Molecular robots that build and assemble molecules? Check. Micro-robots that are capable of flying, swimming, diving and breaking out of water? Check. As science and technology continue to delve into the "Nanoland" realm, it stands to reason that the micro-machine tendency will only keep solidifying as more and more scientific researches try to explore the micro-world.
In what appears to be a natural consequence of this trend, a team of scientists from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically-Inspired Engineering at Harvard, managed to create a RoboBee that is capable of flying, swimming, and flying again after diving out of water.

The tiny robot is equipped with floating devices that allow it to stabilize on the water's surface so that an internal combustion system activates to catapult it into the air. Being 1000 times lighter than any previous similar robots, RoboBee opens up a whole new world of possibilities, which range from search-and-rescue operations to environmental monitoring.

Designing such a minute hybrid robot proved to be a strenuous challenge as water is 1000 times denser than air, thus requiring RoboBee to be able to vary its wing speed depending on the environment's nature. Flapping its wings in a low speed would not allow the robot to fly, whereas a rapid flapping frequency in water can cause its them to detach. To meet these requirements, the scientists combined both theoretical and experimental data to create the perfect balance between the wing size and the fluttering rate, enabling the small robot to seamlessly transition from swimming to flying, simply by flapping its wings at nine to 13 hertz in water and 220 to 300 hertz in air. The researchers had also to come up with a solution to tackle the surface tension of water which acts as an obstacle that prevents RoboBee from ascending into the air. To be able to separate itself from water despite its size, RoboBee needs to overcome a surface tension that is measured to be 10 times its weight and three times its maximum lift.

The team solved this problem by providing RoboBee with four buoyant outriggers as well as a central gas collection chamber. During the ascending stage, the chamber acts as a reservoir that collects water from the robot's surroundings and converts it to a combustible gas fuel called oxyhydrogen, using a built-in electrolytic plate. The resulting gas increases the robot's buoyancy, which ultimately causes its wings to break out of water. Then, a small sparker inside the chamber ignites the gas, allowing the robot to propel itself into the air. Finally, a passive stabilization mechanism allows the tiny robot to always land on its feet.

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