An eel-like robot based on a dielectric elastomer

Potential applications include underwater exploration, environmental monitoring, and operations where maneuverability and low environmental impact are required.

The design was inspired by the long-distance migration and high-endurance cruising behavior of real eels, which led to research into robots that mimic their high efficiency, strong maneuverability, and high stability.

Dielectric elastomers (DEs), which are smart, soft materials that deform significantly under an electric field, are used as the primary actuator.

DEs have large strain, fast response, light mass, and can be easily integrated into soft actuators suitable for underwater robots, providing unique advantages like flexibility and high energy efficiency.

The robot can realize an S-type angle swinging motion similar to a real eel, though there are differences in amplitude distribution along the body, specifically with a larger head amplitude in the robot.

The main components are five connected driving modules, a head part, a tail part, and a tail fin.

Actuation is achieved with tubular dielectric elastomer actuators mounted on circular frames, forming series-connected drive modules.

The maximum propulsion speed recorded was 43.7 mm/s at a frequency of 1.5 Hz.

The designed robot’s maximum speed (43.7 mm/s) exceeds that of Shintake's bionic robot (37.2 mm/s) by a factor of 1.18.

The swim number is the ratio of the advancing body length to the distance pushed by the tail fin, representing propulsion efficiency. The robot’s highest swim number was 0.15, much lower than the typical fish value around 0.6, indicating lower efficiency.

The robot’s head amplitude was larger than the tail, opposite to real fish, and there was more energy wasted in lateral motion, reducing swimming efficiency.

At higher frequencies, propulsion speed decreased, likely due to the intrusion of insulating fluid increasing the robot’s weight and possibly the robot’s responsiveness limitations.

Future improvements could involve designing a sealed, closed structure to prevent fluid from entering and increasing the robot’s mass and drag.

Soft and compliant drives reduce the risk of damaging the environment or wildlife, enhance maneuverability in confined spaces, and can safely interact with delicate structures.

Suggestions include optimizing the drive frequency response, improving fluid sealing, and adjusting mass and rigidity to better match natural eel swimming and improve efficiency.

A traveling wave (gait) equation is used, where each joint’s angle is governed by a sinusoidal function with amplitude, frequency, phase shift, and offset terms.

A camera recorded the robot as it was actuated by a high-voltage, variable-frequency power supply in a bath of insulating liquid, and X-coordinate positions were analyzed to calculate speed.

Fluorinert is an electrically insulating, transparent, thermally stable liquid that prevents electric short circuits during high-voltage actuation in the tests.

With constant body swing and wavelength, increasing frequency raises propulsive force and input power but reduces efficiency; with constant frequency and wavelength, increasing swing raises all four measures.

A detachable male and female connection mechanism was used, allowing individual drive modules to be easily replaced if damaged.

The modular design makes maintenance easier and increases adaptability, while flexibility enables operation in narrow or complex spaces.

Potential applications include underwater exploration, environmental monitoring, and operations where maneuverability and low environmental impact are required.

The design was inspired by the long-distance migration and high-endurance cruising behavior of real eels, which led to research into robots that mimic their high efficiency, strong maneuverability, and high stability.