Tunabot Flex: a tuna-inspired robot with body flexibility improves high-performance swimming

Area of Science:

• Biomimetics and Robotics
• Fluid Dynamics
• Locomotion

Background:

• Tunas are highly efficient marine swimmers, achieving high speeds through high-frequency movements.
• Current fish-like robots have low speeds and high energy costs compared to tunas.
• The effect of body flexibility on robotic fish performance is not well understood.

Purpose of the Study:

• To investigate the role of body flexibility in high-performance aquatic locomotion.
• To develop a robotic platform, Tunabot Flex, inspired by yellowfin tuna (Thunnus albacares).
• To bridge the performance gap between robotic systems and biological fish swimmers.

Main Methods:

• Designed and tested a single-motor robotic platform, Tunabot Flex (25.5 cm length).
• Varied tail joint flexibility across three configurations to assess performance.
• Measured self-propelled swimming speed, cost of transport (COT), midline kinematics, stride length, and Strouhal number.

Main Results:

• Increased body flexibility improved average swimming speeds by 0.5 body lengths per second.
• The most flexible configuration achieved 4.60 body lengths per second at 8.0 Hz tail beat frequency.
• Minimum COT was reduced by 53%, with the most flexible model's COT being less than an order of magnitude higher than yellowfin tuna.

Conclusions:

• Body flexibility is crucial for enhancing robotic fish swimming speed and energy efficiency.
• Tunabot Flex demonstrates that increased flexibility significantly closes the performance gap with natural tuna.
• This platform serves as a new benchmark for developing high-performance, bio-inspired underwater vehicles.