Subaquatic robot leverages biomimetics for natural movement

Exploring the underwater world requires robots that can move as naturally as fish and, ideally, blend in as much as possible. That’s exactly what a research group at North Carolina State University has been working on.

A few years ago, the same team designed an aquatic robot inspired by a manta ray. It could swim impressively fast, but it had one major drawback: a lack of three-dimensional maneuverability. Moving forward is one thing, but moving up and down, changing direction, and rotating in place is a whole different challenge. Many underwater robots have that same limitation, so the researchers decided to tackle this problem.

For their latest invention, they took inspiration from the feather star. These marine creatures have multiple flexible, feather-like limbs that help them move in different directions. Watching them, their movements seem almost effortless, but reproducing those maneuvers in robots is very difficult. It would typically require complex control systems and additional actuators – robotic components that produce movement.

But the new robot can maneuver in three dimensions using a few elastic limbs and just two actuators. And that’s exactly what makes it innovative.

“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," explains Jie Yin, corresponding author of a paper on the study. “This is an example of using mechanical intelligence to create a more efficient design.”

So, what exactly does mechanical intelligence imply?

In this case, it refers to designing a robot with more functionality without adding more complexity to it. Rather than assigning a separate motor or control mechanism to every movement, the researchers take advantage of the robot’s physical structure. Its design does some of the work, allowing the robot to move in three different modes.

The first is jellyfish mode.

Jellyfish move through the water by contracting and relaxing their bodies, which makes them rise and descend. The feather star robot uses a similar principle. When both actuators are activated, its feather-like wings snap downward and propel the robot up. Those wings are monostable, meaning they naturally return to their original shape after being bent. As the wings recover, the robot can descend. Repeating this motion faster makes the robot swim through the water, while slowing down allows it to hover in place.

Next is fish mode. Here, only one actuator is activated, creating an asymmetric movement that propels the robot forward or backward. This principle is similar to how a fish uses its fins and tail to swim.

Finally, there’s rotor mode. By alternating the two actuator inputs, the robot can rotate around its own axis, easily changing its orientation.

This is mechanical intelligence in action. Sometimes, building a more capable machine isn’t about adding more electronics – it’s about making the design itself smarter.

The researchers hope that the robot could open up new possibilities for underwater exploration and that it could be used for various applications: from carrying cameras and lifting objects to working alongside other aquatic robots.

Source: North Carolina State University