# Hybrid-Actuated Multimodal Cephalopod-Inspired Underwater Robot

## TL;DR

A new robot inspired by cephalopods uses a hybrid actuation system to improve underwater maneuverability and adaptability in shallow environments.

## Contribution

The robot introduces a hybrid drive system combining undulating fins, water-flapping tentacles, and a CoG adjustment module for enhanced underwater control.

## Key findings

- Undulating fin thrust scales quadratically with oscillation frequency, matching hydrodynamic theory.
- The robot achieved a turning radius of approximately 15 cm through differential fin control.
- Field trials confirmed robust performance in shallow, confined underwater environments.

## Abstract

To overcome the limitations in maneuverability and adaptability of traditional underwater vehicles, a novel hybrid-actuated, multimodal cephalopod-inspired robot is proposed. This robot innovatively integrates a hybrid drive system wherein sinusoidal undulating fins provide primary propulsion and steering, water-flapping tentacles offer auxiliary burst propulsion, and a gear-and-rack center-of-gravity (CoG) adjustment module modulates the pitch angle to enable depth control through hydrodynamic lift during forward motion. The effectiveness of the design was validated through a series of experiments. Thrust tests demonstrated that the undulating fin thrust scales quadratically with oscillation frequency, aligning with hydrodynamic theory. Mobility experiments confirmed the multi-degree-of-freedom control of the robot, demonstrating effective diving and surfacing via the CoG module and high maneuverability, achieving a turning radius of approximately 15 cm through differential fin control. Furthermore, field trials in an outdoor artificial lake with a depth of less than 1 m validated its environmental robustness. These results confirm the versatile maneuvering capabilities of the robot and its robust adaptability to confined and shallow-water environments, presenting a novel platform for complex underwater observation tasks.