Batoid‑inspired robots also use various electrically driven actuators composed of two electrodes that sandwich another material. Credit: npj Robotics (2026). DOI: 10.1038/s44182-025-00064‑x

Underwater robots face many challenges before they can truly master the deep, such as stability in choppy currents. A new paper published in the journal npj Robotics provides a comprehensive update of where the technology stands today, including significant progress inspired by the movement of rays.

Underwater robots are not a gimmick. We need them to help us explore the roughly 74 % of the ocean floor that still remains a mystery. While satellites, buoys and imaging technology can map the surface and the upper reaches of the ocean, we need underwater drones to explore and gather data from the hidden depths.

Ray‑inspired robots

The solution, as with many engineering challenges, comes from nature. To overcome the limitations of traditional propellers and improve maneuverability, researchers have developed ray‑inspired robots. These machines mimic the flat, efficient shape of the ray’s body, which allows them to glide through the water and stay steady even when currents are strong.

“Ray‑inspired robots have generally followed the pectoral fin aspect ratio and locomotion style trends seen in natural rays: higher width‑to‑length aspect ratios are mainly seen in oscillatory rays, whereas lower aspect ratios are seen in undulatory rays,” commented the researchers in their paper.

In the review, the team looked at 47 ray‑inspired robots, comparing how they move and navigate. They found several kinds of actuators that move the wings. The most common were standard electric motors (servos) that work well for larger robots but can be too heavy or rigid for smaller designs.

Other ray‑fin robots use soft‑balloon‑like pads that inflate with air or water to bend the wings, and some use smart materials that change shape when triggered by an electric signal. There are even microscopic robots powered by living heart cells that contract to create a flapping motion.

Size matters

One of the most significant findings was that when it comes to performance, size matters. Tiny robots roughly the size of a coin work well with flexible materials that bend when hit by a pulse of electricity. Similarly, large robots the size of dinner plates work well with traditional motors.

The problem is the middle‑sized range robots. At this scale, electric‑pulse materials aren’t powerful enough to push them through water, and traditional motors are often too heavy. The search for a solution continues.

While the review authors state that great strides have been made in movement, the next big challenge is equipping robots with the ability to sense water and artificial intelligence to navigate.

More information:

Luke Freyhof et al., “Ray‑inspired robots: recent advances in actuation and control,” npj Robotics (2026). DOI: 10.1038/s44182-025-00064‑x.