Bioinspired Shape-Changing Soft Robots for Underwater Locomotion: Actuation and Optimization for Crawling and Swimming

Many existing rigid underwater robots use propellers to create thrust. These traditional robots are widely used because they are capable of moving large payloads at high speeds through open water. However, the movement patterns exhibited by soft underwater organisms suggest that there are alternative locomotion methods that robots can use to be more efficient, less disruptive to the environment, and to navigate confined spaces more easily than current rigid robots. Biological strategies that have survived through the evolutionary process can be used as inspiration to create robust locomotion of robots using soft materials. This chapter reviews how soft, underwater organisms change their shapes to enhance motion, catalogues how researchers have used soft active materials to mimic these abilities, and discusses how recent work uses optimization to produce more effective underwater robotic locomotion. We categorize underwater locomotion into crawling and swimming, where crawling uses contact with a solid substrate for moving through the fluid, and swimming relies purely on hydrodynamic forces for propulsion. We summarize the main categories of actuators for soft robotics with a focus on how these actuators can be used to create shape-changing mechanisms. By further categorizing the state-of-the-art in bioinspired robotic locomotion for different types of crawling and swimming motions, we identify future avenues for research. We also detail how optimization can be used to design robot components and behaviors, and to explore how active online optimization of design parameters can improve robot performance. The biological inspirations and engineering applications described in this chapter form the basis for the design of soft underwater robots that locomote effectively by creating favorable interactions with fluid environments.