A University of Southampton-led research team has revealed an adaptive robotic wing equipped with tiny sensors that detect and react to changes in water, offering a previously unattainable level of stability and energy efficiency in swimming robots.
Inspired by the movements of birds and fish that can sense small disturbances in the currents and adapt on-the-fly by changing the shape of their wings and fins, the Southampton team’s adaptive robotic wing could help engineers close the maneuverability and efficiency gaps between flying and swimming robots and actual birds.
Robotic Wing Inspired by Birds and Fish
Most human-made aircraft that employ wings are rigidly designed to resist buffeting from changing wind conditions. Still, the ability to power through shifting currents comes at a cost to maneuverability and efficiency. Aquatic platforms, including submersibles, semisubmersibles, and autonomous robotic vehicles, face similar challenges, often necessitating trade-offs between efficiency and maneuverability.
According to the research team behind the adaptive robotic wing, which includes scientists from Edinburgh and Delft in the Netherlands, although engineers are still searching for improvements, nature has solved many of these problems using proprioception. Described as the body’s internal sense of position, movement, and force, proprioception allows birds to sense changes in air flow with their feathers and adapt accordingly. Fish use the same ability thanks to a sensitive lateral line system that detects changes in water currents.
Curious whether they could imbue robots with an artificial version of proprioception, the research team developed an ‘e-skin’ that can be applied to the surface of a robotic platform. According to a statement detailing the adaptive robotic wing, the e-skin consists of flexible, liquid-metal wires encased in silicone that “act like nerves,” sensing when the wing bends.
In the team’s prototype version, the signal from the e-skin’s artificial nerves indicating a current sends the signal to the wing body containing two hydraulically pressurized tubes. After receiving the detected current, the hydraulic tubes can instantly and automatically respond by changing the wing’s stiffness and camber.
According to Leo Micklem, lead author of the study detailing the wing’s development, their design took the opposite approach to rigid robotic wings that resist the current with rigidity and power, copying nature’s more efficient, more maneuverable approach.
“Instead of building ‘tougher’ robots designed to fight the ocean’s power, we are moving toward smarter, softer machines that work in synergy with the environment,” explained Micklem, who designed and tested the robotic wing at the University of Southampton and is currently at Portland State University.
E-Skin Equipped Robot Outperforms Gliding Barn Owl
After completing their e-skin-equipped robotic wing, the research team performed several tests designed to evaluate its ability to adapt to currents. According to the team’s statement, after subjecting the wing to disturbances of “different shapes and magnitudes,” they compared the results to existing standard wing designs. This included rigid wings and basic soft wings without proprioceptive abilities.
The team said the results of the comparison were “staggering.” The adaptive robotic wing not only outperformed the other human-made options, but its ability to stabilize itself was roughly double that of a typical barn owl when gliding.
Although the research team warned that “direct comparisons should be interpreted with caution,” they also noted that the wing’s unprecedented adaptive capabilities made it highly energy-efficient. Instead of resisting the current like stale wing craft, the e-skin-equipped wing sensed its surroundings and seamlessly adapted to them, resulting in tremendous energy savings.
Emerging Materials and Scaling Challenges
When discussing the potential benefits of their adaptive robotic wing, Southampton professor and study co-author Blair Thornton said its energy savings and increased maneuverability could pave the way for more agile, safer robots that use much less energy to maintain stability in windy or turbulent conditions. This includes robots that operate in ocean environments that are “dynamic and unpredictable,” necessitating the ability to rapidly sense changes and react by altering the wing’s shape and position.
“Emerging approaches have demonstrated efficient propulsion using soft materials, but integrating these materials for sensing and control brings soft robots closer to the adaptive systems needed to operate reliably in natural underwater settings,” Professor Thornton explained.
Although the current version of the adaptive robotic wing has only been tested in a lab setting, the research team is already outlining the challenges they will need to overcome to reach a commercially viable system. Among the most pressing concerns raised by Micklem and colleagues were scaling up the technology, integrating it with the rigid components of existing Autonomous Aerial Vehicle (AUV) platforms, and improving its robustness in real-world situations. They are also exploring whether more powerful actuators could further enhance the adaptive robotic wing’s stability.
The study “Harnessing proprioception in aquatic soft wings enables hybrid passive-active disturbance rejection” was published in npj Robotics.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.