Design of an Untethered Multi-Mode Swimming Robot Driven by Electromagnetic Actuators

Abstract

Underwater robots have significant potential for a wide range of applications, including deep-sea exploration, hydrocarbon extraction, marine biodiversity observation, and waste retrieval. A hybrid actuation system that combines electromagnets and permanent magnets preserves the main benefits of magnetic-driven robots, addressing the issues of bulky coil systems and limited mobility. However, most electromagnetically actuated underwater robots are limited to a fixed swimming mode due to their relatively simple designs, which restrict their adaptability to unpredictable and unstructured aquatic environments. In this work, we present an untethered multi-mode swimming robot driven by four 2-degreesof-freedom (DoF) electromagnetic actuators, each with a rigid shell interconnected by flexible connectors and covered with silicone membranes. Initially, we conducted tests to determine the optimal hardness of the flexible connector by validating the module’s range of motion across different activation times. Next, we demonstrated that the robot can swim forward and backward in a water tank, exhibiting snake-inspired motion, front- and rear-undulation, and wave-shaped motion, and reaching a maximum speed of 87.8 mm/s. Finally, we showed the lateral translation and steering motions achieved with different control signals, resulting in an average turning speed of 3◦/s. This approach enables a novel robot design strategy based on compact multi-DoF electromagnetic modules, facilitating potential applications in search-and-rescue missions and environmental inspections.