A Novel Omnidirectional Swimming Robot with Articulated-Compliant Legs

Stability, adaptability, and maneuverability are crit- ical performance indexes for underwater biomimetic robots, espe- cially in narrow spaces. However, these aspects can sometimes be contradictory. This paper presents an omnidirectional swimming robot inspired by the whirligig beetle and designed to achieve good performance in stability, adaptability, and maneuverability. Its design features four novel articulated-compliant robotic legs, and its hydrodynamic model is formulated using Kirchhoff’s equation and the Lagrangian method. The hydrodynamic forces are calculated using the quasi-steady flow model, and extensive experiments are carried out to examine thrust generation and speed. It is found that this omnidirectional robot has significant improvements compared to a conventional robot with a single passive joint in its leg. Specifically, its swimming speed is as fast as 0.34 m/s with a frequency of 1.4 Hz, which is a 30.8% increase. Moreover, the robot’s multimodal swimming capabilities is demonstrated, such as swimming forward, retreating, lateral swimming to the left or right, zero-radius turning, and no zero- radius turning, by configuring different locomotive patterns of the articulated-compliant legs. The passing and collision experi- ments demonstrate the robot’s potential applications in narrow spaces. Overall, this omnidirectional swimming robot strikes a great balance among stability, adaptability, and maneuverability, providing a promising solution for high-performance underwater vehicles.