  Multi-flagellated bacteria utilize the hydrodynamic interaction between their
filamentary tails, known as flagella, to swim and change their swimming
direction in low Reynolds number flow. This interaction, referred to as
bundling and tumbling, is often overlooked in simplified hydrodynamic models
such as Resistive Force Theories (RFT). However, for the development of
efficient and steerable robots inspired by bacteria, it becomes crucial to
exploit this interaction. In this paper, we present the construction of a
macroscopic bio-inspired robot featuring two rigid flagella arranged as
right-handed helices, along with a cylindrical head. By rotating the flagella
in opposite directions, the robot's body can reorient itself through repeatable
and controllable tumbling. To accurately model this bi-flagellated mechanism in
low Reynolds flow, we employ a coupling of rigid body dynamics and the method
of Regularized Stokeslet Segments (RSS). Unlike RFT, RSS takes into account the
hydrodynamic interaction between distant filamentary structures. Furthermore,
we delve into the exploration of the parameter space to optimize the propulsion
and torque of the system. To achieve the desired reorientation of the robot, we
propose a tumble control scheme that involves modulating the rotation direction
and speed of the two flagella. By implementing this scheme, the robot can
effectively reorient itself to attain the desired attitude. Notably, the
overall scheme boasts a simplified design and control as it only requires two
control inputs. With our macroscopic framework serving as a foundation, we
envision the eventual miniaturization of this technology to construct mobile
and controllable micro-scale bacterial robots.
