Modular Platform for the Exploration of Form-Function Relationships in Soft Swimming Robots

Abstract

Biological fish differ widely in anatomical structure (body stiffness, fin, body length, etc.) and swimming gait, and it is known that their physical characteristics have a close correlation to their locomotion capabilities. By systematically studying these correlations between the soft body structures of a fish-vertebrate-mimicking swimming robot and its swimming efficiency, we can elucidate the relationships between form and function and provide guidance on the design of novel nonbiomorphic swimming robots capable of performing complex underwater maneuvers.In this work, we design a soft modular swimming robot platform to systematically explore the relationship between body structure, swimming gaits, and locomotion performance. The proposed one degree of freedom (DOF) swimming robot platform includes an underactuated, cable-driven design that mimics the cascaded skeletal structure of soft spine tissue and hard spine bone seen in many fish species. The cable-driven actuation mechanism is oriented laterally for forward or backward motion and steering in a 2D plane. The modular platform design allows for easy modification of morphological parameters such as fin configuration, soft joint stiffness distribution, and body length, to vary the robot’s swimming mode.During experiments, we varied the swimming robot design and actuation parameters over multiple trials and observed the emergent locomotion behaviors in a controlled, underwater testbed. Results showed that the swimming robot is able to achieve biomorphic swimming modes which change from oscillatory (2.3 cm/s) to undulatory (11.0 cm/s) by simply tuning motor oscillation frequency. In addition, unnatural, nonbiomorphic swimming behaviors, such as the ability to change the swimming direction from forward to backward at different actuation frequencies, were also observed for certain joint stiffness and fin configurations.