For the first time a microrobotics lab developed an insect-size robot capable of flying and swimming. In 1939, a Russian engineer proposed a “flying submarine” — a vehicle that can seamlessly transition from air to water and back again. While it may sound like something out of a James Bond film, engineers have been trying to design functional aerial-aquatic vehicles for decades with little success. Now, engineers may be one step closer to the elusive flying submarine.
The biggest challenge is conflicting design requirements: aerial vehicles require large airfoils like wings or sails to generate lift while underwater vehicles need to minimize surface area to reduce drag. To solve this engineers at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS) took a clue from puffins. The birds with flamboyant beaks are one of nature’s most adept hybrid vehicles, employing similar flapping motions to propel themselves through air as through water.
“Through various theoretical, computational and experimental studies, we found that the mechanics of flapping propulsion are actually very similar in air and in water,” said Kevin Chen, a graduate student in the Harvard Microrobotics Lab at SEAS. “In both cases, the wing is moving back and forth. The only difference is the speed at which the wing flaps.” Coming from the Harvard Microrobotics Lab, this discovery can only mean one thing: swimming RoboBees.
For the first time, researchers at SEAS have demonstrated a flying, swimming, insect-like robot — paving the way for future dual aerial aquatic robotic vehicles. The research was presented recently in a paper at the International Conference on Intelligent Robots and Systems in Germany, where first author Chen accepted the award for best student paper.
The paper was co-authored by graduate student Farrell Helbling, postdoctoral fellows Nick Gravish and Kevin Ma, and Robert J. Wood, the Charles River Professor of Engineering and Applied Sciences at SEAS and Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering. The Harvard RoboBee, designed in Wood’s lab, is a microrobot, smaller than a paperclip, that flies and hovers like an insect, flapping its tiny, nearly invisible wings 120 times per second. In order to make the 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
“Bioinspired 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 recreate some of the features of organisms of interest.” This research was funded by the National Science Foundation and the Wyss Institute for Biologically Inspired Engineering.