A Novel Bio-Inspired Fish Robot with Tunable Stiffness via Particle Jamming

2026-06-19

AI Summary

This study addresses the challenge of balancing propulsion efficiency and swimming speed in biomimetic robotic fish across varying tail-beat frequencies by proposing a variable-stiffness design based on granular jamming. The mechanism enables rapid modulation of body bending stiffness through vacuum pressure control, achieving significant stiffness changes without altering external shape or volume, and is implemented for the first time in a freely swimming robotic fish. Experimental results demonstrate that in the low-frequency range (1–1.5 Hz), the soft state (0 kPa) yields the highest swimming speed and lowest cost of transport, whereas at high frequencies (2.5–3 Hz), the stiff state (−40 kPa) exhibits superior performance. These findings elucidate the coupling between body stiffness and swimming performance and validate the critical role of active stiffness modulation in enabling adaptive, high-efficiency, and high-speed locomotion.

Abstract

Fish achieve efficient swimming across varied speeds through active modulation of their body flexibility. To explore the effects of tunable stiffness on swimming performance, we present a bio-inspired freely swimming fish robot with a rapidly tunable particle-jamming body. This design enables rapid stiffness adjustments with negligible changes in shape or volume, achieving a 54% variation in flexural rigidity across vacuum pressures of 0 to -40 kPa. We visualize the midline of the oscillating body under both low- and high-stiffness conditions, and the comparison confirms that the body curvature varies with stiffness. We further experimentally evaluate the tunable stiffness body's effects on swimming performance using velocity and cost of transport (CoT) measurements obtained via a motion tracking system. Results show that active stiffness tuning is essential for sustaining efficient and high-speed swimming across beating frequencies of 1-3 Hz. At low frequencies (1-1.5 Hz), a softer body (0 kPa) maximizes velocity and minimizes CoT, whereas at high frequencies (2.5-3 Hz), a stiffer body (-40 kPa) delivers superior velocity and reduced transport cost. These findings highlight stiffness modulation as a key strategy for adaptive and efficient propulsion in bio-inspired robotic swimmers.

Problem

• tunable stiffness
• bio-inspired robot
• swimming performance
• particle jamming
• flexural rigidity

Innovation

• tunable stiffness
• particle jamming
• bio-inspired robot
• swimming performance
• flexural rigidity