A miniature swimming robot inspired by marine flatworms

Swimming robots play a crucial role in mapping pollution, studying aquatic ecosystems, and monitoring water quality in sensitive areas such as coral reefs or lake shores. However, many devices rely on noisy propellers, which can disturb or harm wildlife. The natural clutter in these environments – including plants, animals, and debris – also poses a challenge to robotic swimmers.

Now, researchers in the Soft Transducers Lab and the Unsteady flow diagnostics laboratory in EPFL’s School of Engineering, and at the Max Planck Institute for Intelligent Systems, have developed a compact and versatile robot that can maneuver through tight spaces and transport payloads much heavier than itself. Smaller than a credit card and weighing 6 grams, the nimble swimming robot is ideal for environments with limited space like rice fields, or for performing inspections in waterborne machines. The research has been published in Science Robotics.

“In 2020, our team demonstrated autonomous insect-scale crawling robots, but making untethered ultra-thin robots for aquatic environments is a whole new challenge,” says EPFL Soft Transducers Lab head Herbert Shea. “We had to start from scratch, developing more powerful soft actuators, new undulating locomotion strategies, and compact high-voltage electronics”.

Miniature electronics for autonomous operation

Unlike traditional propeller-based systems, the EPFL robot uses silently undulating fins –inspired by marine flatworms – for  propulsion. This design, combined with its light weight, allows the robot to float on the water’s surface and blend seamlessly into natural environments.

“Our design doesn’t simply replicate nature; it goes beyond what natural organisms can achieve,” explains former EPFL researcher Florian Hartmann, now a research group leader at the Max Planck Institute for Intelligent Systems in Stuttgart, Germany.

By oscillating its fins up to 10 times faster than marine flatworms, the robot can reach impressive speeds of 12 centimeters (2.6 body-lengths) per second. The robot also achieves unprecedented maneuverability by using four artificial muscles to drive the fins. In addition to forward swimming and turning, it is capable of controlled backward and sideways swimming.

To drive the robot, the researchers developed a compact electronic control system that delivers up to 500 volts to the robot’s actuators at a low power of 500 milliwatts – four times less than that of an electric toothbrush. Despite its use of high voltage, the robot’s low currents and shielded circuitry make it entirely safe for its environment. Light sensors act as simple eyes, allowing the robot to detect and follow light sources autonomously.

The researchers envision the robot contributing to ecological studies, pollution tracking, and precision agriculture, amongst other fields. Next steps involve creating a more robust platform for field tests.

“We aim to extend operating times and enhance autonomy,” says Hartmann. “The fundamental insights gained from this project will not only advance the science of bioinspired robotics but also lay the foundation for practical, lifelike robotic systems that harmonize with nature.”