MIT and EPFL Develop Robot Capable of Flying, Diving, and Swimming

Engineering the Air-to-Water Transition

Engineers have found the natural ability of diving birds to move between air and water incredibly difficult to recreate at a small scale. While roughly 100 bird species—such as puffins, gulls, and petrels—naturally navigate these two environments, building a machine to do the same has proven difficult. Most amphibious robots rely on separate systems for air and water, like propellers for water and wings for air, or complex leg-based mechanisms to assist with takeoffs.

The new flapping-wing aerial-aquatic vehicle (FAAV) takes a simpler approach. By utilizing a single set of flexible wings, the robot manages the significant density difference between air and water—a ratio of about 800 to 1—without swapping hardware.

Flight Mechanics and Wing Flexibility

The key to the robot’s functionality lies in its wing design and flapping frequency. To handle the increased resistance of water, the wings are designed to be flexible; they can bend by as much as 90 percent, which reduces the load on the motor and shortens the effective sweep of each stroke. While the robot flaps its wings up to 11 times per second in the air, that rate drops to between 0.1 and 6 times per second while submerged.

The transition back to flight is the most complex phase of the maneuver. The robot completes this jump in under one second using approximately eight to 10 wingbeats.

• Launch Angle: An exit angle near 70 degrees is required to prevent the robot from tipping backward or dragging its tail.
• Wing Stiffness: The wings must be moderately flexible—firm enough to keep the robot aloft in the air but flexible enough to adapt to underwater pressure.
• Neutral Buoyancy: By ensuring the robot neither sinks nor rises on its own, researchers conserve battery power, avoiding the need to fight buoyancy during underwater transit.

Future Applications in Marine Research

Raphael Zufferey, an assistant professor of mechanical engineering at MIT who led the research, envisions the robot serving as a tool for oceanographers and marine biologists. By deploying these devices from boats or shorelines, scientists could monitor whales, sample water quality, or inspect infrastructure like port facilities at a fraction of the cost of traditional vessels.

“Our dream vision is for oceanographers, marine biologists, and members of coastal communities to launch this robot from a boat, or from shore, and it would fly close to the area of interest, such as an iceberg or a port facility, or over a pod of whales. It would dive into the water to take a measurement or collect a sample, and fly back to deliver the data at a fraction of the cost of traditional methods. Then it could go back out to dive for more.”

Raphael Zufferey, assistant professor of mechanical engineering at MIT

The project also provides a physical model for studying real-world avian behavior. The robot’s performance data suggests that diving birds may reduce their wingspan underwater to increase speed rather than simply to conserve energy, a theory that has been difficult to test on live animals.

Accessibility and Next Steps

With a material cost of around $300, the robot is designed to be replicable.

The findings were published in the journal Science.