Scaling the Turning Rate of a Tuna-Like Robot Performing Frequency-Asymmetric Tail Beating

Turning maneuverability is essential for bio-robots performing underwater tasks such as target searching, environmental exploration, and schooling formation control. Here, we present a single-motor turning mechanism for a tuna-like robot, which is achieved by introducing a frequency asymmetry between the left and right half-strokes of each tail-beat cycle. Experiments are conducted to examine the effects of base frequency and frequency asymmetry on the turning rate. To better control this turning mechanism, we develop a scaling law that predicts the turning rate from the two frequency inputs to within 24% error. The tail of the robot is modelled as a flapping thin airfoil to generate thrust and centripetal forces calculated using linear aerodynamic theory. In addition, the robot’s head is considered a pure drag source. A steady-swimming state is enforced by having the thrust and drag forces equal. This study demonstrates the capability of scaling the propulsive performance of free-swimming bio-robots by modeling them as a combination of an oscillating thin airfoil and a drag source.