An innovative underdriven multi-degree-of-freedom sea turtle hydrofoil design

Abstract This study presents a new design for a multi-degree-of-freedom underdriven mechanism. The aim is to achieve efficient bionic motion of a sea turtle hydrofoil with multi-degrees-of-freedom using a single drive source. The design focuses on the kinematic characteristics of the hydrofoil. The design and modeling of the bionic hydrofoil are completed by accurately extracting and fitting the contours of the leading and trailing edges of the sea turtle hydrofoil. The article presents a detailed data analysis of the motion performance of the bionic hydrofoil through pool experiments combined with CCD camera shots. The experimental results reveal that the underdriven bionic hydrofoil moves at a frequency of 0.5 Hz. The correlation coefficients of the waving and rotation angles between the sea turtle hydrofoil and the bionic hydrofoil in the underwater experiments exceed 0.95. The total integral area ratio of the waving angle change curve and rotation angle change curve is more than 0.9. It is demonstrated that the new drive scheme proposed in this paper can realize a single actuator to control the motion of a sea turtle in three degrees of freedom. Breaking away from the traditional paradigm of independent multi-motor drives, the realization of “input-output” motion mapping through mechanical design is of great significance for the complexity reduction of robot control systems.