The RoboBee is a miniature robot that has long been able to fly. But what if the RoboBee lands in water? Using a modified flapping technique, researchers at the Harvard John Paulson School and Wyss Institute have demonstrate that the RoboBee can also swim. This is the first-ever aerial and aquatic capable insect-scale robot.
The Harvard RoboBee, designed in Wood’s lab, is a microrobot, smaller than a paper clip, that flies and hovers like an insect, flapping its tiny, nearly invisible wings 120 times per second. In order to make the RoboBee’s transition from air to water, the team first had to solve the problem of surface tension. The RoboBee is so small and lightweight that it cannot break the surface tension of the water. To overcome this hurdle, the RoboBee hovers over the water at an angle, momentarily switches off its wings, and crashes unceremoniously into the water in order to sink.
Next the team had to account for water’s increased density.
“Water is almost 1,000 times denser than air and would snap the wing off the RoboBee if we didn’t adjust its flapping speed,” said Helbling, the paper’s second author.
The team lowered the wing speed from 120 flaps per second to nine but kept the flapping mechanisms and hinge design the same. A swimming RoboBee changes its direction by adjusting the stroke angle of the wings, the same way it does in air. Like a flying version, it is still tethered to a power source. The team prevented the RoboBee from shorting out by using deionized water and coating the electrical connections with glue.
While this RoboBee can move seamlessly from air to water, it cannot yet transition from water to air because it can’t generate enough lift without snapping one of its wings. Solving that design challenge is the next phase of the research, according to Chen.
“What is really exciting about this research is that our analysis of flapping-wing locomotion is not limited to insect-scaled vehicles,” said Chen. “From millimeter-scaled insects to meter-scaled fishes and birds, flapping locomotion spans a range of sizes. This strategy has the potential to be adapted to larger aerial-aquatic robotic designs.”
“Bio-inspired robots, such as the RoboBee, are invaluable tools for a host of interesting experiments — in this case on the fluid mechanics of flapping foils in different fluids,” said Wood. “This is all enabled by the ability to construct complex devices that faithfully re-create some of the features of organisms of interest.”