Imagine an underwater robot that can rise, sink, move forward and backward, rotate in place, and even hover—all without a complicated system of motors and mechanical parts.
Researchers have now developed a soft aquatic robot inspired by feather stars, marine animals known for their graceful and highly flexible movements. Remarkably, the robot can achieve complex three-dimensional movement using just two actuators, the components that generate force or motion.
The new design could provide a simpler and more efficient way to build underwater robots for tasks such as exploring submerged environments, carrying objects, and collecting visual information.
The research, titled “Minimal-Actuation Feather Star–Inspired Soft Swimmers for Multimodal 3D Maneuverability,” was published in Science Advances.
A Robot Designed to Think With Its Structure
One of the most interesting ideas behind the robot is a concept known as mechanical intelligence.
In conventional robots, computers and multiple motors are often responsible for controlling different movements. A robot may need separate actuators to move forward, backward, up, down, rotate, or change direction.
Mechanical intelligence takes a different approach.
Instead of making the control system do all the work, researchers design the robot's physical structure so that it naturally produces useful movements when exposed to simple inputs or environmental forces.
“By taking advantage of intelligent design techniques,” the researchers explain, it is possible to create robotic devices with a surprisingly large range of motion while using very few actuators.
For this feather star-inspired robot, the researchers say a conventional design could require at least six actuators to achieve comparable three-dimensional maneuverability.
Their robot does it with only two.
That reduction could make future aquatic robots simpler, lighter, and potentially easier to control.
Why Feather Stars Were the Inspiration
The robot's unusual design comes from nature.
Feather stars are marine invertebrates with multiple flexible arms or limbs that allow them to interact with water in sophisticated ways. They can move in different directions and can even remain suspended in the water while coordinating their limbs.
Researchers wanted to reproduce some of these capabilities without copying the animal mechanically in every detail.
“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,” said Jie Yin, a professor of mechanical and aerospace engineering at North Carolina State University and the corresponding author of the study.
The result is a soft robot with a relatively simple structure but surprisingly complex movement capabilities.
Four Flexible Wings Do the Work
At the heart of the robot is a central disk containing its two actuators.
Extending from the disk are four flexible wings. These wings are elastic and monostable, meaning they can be bent away from their normal shape but naturally return to that original position when the force causing the deformation is removed.
This simple mechanical behavior is extremely important.
When the two actuators are activated, all four wings snap downward. When the actuators are switched off, the wings return upward.
By controlling how quickly the actuators are switched on and off, researchers can turn the same physical structure into different movement systems.
The robot essentially gets several different swimming behaviors from just two actuators.
Three Modes of Underwater Movement
The researchers demonstrated three major movement modes, each inspired by a different type of swimming behavior.
1. Jellyfish Mode: Moving Up and Down
When both actuators are rapidly activated and deactivated, the four wings repeatedly flap.
This creates forces that push the robot upward through the water.
When the actuators stop, the wings stop flapping and return to their resting position. The robot then descends.
By changing the speed of the flapping, the researchers can also make the robot hover rather than continuously rise or fall.
The researchers refer to this behavior as “jellyfish mode” because it resembles the way jellyfish use rhythmic movements to travel through water.
This ability to control vertical movement is particularly useful for underwater robots, since navigating underwater is not simply about moving across a flat surface. A useful robot must also be able to change depth.
2. Fish Mode: Moving Forward and Backward
The robot can also move horizontally.
Instead of activating both actuators, researchers activate only one.
This causes one of the wings to flutter in a way that resembles the movement of a fish's tail fin.
The resulting force pushes the robot in the opposite direction.
By controlling which actuator is activated, the researchers can make the robot move forward or backward.
This is called “fish mode.”
What makes the approach interesting is that the robot doesn't need a dedicated propeller or separate motor for horizontal movement. The flexible structure itself converts a simple actuator input into useful propulsion.
3. Rotor Mode: Turning in Place
The third movement is rotation.
By rapidly alternating between the two actuators, the researchers create an imbalance in the forces acting on the robot.
This causes the robot to rotate around its own axis.
The researchers call this “rotor mode.”
Combining rotation with forward, backward, upward, and downward movement gives the robot much greater control over its position and orientation.
In other words, it isn't restricted to moving along a single path. It can maneuver through three-dimensional underwater space.
Three Modes Create 3D Maneuverability
The real achievement comes from combining these movements.
Jellyfish mode allows the robot to change its vertical position.
Fish mode provides forward and backward movement.
Rotor mode allows it to rotate and change its orientation.
Together, these three behaviors allow the soft robot to maneuver in three dimensions using only two actuators.
This is especially notable because reducing the number of actuators can also reduce the complexity of the robot's mechanical and control systems.
The researchers previously developed an aquatic robot inspired by a manta ray. That robot was capable of moving quickly through water, but it lacked the ability to maneuver freely in three dimensions.
The feather star-inspired design was created to overcome that limitation without introducing an overly complicated mechanism.
Potential Applications Underwater
The researchers demonstrated several possible applications for the technology.
For example, the robot could carry a camera and move through underwater environments to explore areas that may be difficult for conventional robots to reach.
It could also be used to lift objects underwater.
Multiple robots could potentially work together, allowing them to coordinate their movements and transport objects that are too large for a single small robot.
Because the design is soft and flexible, it could also offer advantages in environments where rigid mechanical systems may have difficulty interacting safely with objects or surroundings.
However, these are still potential applications rather than established commercial uses. More development and testing will be needed before such robots can operate reliably in real-world underwater environments.
The Next Step: Going Wireless
The current system still relies on external components to provide control and power.
One of the researchers' next goals is to develop a fully wireless version.
Removing wires could make the robot much more practical for underwater exploration. A wireless system could allow it to operate more freely without being physically connected to external equipment.
The researchers also hope to collaborate with experts from other fields to explore additional applications.
That could eventually lead to specialized versions designed for underwater inspection, environmental monitoring, scientific research, or other tasks.
A Simple Design With a Big Idea
The feather star-inspired robot demonstrates an important principle in robotics: more motors do not always mean more capability.
By carefully designing the robot's flexible structure, researchers have created a machine capable of several different movements from only two actuators.
The key is mechanical intelligence—the idea that some of a robot's behavior can come from its physical design rather than being controlled entirely by software and electronics.
Nature has spent millions of years developing efficient ways for animals to move through complex environments. By studying those strategies, engineers may discover new ways to build robots that are simpler while still being highly capable.
The feather star robot is a striking example of that approach: four flexible wings, two actuators, and three swimming modes come together to create a machine capable of navigating the underwater world in three dimensions.
The research was published in Science Advances in 2026 by Haitao Qing and colleagues, under the title “Minimal-actuation feather star–inspired soft swimmers for multimodal 3D maneuverability.” DOI: 10.1126/sciadv.aeg9211.
Reference: Haitao Qing et al, Minimal-actuation feather star–inspired soft swimmers for multimodal 3D maneuverability, Science Advances (2026). DOI: 10.1126/sciadv.aeg9211. www.science.org/doi/10.1126/sciadv.aeg9211
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