Recipes for Emulating Nonlinear Active Materials with Robotics*

Within the area of wave propagation through nonlinear phononic media, there are still many practical challenges that remained to be solved, such as the physical realization of specific nonlinear and non-conservative multibody interactions. In this work, we demonstrate that programmable interactions between undulatory robots can be a versatile tool for studying nonlinear wave propagation that relaxes the limits necessitated by constituent materials and geometry. We perform simulations and experiments of simple virtually-coupled undulatory robots with one rotational degree of freedom that actively interact via torque control based on instantaneous position measurement. There is no need to integrate feedback signals and no central control of the system, except for local interactions. The theory and experiments in this study show how programmed robotic interactions can not only emulate the behaviors of nonlinear active materials with potential applications across multiple disciplines of physics and engineering, but also serve as a foundamental step in design and development of new robotic and mechanical metamaterials.