A Manta Ray-Inspired Fast-Swimming Soft Electrohydraulic Robotic Fish

Underwater soft robots inspired by marine life have shown great potential in ocean exploration, monitoring, scientific research, etc., due to their excellent safety, compatibility and adaptability when interacting with underwater environments. However, most of their soft actuators suffer performance degradation when operating in water, which leads to the limited cruising speed and maneuverability of underwater soft robots, especially for the electrically actuated ones. Here, we present a manta ray-inspired fast-swimming soft robotic fish based on a new kind of soft electrohydraulic actuator. Two pectoral fin-like actuators are symmetrically arranged to generate flapping motion and propel the robot. An improved electrode encapsulation strategy is proposed for promoting the underwater actuation performance for the actuators, which is also verified by the theoretical analysis, multi-physics simulation and experiments, respectively. The maximum underwater flapping angle can achieve 68 degrees for the encapsulated actuators which is very close to the angle in air. Based on the powerful and noise-free underwater actuation, the soft electrohydraulic robotic fish can swim at an average cruising speed of 111.2 mm/s (2.22 body lengths per second), substantially faster than most of the reported electrically driven soft robotic fish. The robot also has a maximum turning speed of 96°/s with a turning radius of 11.13 cm. This work suggests the high potential of soft electrohydraulic actuators for developing high-performance underwater soft robots, and applicability of our design and waterproof encapsulation strategy for underwater actuation scenarios.