Insect-sized robot can go from air to water and back again

Engineers at Harvard University have developed a tiny, insect-like robot — complete with flapping wings — that can fly through the air, land on water and take off again.

At just 175 milligrams, this microrobot inspired by nature weighs one-thousandth as much as previous aerial aquatic robots, and it's the first of its kind to successfully transition from water to air.

The design was reported in the journal Science Robotics Wednesday.

The tiny robot is modelled off species in the animal world that exhibit what is known as "multimodal locomotion," meaning they can manoeuvre — in this case — both in the air and on water.

Lead author Kevin Chen, a postgraduate fellow at Harvard's School of Engineering and Applied Sciences, was studying the physics of small, wing-flapping organisms when he made an observation that would inspire the microrobot's design.

"I realized that flapping in water and flapping in air can be quite similar in the physical sense," said Chen. "What's remarkable is that in water, a species called sea plankton also flap their wings in similar conditions in physics and that really interested me."

Chen said there's growing enthusiasm for developing robots with flapping wings because the propulsion of those wings generates a lot of lift.

The Harvard microrobot — named "Robobee" — can also land on vertical surfaces or perch on overhangs for a unique vantage point

A small-scale robot with the ability to both fly and swim is advantageous for navigating in confined and cluttered environments, such as for search and rescue at the site of a crash landing on water or other disaster, for testing and monitoring water quality of lakes and for tracking insects to learn about them, said Chen.

Design challenges

"Prior to our study, the main challenge is that the robot could not transition from water back into air," he said.

That's because the surface tension of the water is significant relative to a device the size of a common honey bee. In fact, the surface tension effect is 10 times the weight of a microrobot this size.

To overcome this, Chen and his colleagues created a unique onboard power-generating source just to get the Robobee out of the water and back into flight.

The device converts a small amount of surrounding water into hydrogen and oxygen, collects gases in a small air chamber to achieve enough buoyancy to come to the surface, then ignites it for takeoff.

The team is still working on putting a wireless power source on board for the rest of the Robobee's movement.

Behrad Khamesee, a professor of mechanical engineering at the University of Waterloo who has also developed flying microrobots for a number of applications, as well as a small bug-like microrobot for use in surgical procedures, said that's the puzzle facing the field of microrobotics as a whole.

"The biggest challenge is the operating time for this kind of robot at this point," said Khamesee. "Because if they want to be wireless and navigate freely, they should work on an onboard power source. With the tiny batteries on those, the operating time is limited."

Khamesee's own microrobot designs use magnetic energy to generate power on board.

Tiny robots, big advantages

Despite the power source challenge, the scale of microrobots also opens up a world of potential, said Khamasee.

"They consume minimum energy because they're lightweight and they can do many things that a big robot cannot do," he said

"These kind of robots are excellent for inspection, quality control. They can go inside pipes and test for corrosion or cracks, for example."

Because their small scale makes them economical, they can also be used in hazardous environments where they might do an inspection or relay data and then be disposed at minimal cost, he said.

Eric Diller, an assistant professor of mechanical engineering who runs the microrobotics laboratory at the University of Toronto, said medical applications are the other big area of potential for these little robots.

In future "we could actually put small mechanical devices inside the body, maybe with a very small tether or even potentially wirelessly moving inside the body, which would be a revolutionary type of approach to monitoring, taking samples or even doing surgeries inside the body."