Abstract: Different from direct impact damage exerted by limbs of most organisms, mantis shrimps’ appendages can carry out ultra-fast, powerful underwater strikes with cavitation superimposed damage to harvest hard-shelled prey. The power amplification systems and cavitation generation of mantis shrimp have attracted vast attention of researchers. Much effort has been paid to developing mantis shrimp-inspired striking robots; however, none of them are capable of generating cavitation during impacting hard objects yet. In this paper, an underwater striking robot named Shrimpbot was developed to reproduce the cavitation phenomenon when striking hard objects. Shrimpbot incorporates a Latch-Mediated Spring Actuation (LaMSA) to slowly store energy and release it instantaneously. A Diamond-Shaped Four-bar Linkage (DSFL) stretches springs to more effectively store elastic energy by reducing the maximum torque requirement of the motor. This design promised an average power amplification of over 30 times of the motor. Shape optimization and hydrophobic coating on the hammerhead and hand of Shrimpbot helped to reduce the water drag. The accomplished Shrimpbot reached an impact speed of over 12 m/s, at an acceleration of 2?×?103 m/s2, an impact force of more than 1200 N in water, very close to the performance of mantis shrimp. More importantly, cavitation bubbles accompanied with the impacts were observed for the first time in mantis shrimp-inspired robots. Shrimpbot ingeniously employs only one motor to accomplish the striking automatically and repeatedly for practical purposes. Shrimpbot mimics the cavitation generation skills of mantis shrimp, which could facilitate the understanding of its mechanical principles and fluid dynamics of ultra-fast power-amplified systems of mantis shrimp and even those energy storage mechanisms of jumping robots or exoskeleton robots.

Key words: Mantis shrimp , · Biomechanics , · Power amplification , · Cavitation , · Latch-mediated spring actuation