Flapping Robot Mimics Diving Birds to Swim and Fly

Engineers at MIT and EPFL have built a bird-sized robot that can swim underwater and launch into flight using only its wings, inspired by diving birds like puffins.

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A new flapping-wing robot can swim underwater and then burst out of the water to fly through the air, a feat that has eluded previous robotic designs. The device, described in a paper published in Science, weighs about half a pound and has a wingspan of nearly three feet. It was developed by researchers at the Massachusetts Institute of Technology and the École Polytechnique Fédérale de Lausanne.

The robot's design draws inspiration from diving birds such as the Atlantic puffin, which use their wings for both swimming and flying. Lead author Raphael Zufferey, now an assistant professor at MIT, noted that the challenge is moving through air and water despite their vastly different densities. The team aimed to create a robot that could transition between the two mediums without the use of legs or foldable wings, which are common in diving birds but complex to implement in robotics.

Instead, the robot relies on flexible wings made of nylon fabric reinforced with carbon fiber struts. The wings flap five to six times per second during flight, but to launch from water, they must flap at ten times per second to generate enough speed and thrust. The robot's open body design allows water to flood its interior, making it neutrally buoyant, while each electronic component is individually waterproofed.

In tests conducted at Lake Geneva, the robot successfully leaped from the water into the air in less than a second. The researchers computed optimal launch angles and wing sizes, finding that a steep 70-degree pitch is necessary to prevent the wingtips from hitting the water's surface. On a single charge, the robot can fly for nearly four miles or swim for just over a mile.

Animal movement biologist Glenna Clifton from the University of Portland, who was not involved in the study, called the robot "a monumental step in the performance at both swimming, flying, and transitioning between the two." She highlighted that the robot offers insights into the flight biology of diving birds and has potential applications in coastal monitoring, such as observing coral reefs or algal blooms.

The ultimate vision, according to Zufferey, is for oceanographers and marine biologists to deploy the robot from a boat or shore to fly to areas of interest, dive for samples, and return with data at a fraction of traditional costs. The team plans to equip future versions with onboard sensors and improve wing design for turning and performance under turbulent conditions.