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A High-Flying Aquatic Robot

Zufferey, A. Ortega Ancel, A. Farinha, R. Siddall, S. F. Armanini, M. Nasr, R. V. Brahmal, G. Kennedy and M. Kovac. Consecutive aquatic jump-gliding with water-reactive fuel. Science Robotics, 2019. DOI: 10.1126/scirobotics.aax7330

A newly-developed robot capable of swimming and flying, using water-reactive fuel to launch itself from water. Source: Zuffery et al. 2019

From self-driving cars, to delivery drones, to the Roomba whizzing around your home, robots are fast becoming a part of our daily lives.  Now, researchers at Imperial College London have invented a robot that can swim and fly – and even launch itself from water like a rocket jet.


Mission: Impossible

Working in aquatic areas – lakes, water reservoirs, the vast ocean – is extremely costly in terms of time and resources.  Some environments, such as Arctic regions or those affected by manmade or natural disasters, are too remote or dangerous for humans to access.  How can we minimize the manpower and risk to humans associated with environmental monitoring, reservoir management, and disaster response?

One solution is to use robots to carry out these tasks for us.  While robots that can operate either in air or in water do exist, few systems are capable of both swimming and flying and transitioning seamlessly between the two worlds.   These so-called “aerial-aquatic” robots would have myriad uses in aquatic missions.  They could efficiently map oil spills and toxic wastes.  They could assist search and rescue operations during floods, hurricanes, and nuclear accidents.  And they could monitor coral reefs both underwater and from a birds-eye view.


Float Like a Butterfly, Jump Like a Squid

A flying squid in action. Source: Oceanwide Expeditions

Designing a small robot that can efficiently move through air and water is no easy feat.  As you can probably attest if you’ve ever felt like a beached whale heaving yourself out of the swimming pool, launching from water requires a lot of power.  The robot needs to be powerful enough to complete the water-to-air transition, but light enough for flight.  Scientists have previously developed robots which can complete this transition, but they can typically only operate under very calm sea conditions, limiting their effectiveness.

To tackle this challenge, the authors of this study looked to Mother Nature for inspiration.  One of the biggest evolutionary pressures animals face is to be able to hunt, forage, and migrate – which requires moving through varied terrain – at minimal energetic cost.  Here, the scientists modelled the design of their robot after the flying squid, which can jump from water by releasing a pressurized water jet before gliding back into the sea.


3, 2, 1… Blast Off!

In order to create a jet powerful enough for their robot, the scientists designed a novel water thruster, which essentially acts like a rocket jet.  Instead of storing fuel onboard, which would add to the complexity and weight of the robot, the thruster produces gas on the fly by reacting two separate stable components, much like your car air bags.  Here, water taken from the surrounding environment reacts with a thimbleful of calcium carbide powder to produce combustible gas.  When it’s time, the gas is ignited – and the robot blasts off.


Squid Rocket Science

To optimize the performance of their robot before constructing a prototype, the team developed an analytic physics model.  Their main goal was to maximize the distance travelled per jetting cycle; the farther the robot can fly, the more useful it is in potential missions.  Using the results from the model, the scientists determined the best value for different parameters, such as the engine nozzle size and launch angle.

The resulting robot weighed in at 160 grams (about the same as a hockey puck).  It generates a force 25 times its weight, allowing it to take off even under wavy conditions.  And, rather than depending on electricity, it can jump again and again by simply refilling its tank with water.

Overview of the aerial-aquatic robot design. Source: Zuffery et al. 2019


(Water) Gives You Wings

The team first tested their robot under controlled conditions in a water tank, before graduating to a pond in the great outdoors.  In total, the robot successfully completed 22 flights, even under windy conditions.  It was able to accelerate to 10 m/s (3.3 ft/s) in 25 milliseconds, soaring distances up to 26 meters (85 feet) before gracefully gliding back to the water surface.

This is a promising start, but there is still more to do. One limitation of the current robot prototype is that it takes 20 minutes for its tank to refill with water.  Ideally, filling times would be shorter so that it could complete consecutive jumps faster.  In terms of mileage, including a low-power propeller would allow the robot to fly across larger swaths of water.  Lastly, by making the robot autonomous, it could cruise around without direct human supervision.

Flight test of the robot in a pond. From left to right: floating, takeoff, jetting, and gliding. Source: Zuffery et al. 2019

The team is already working to build next-generation versions of the robot.  Planned field trials will take place in variety of environments, such as in the ocean to monitor coral reefs and offshore energy platforms.  All in all, the aerial-aquatic robot promises to usher in a new era of improved water quality monitoring, search and rescue operations, and underwater exploration.  ■


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