Agile robotic fish based on direct drive of continuum body

Fish-like agile movements, such as fast forward swimming and rapid turning, are essential for robots to perform a wide variety of tasks in aquatic environments. However, achieving these locomotion capabilities simultaneously in existing biomimetic underwater robots has proven challenging. Here, we present a self-contained robotic fish capable of swimming at a speed of 6.3 body length per second and pivot turning at an angular speed of 1450° per second. These fast motions, which compare well with those of real fish, are realized by directly oscillating a flexible body using an electromagnetic motor. This direct-drive (DD) method eliminates the need for transmission parts, simplifies the robotic structure, improves mechanical robustness, and enables the use of a flexible continuum body that passively interacts with water, generating fish-like body deformations and subsequent rapid swimming. This also allows the robot to have the Strouhal and swimming numbers that match the typical values observed in nature. Moreover, the observed frequency peaks in swimming are similar to computed values using a model, which guides the design of the robot. These results illustrate the DD method as a promising framework for the creation of highly versatile biomimetic underwater robots.