Bacteria-inspired Bi-flagellated Soft Robot with Bundling and Tumbling Behavior

Inspired by bacteria, we present a soft macroscopic robot with two flexible helical flagella that can control its swimming speed and direction at low Reynolds number with two scalar control inputs. A physics-based computational tool, inspired by algorithms used in animation by the computer graphics community, is developed to simulate the robot's motion. Since the discovery of bacterial locomotion, the motility of bacterial flagella has inspired robotic developments under viscous fluid. Our framework introduces a silicone-based design and fabrication strategy using off-the-shelf materials and a feedback control scheme for a constant speed actuation. We investigate two modes of locomotion: bundling and tumbling, which grant the bacteria directional stability and changeable orientation. This work uses the discrete differential geometry-based Discrete Elastic Rod (DER) method to model the flagella as Kirchhoff's elastic rods. DER is coupled with the Regularized Stokeslet Segments method for the hydrodynamics and a contact model due to Spillman and Teschner for a physically accurate simulation of the bi-flagellated soft robot. We present the emergent bundling and tumbling on our macroscopic bacterial robot and compare them with simulation results. As an advance in helical flagella, we propose a simple way of achieving non-reciprocal motion to overcome the constraint set by Scallop's theorem. We expect our framework to encourage more study on the mobility of microscopic flagella robots for the in-vivo operation such as drug delivery.