A flapping robot swims and flies like a diving bird

Engineers at EPFL and MIT have created a flapping-wing aerial-aquatic vehicle, or FAAV, that can swim underwater, rise through the surface, and continue flying in air. Inspired by diving birds such as loons, gulls, puffins, and petrels, the robot is intended both to study how birds move across water and air and to suggest a new type of drone for aquatic research.

The vehicle weighs under 300 grams and consists of a fuselage, two flexible flapping wings, and a steerable, motorized tail. Its interchangeable wings and tail allow different sizes to be tested. Thin membrane wings are coated with hydrophobic nanoparticles to shed water. A battery and waterproof electric motor drive a crankshaft that moves the wings at preset frequencies, while the tail changes angle to control ascent and descent.

Tests in an EPFL water tank and Lake Geneva examined wing dimensions, flexibility, flapping frequency, and tail angle. Researchers found that 80-centimeter wings with suitable flexibility were important: they had to reduce flapping amplitude underwater while remaining stiff enough for flight. At about five flaps per second, the robot swam at nearly one meter per second and flew at roughly six meters per second, values described as similar to diving birds. A pitch of about 70 degrees was needed for water-to-air takeoff so the wingtips avoided the surface.

Unlike many diving birds, which paddle with their feet when taking off, the robot achieved the transition using wings without feet. The team plans to develop wings that can turn as well as flap, evaluate operation in choppy water and wind, and eventually explore uses such as collecting measurements or samples in difficult-to-reach aquatic areas.