Locomotion of Soft Robots with Flexible Uni-flagellum in low Reynolds Number Fluid

In nature, more than 90% of the bacteria propel using a single flagellum. The uniflagellar bacterium is comprised of a basal body and a flagellum, with a flexible hook connecting the two. Experimental and numerical observations indicate that the flexibility of the flagellum and its buckling are essential to change the swimming direction of the bacterium. We simulate the locomotion and deformation of the flagellated system in low Reynolds number conditions using a combination of the Discrete Elastic Rods and the Lighthill Slender Body Theory. The simulator shows that the robot is able to follow a prescribed three-dimensional trajectory by simply controlling the angular velocity of the flagellum. Inspired by natural bacterial structure, we fabricate a self-contained robot with a rigid and a motor-actuated elastomeric helical rod - our analog for the flagellum. With a motor, sensors, and a flexible control circuit embedded inside the head, the robot is able to follow a prescribed nonlinear trajectory by flagellum buckling. This robotic system demonstrates how structural instability can be harnessed for control of soft robots. It can also serve as an analog model for the natural bacterium to help us understand the fluid dynamics and biophysics underlying the propulsion of bacteria.