Tuna-Inspired Experimental Platforms Exploring High-Performance Fish Swimming

Autonomous underwater vehicles perform a growing variety of missions including exploration, surveillance, and defense. Their conventional designs feature rigid hulls and rotary propellers which contrast the flexible bodies and undulatory tails of fish. As a result, fish exhibit exceptional speed, efficiency, and maneuverability often surpassing that of conventional vehicles. This performance difference motivates the design of vehicles taking inspiration from biology. However, a significant gap in performance exists between such bio-inspired vehicles and the high-performance capabilities of fish. Bio-inspired vehicles typically focus on low-speed locomotion with low tail-beat frequencies. The few systems that do achieve high frequencies often remain limited to low speeds. Consequently, current robotic fish are unable to access the high-frequency, high-speed performance space of fish. Furthermore, the energetic costs of most robotic fish exceed those of fish by orders of magnitude while at a fraction of the speed.

Here we design and test robotic fish able to explore the high-performance space of fish with biologically realistic energy efficiencies. Our bio-inspired systems achieve this by modeling the morphology and kinematics of yellowfin tuna (Thunnus albacares), which are open-ocean swimmers with extraordinary speed and endurance. We present five generations of fish robots inspired by tuna and compare our results with data for tuna and a diversity of fish species. These Tunabots are research platforms that improve our understanding of high-performance fish swimming. The fifth generation, Tunabot Flex, demonstrates that body flexibility improves speed and efficiency. Our work provides a new baseline for the development of state-of-the-art underwater vehicles that aim to explore a fish-like, high-performance space and close the gap between robotic systems and fish swimming ability.