Feather Star-inspired Underwater Robot Gets 3D Maneuverability From Only Two Actuators
For Immediate Release
Researchers have created an aquatic soft robot inspired by marine invertebrates called feather stars. The feather star robot is able to move through the water in all three dimensions, powered by only two actuators.
“One exciting aspect of this work is that it demonstrates how we can create robotic devices with an incredible range of motion using a minimum number of actuators, by taking advantage of intelligent design techniques,” says Jie Yin, corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at North Carolina State University. Actuators are the parts of a machine that provide force or torque.
The feather star robot’s design draws on a concept called mechanical intelligence. This refers to dynamic objects – like robots – whose behavior is governed largely by their structure and how they interact with their environment, reducing the amount of input necessary from computers or human users.
“In this case, we created an aquatic soft robot that can move in three dimensions – up and down, forward and backward, and rotating on its axis,” Yin says. “Normally, you would need at least six actuators to accomplish this. But due to its structural design, we accomplish this range of motion with only two actuators in the feather star robot. This is an example of using mechanical intelligence to create a more efficient design.” Video of the feather star robot can be seen here: https://youtu.be/UHdcii-Icjs.
“We had previously created an aquatic robot inspired by a manta ray, and that design was capable of moving quickly through the water – but it did not have three-dimensional maneuverability,” says Haitao Qing, first author of the paper and a postdoctoral researcher at UC Berkeley who began work on this project while a Ph.D. student at NC State. “Our goal with this work was to design a robot that had greater maneuverability without relying on unduly complicated mechanisms.”
“We were inspired by feather stars because they are able to move in any direction or hover in place by coordinating the movement of their limbs,” says Yin.
The feather star robot has four “wings” protruding from a central disk that contains two actuators. The wings are elastic and monostable, meaning the wings can be bent but will snap back to their original position. When both actuators are activated, all four wings snap down – and when the actuator is turned off, the wings snap back up. By rapidly activating and deactivating both actuators, the robot flaps its wings quickly and rises in the water column. When the actuators are turned off, the wings stop flapping and the robot descends in the water column. And by flapping its wings slowly, the robot is able to hover in place. The researchers call this “jellyfish mode.”
To move forward or backward, the researchers only activate one actuator. This makes one wing flutter, like a tailfin, pushing the robot in the opposite direction. The researchers call this “fish mode.”
And by alternating rapidly between the two actuators, the researchers can make the robot rotate on its axis, allowing them to steer the robot in any direction. The researchers call this “rotor mode.”
“By combining these three modes, we can maneuver the robot in all three dimensions,” says Yin.
The researchers demonstrated the potential utility of the robots by showing how they can be used to explore underwater spaces with a camera, or can lift objects underwater either alone or by working in concert with other robots.
“This design offers a versatile platform for integrating with other technologies for use in various underwater applications,” says Qing. “Future directions for this work include developing a fully wireless version. Also, we are mechanical engineers, and we’ve created a novel design for aquatic robotics. We would welcome collaborating with experts in other fields to explore potential applications for this design.”
The paper, “Minimal-Actuation Feather Star–Inspired Soft Swimmers for Multimodal 3D Maneuverability,” is published in the open access journal Science Advances. The paper was co-authored by Caizhi Zhou and Haoze Sun, both Ph.D. students at NC State; Yuanhang Zhu of the University of Virginia and University of California, Riverside; and Jiacheng Guo, Haibo Dong and Daniel Quinn of the University of Virginia.
This work was done with support from the National Science Foundation under grants 2126072 and 2329674; and the Office of Naval Research, under MURI grant N00014-22-1-2616. Qing and Yin are coinventors on a pending patent invention disclosure filed by North Carolina State University that is related to this work.
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Note to Editors: The study abstract follows.
“Minimal-Actuation Feather Star–Inspired Soft Swimmers for Multimodal 3D Maneuverability”
Authors: Haitao Qing, Caizhi Zhou, Haoze Sun and Jie Yin, North Carolina State University; Yuanhang Zhu, University of Virginia and University of California, Riverside; Jiacheng Guo, Haibo Dong and Daniel Quinn, University of Virginia
Published: Oct. 7, Science Advances
DOI: 10.1126/sciadv.aeg9211
Abstract: Complex, three-dimensional (3D) motions typically require actuator arrays and complex control architectures. Here, we present a feather star–inspired soft robotic swimmer that uses only two pneumatic inputs to produce three distinct and switchable swimming modes: jellyfish-like pulsation, fishlike propulsion, and rotor-like reorientation. The robot owes this ability to mechanical intelligence: It leverages a monostable instability in its flexible arms to convert two control actuation inputs into 3D swimming modes, including ascension and descension, forward and backward swimming, hovering, and rotation. The robot achieves a maximum swimming speed of 1.64 body lengths per second, minimum cost of transport of 17.6, and peak rotation speed of 90° per second. Particle image velocimetry analyses and computational fluid dynamics simulations reveal distinct vortex structures governing thrust generation and/or rotational torque in each swimming mode. The robot’s minimal input yet multimodal output demonstrates how mechanical intelligence can enable adaptive and multifunctional, yet simple and energy-efficient, robotic and biological swimming mechanisms.
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