Sliding-Layer Laminates: A Robotic Material Enabling Robust and Adaptable Undulatory Locomotion

Abstract

Continuum robots that move through undulatory actuation must be composed of body materials that can enable flexible movement yet also provide resistive forces to the surrounding fluid, granular, or solid environments. This need for “f1exible-yet-stiff” materials is notably important in robot designs that use passive propulsive elements such as tails and wings. Here we explore a laminate design paradigm for “f1exible-yet-stiff” robotic materials through sliding layer laminates (SLLs). We present design principles motivated by theory and experiment and illustrate a taxonomy of SLL enabled morphable materials capable of up to 7 fold change in stiffness. Lastly, we demonstrate the applicability of SLLs to undulatory continuum robots: a swimming robot with a passive tail. We target two desired robot locomotor behaviors: fast open water swimming, and steady swimming through narrow channels emulating underwater caverns and pipes. We demonstrate how tuning the stiffness of the robot tail maximizes thrust generation in these two locomotion modes. Soft tails are optimal in confined swimming because they generate short amplitude high wavenumber oscillations, while stiff tails in confined environments either collide with the walls or do not generate sufficient thrust. However, stiff tails are far better in unconfined environments which enable large stroke amplitudes requiring high stiffness. Through this demonstration we show that stiff or soft tail designs alone are incapable of effective locomotion in complex underwater environments challenge.