A new ultra-lightweight robot can swim underwater before emerging to fly through the air like a bird. The flapping-wing aerial-aquatic vehicle (FAAV), developed by researchers at EPFL in Switzerland and the Massachusetts Institute of Technology (MIT), takes inspiration from diving birds such as puffins, gulls, loons and petrels that can both fly and swim.
Design and Testing
The study, published in the journal Science, examined how a lightweight robot weighing less than 300 grams could replicate the movements of birds that dive beneath the water's surface and return to the air. The robot features a central fuselage, two flexible flapping wings and a steerable tail. Its wings are made from thin membranes coated with hydrophobic nanoparticles to repel water, while a waterproof electric motor drives the flapping motion.
During tests in a laboratory water tank and later in Lake Geneva, the team identified combinations of wing size, flapping frequency and tail angle that enabled the robot to swim underwater, break through the surface and continue flying. Researchers found that wings measuring around 80 centimetres across provided the best balance between flexibility in water and rigidity in flight.
Performance and Transition
The robot achieved a swimming speed of almost one metre per second while flapping its wings around five times a second, then flew at approximately six metres per second using a similar wingbeat frequency. To transition from water to air, the robot had to pitch upwards at an angle of about 70 degrees to prevent its wingtips from touching the surface.
Lead author Raphael Zufferey, a former EPFL researcher now an assistant professor of mechanical engineering at MIT, said the technology could be used for environmental monitoring. 'Our dream vision is for oceanographers, marine biologists and 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, a port facility or over a pod of whales,' he said. '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.'
Unique Capabilities
Unlike many diving birds, the robot does not require feet to launch itself from the water. 'If you look at birds, most birds need to paddle their feet at the surface to take off. And the question was, do we need the same for robots? And it turns out we don't,' Zufferey said. 'No one's been able to fly out of the water with wings.'
Future Developments
The research team is now working on improving the wing design so that the robot can also rotate its wings while flying. Future tests will examine how it performs in rough water and windy conditions before it is deployed in ocean research.
