A high-frequency oscillating tensegrity robotic fish with wide-ranging online body stiffness adjustability

Abstract

Body and/or caudal fin (BCF) fish mainly use their body and tail fin as propulsors, and tune their stiffness during swimming to enable rapid and efficient locomotion. However, current variable-stiffness biomimetic robotic fish with high-frequency actuation mainly focuses on the effect of tail fin stiffness. In this paper, we develop a free-swimming tensegrity robotic fish with multi-tensegrity joints, to experimentally study the effect of online body stiffness variation in fish-like swimming with high actuation frequency. We detail its remote high-frequency driving mechanism and fast stiffness adjustment system. We validate the wide-range and fast stiffness adjustment for the tensegrity joint. The robotic fish can dynamically alter various body stiffness distributions online by changing its joints’ stiffness. The experimental results illustrate the nonlinear and dramatic effects of the driving frequency, body stiffness, and swimming state. The ability to adjust body stiffness online in swimming is demonstrated, enabling large range and fast changes in swimming speed and thrust. Compared to other biomimetic robotic fish, the tensegrity robotic fish’s swimming performance is at an upper-middle level, and its variable stiffness ability is outstanding. This work offers valuable insights for the future optimization online of the swimming process in biomimetic fish design.