She quickly changes the medium and can hitchhike: Researchers have developed a drone that can move both in water and in the air and is equipped with a sophisticated “sticking organ”. Tests show that its suction disc, inspired by the remora fish, allows it to stably attach itself to surfaces in the water and on land. For example, the drone could also save energy when traveling on ship hulls or whale bellies. This makes the concept particularly suitable for the biological and ecological monitoring of marine ecosystems, say the scientists.
They whiz through the air in ever more sophisticated versions, and scientists have already developed many autonomous robotic systems for use in water. However, the goal of a team of scientists from China, Great Britain and Switzerland is now to produce powerful combinations of these concepts. Because the possibility of a flexible change between the media air and water could open up some interesting application potentials, especially in the exploration of the environment.
In addition to optimizing the drive system, an important aspect in the development of the team’s current model was extending the range without having to rely on battery systems. Giving drones more freedom from base stations could improve their potential for research missions in vast or remote areas. The scientists are now presenting the prototype of a hybrid drone that is suitable for operations both in the air and in the water and that can reduce its energy requirements by “hitchhiking”.
Refined propellers and biomimetic adhesive power
The basic concept is based on the construction of conventional quadrocopter drones with four drive units. The special adjustment for the change between water and air is the clever design of the rotors: When propelled in the liquid medium, the blades of these units adopt an angled position via a flexible joint to form more the shape of a ship’s propeller. As soon as they reach the surface, however, they stretch out due to the increased speed and the associated centrifugal forces and thus form a propeller shape. This passive ability to transform drives the drone optimally in both media and the change can take place surprisingly quickly: the researchers report that the morphing propeller crosses the air-water barrier in 0.35 seconds.
For the design of the hybrid drone’s adhesive element, the scientists took their inspiration from nature. They studied in detail the organ through which the remora fish (Echeneis naucrates) attaches itself to marine animals in order to be taken away by them. It is a disk made up of different chambers. They form a set of suction cups that use negative pressure to provide adjustable adhesion. The compartments ensure that the connection can also hold on surfaces with complex structures. The remora fish even sticks to the skin without any problems when dolphins and co. jump out of the water.
Hitchhiking on the way
The new adhesive element that the researchers have developed is now based on the same basic concept as the fishy role model. An elastic polymer material forms compartments that provide negative pressure as soon as the element comes into contact with surfaces due to changes in shape generated by hydraulic systems. This enables strong adhesion that can be easily released again if necessary via the device control. The developers’ prototype has one such attachment member at the top and one at the bottom of its central unit. Tests of the concept confirmed that the adhesive disk can securely attach the robot not only to wet, but also to dry surfaces of different textures.
The practical potential of the concept was also confirmed in application-related tests: the scientists had the hybrid drone docked to the hull of a watercraft so that it could be taken along. This resulted in video recordings of the seabed, such as hermit crabs, scallops and seaweed. The hitchhiking robot itself hardly used any energy. During the tests, the team was also able to document that the robot can perform various tasks in both fresh and salt water.
“We have successfully implemented the adhesion mechanism of the remora fish and combined it with robot systems to achieve novel mobility methods for robotics,” says co-author Mirko Kovac from the Swiss Federal Laboratories for Materials Science and Technology in Dübendorf, summing up the result of the work. In conclusion, the scientists write: “We believe that our results now pave the way for the development of autonomous robots with different functions in a variety of air and water environments.”
Source: Federal Materials Testing and Research Institute, specialist article: Science Robotics, doi:10.1126/scirobotics.abm6695
Video © Empa (Source: Beihang University / Science Robotics)