[Image] A vehicle that moves in both air and water presents fundamental physical challenges, particularly during the transition from water to air. But nature could hold the key to developing a robot capable of a smooth water/air transition. Credit: Imperial College London, YouTube
Designing a vehicle that both flies and drives on the ground presents sometimes conflicting design requirements, as the Goodyear tire design debuted in March illustrates. Similarly, a vehicle that moves in both air and water presents fundamental physical challenges as well—particularly during the transition from water to air.
“One of the most power-intensive processes is the transition from water to flight, which requires rapid acceleration to the speed required for flight, due to the presence of additional drag and added water mass,” researchers write in a recent paper.
The researchers—from Imperial College London in the U.K.—explain several recently-developed systems feature aerial-aquatic locomotion capabilities, but these systems do not demonstrate both consecutive and complete transitions to flight from water. Additionally, some electric brushless rotor vehicles operate in both media, but the transition to flight “is typically constrained to very calm sea conditions because they risk being partially or fully submerged by waves that are larger.”
In their study, the researchers looked to create a vehicle capable of a smooth and complete water/air transition by developing a method that produces a high amount of power for a short time period that is insensitive to water immersion.
To develop such a method, the researchers looked to nature for inspiration.
Several animals perform water-to-flight transitions, but it wasn’t a fish or bird that inspired the researchers. Instead, that honor goes to a group of less well-known animals—flying squid.
The term “flying squid” applies to several species of squid that launch themselves into the air by filling their mantle with water and then forcefully expelling the water through a siphon (flexible tube) below their head. Whether this propulsion should count as “flying” or “gliding,” marine biologist Silvia Maciá, who coauthored a 2004 report on flying squids, argues for the former.
“From our observations it seemed like squid engage in behaviors to prolong their flight,” Maciá says in a Scientific American article. “One of our co-authors saw them actually flapping their fins. Some people have seen them jetting water while in flight. We felt that ‘flight’ is more appropriate because it implies something active.”
Regardless of the term used, the Imperial researchers aimed to mimic this jetting technique in their robot.
“We have used water-reactive chemicals [calcium carbide powder] to reduce the materials that the robot needs to carry,” Mirko Kovac, lead researcher and director of the Aerial Robotics Laboratory at Imperial, explains in the press release. “Since the chamber fills passively and the environmental water acts as a piston, we can create a full combustion cycle with only one moving part, which is the pump that mixes the water with the fuel.”
The robot, which weighs only 160 grams, generates a force 25 times its weight, giving it a greater chance of overcoming waves compared to other aerial-aquatic systems. The team tested the robot in a lab, lake, and wave tank and showed it can escape from the water’s surface even under relatively rough conditions—traveling up to 26 meters (85 feet) through the air after take-off!
In the press release, first author and Ph.D. candidate Raphael Zufferey says low-power, tether-free robots like theirs “could be really useful in environments that are normally time- and resource-intensive to monitor, including after disasters such as floods or nuclear accidents.”
The researchers are now working with partners in Switzerland to build new vehicles and to conduct field trials of the robot in a range of environments, including monitoring the oceans around coral reefs and offshore energy platforms.
See the robot in action in today’s video below!
The paper, published in Science Robotics, is “Consecutive aquatic jump-gliding with water-reactive fuel” (DOI: 10.1126/scirobotics.aax7330).
Credit: Imperial College London, YouTube