Optimization of Soft Robot Swimmer Using Lighthill's Large-amplitude Elongated-body Theory

Long slender organisms demonstrate remarkable proficiency in varied terrain and especially water. The success of these organisms inspires novel designs in various fields especially robotics. Recent advances in robotic fabrication techniques have led to a new class of "soft robots". Soft robots are made using highly compliant materials and actuated using pneumatics, electromagnetism and tendons. Because of the low elastic modulus for the materials used to construct soft robots, they are inherently back drivable and compatible for interacting with humans and animals. These same properties, many degrees of freedom and under-actuation, create challenges in the area of modeling and control. We address these challenges by modeling a long, slender, soft robotic swimmer as a visco-elastic rod wherein Lighthill's large-amplitude elongated-body theory is used to represent the nonlinear hydrodynamic forces at a low computational cost. We model the actuation from the swimmer's body using a parameterized internal bending moment. Doing so, we find the optimal locations, size and number of finite fluidic actuators. Finally, we explore the control of the swimmer for best thrust and propulsion efficiency and discuss how to co-optimize the design and control of the soft swimming robot.