Helical tail robot to study interactions at low Reynolds number

Some bacteria use helical flagella to self-propel. Their swimming dynamics are relatively well understood, but several aspects remain to be explored.  For instance, it is not clear how swimmers interact with each other especially while swimming in complex media. Instead of using actual living organisms, we have developed  an autonomous swimming robot with a helical tail that operates in the Stokes regime. The robot uses a battery-based power system, with a miniature integrated circuit design which remotely controls the rotational speed of the helical tail.  This torque-free neutrally-buoyant design mimics the swimming strategy of bacteria more closely than other previously used designs. The robot is several centimeters long; hence, we use highly viscous fluids to match the Reynolds number  to be Re ≈ 0.1.  Measurements are conducted  for a range of helical wavelengths, λ, radii, R, lengths, L, and rotation rates, ω. We provide comparisons of the experimental measurements with the predictions of the resistive force theory. Preliminary results of the interaction of the swimmer with walls, free surfaces and other swimmers are shown and discussed.