Water
The machine weighs less than 300 grams—or about 8.8 ounces—and spans under three feet from tip to tip. Its central fuselage houses an electric motor, battery, and exposed electronics, meaning water floods the internal structure entirely. To protect the hardware, engineers individually waterproofed every single electronic component. The wings are constructed from translucent nylon fabric reinforced with carbon fiber struts, and the outer surfaces feature a coating of water-repellent nanoparticles.
Unlike most amphibious robots that rely on propellers and separate propulsion systems for different environments, this mechanical bird relies exclusively on its wings. During tests in laboratory water tanks and Lake Geneva, the team found that interchangeable wings measuring about 80 centimeters across provided the ideal compromise: they stayed flexible enough to bend by up to 90 degrees under heavy water pressure, shortening the effective stroke and reducing motor load, yet remained rigid enough for flight once airborne.
How the Robot Masters the Transition from Water to Air
The hardest challenge in aerial-aquatic robotics is the moment of departure. When leaving the water, the vehicle must generate a massive burst of thrust in under one second. While heavier seabirds like ducks and puffins rely on their legs to run along the surface and gain takeoff speed, this lightweight robot launches entirely through wing power.
In the air, the machine flaps its wings roughly five to six times per second, matching the patterns of small diving birds. To punch out of the water, that frequency jumps to around 10 beats per second. According to the research team’s data, the exit maneuver requires a precise combination of wing flexibility, tail pitch, and a launch angle near 70 degrees. A flatter exit creates too much drag from the short tail, while a near-vertical launch causes the robot to tip backward.
Furthermore, the robot maintains neutral buoyancy while submerged, ensuring it neither sinks nor floats on its own. This balance helps conserve battery power by eliminating the energy required to fight water density.
Field Applications for Oceanographers and Marine Biologists
The creation of a bird-scale aquatic flyer opens up new possibilities for field research. Traditional vessels and underwater submersibles are expensive and struggle to access shallow reefs, choppy coastal zones, or icy polar margins. This drone offers an agile alternative at a fraction of the cost.
Once it arrives at a destination, the robot can dive into the water to take a measurement or collect a sample, then fly back to deliver the data before heading out again. Glenna Clifton, an animal movement biologist at the University of Portland who was not involved in the study, called the machine a beautiful, light, and powerful step forward that highlights the unique mechanics of natural flight.
New Insights Into the Physics of Natural Diving Birds
Beyond its utility as a field tool, the robot provides biologists with a controllable physical model to study real animals. Observing live seabirds beneath the surface is notoriously difficult, but engineers can adjust a single variable on the robot—such as wingspan or stroke length—to measure its precise effect on performance.
For instance, biologists have long debated why many diving birds shorten their wingspans while swimming.
Next Steps for Testing and Deployment
With the core mechanics established, the research team is turning its attention to maneuverability and environmental durability. Current development focuses on upgrading the wing design to allow rotational movement, giving the robot the ability to execute sharp turns in mid-air rather than just flapping vertically.
Researchers also plan to test how the vehicle performs under turbulent conditions, including swimming out of choppy waters and flying through strong winds. The platform could soon transform how coastal communities and scientific expeditions monitor fragile marine habitats.
Worth a look
