Robust optimal design of a tail's geometry for stable water-running robots

Stability is important for robots, especially for walking or running robots. The study proposes the optimal biomimetic tail that uses drag force to increase the rolling stability of water-running robots. The tail can reduce the rolling angle by generating a drag force against the direction of rolling motion. For the optimization, the rolling angle is selected by the objective function, while the 9 and 10 Hz operating frequencies of the water-running robot are used for the operating condition. Fillet radius, tail area, and compliances on yaw and roll directions are used for the design parameter. Based on Taguchi methodology, the orthogonal arrays and signal-to-noise ratio are used in the experimental design. As a result, the optimized tail can reduce the rolling fluctuation by 61% while there is no negative force generation along to the running direction. Research on steering by using the tail will be performed in near future.