Building a force-free/torque-free robotic bacterial model

The Trinity-Centre collaboration experimentally calibrates numerical models for use as a non-invasive probe to extract forces and torques on bacteria moving near a boundary. Low Reynolds number macroscopic models provide precision data for these calibrations as opposed to biological observations with large uncertainties. Our previous experiments measured forces and torques as a function of boundary distance for helices, cylinders, and spheres, so that we could accurately model bacilli and cocci bacteria such as Escherichia coli, Pseudomonas aeruginosa, and Rhodobacter sphaeroides. However, our experiments have considered each model body part separately. We have now created a simplified model of a rod-shaped bacterium with a counterrotating a cylindrical body and helical flagellum. We measure the axial force and torque and use feedback control to adjust the rotation rates and translation speed to ensure forces and torques on the model are approximately zero. We can thereby create a force-free/torque-free swimmer with the goal of measuring the free-swimming speed as a function of boundary distance.