Insect-like robots inspired by puffins that can switch from air to water have been created by American researchers.
The RoboBees, created by engineers at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS), are among the first robotic creatures that can effectively tackle water as well as air environments.
Although they are currently only able to switch from air to water and not back to air, the RoboBees present a successful solution for conflicting design requirements that have so far been hindering development of dual aerial-aquatic robots.
While aerial vehicles require large airfoils like wings or sails to generate lift, underwater vehicles need to minimise surface area to reduce drag.
To create the RoboBee, the engineers looked for inspiration in nature. They studied the motion of puffins, which are small seabirds recognisable by their typical orange beaks. Puffins can skilfully move through air and water using the flapping movements of their wings.
“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, who presented the RoboBee at the International Conference on Intelligent Robots and Systems in Germany.
"In both cases, the wing is moving back and forth. The only difference is the speed at which the wing flaps."
While it requires 120 flaps per second to remain airborne, the robot only needs to move its wings nine times in water. This is due to the different density of air and water.
"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 Farrel Helbling, the paper's second author.
When it wants to dive, it first positions itself at a certain angle and then stops flapping its wings to crash down and break through the water surface. As the RoboBee is extremely light, it needs to fall down under a certain angle in order to overcome the surface tension of water.
In addition to the different flapping speed, the robot also adjusts the flapping angle once in water.
"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 millimetre-scaled insects to metre-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."
The study was funded by the USA's National Science Foundation and the Wyss Institute for Biologically Inspired Engineering.