A Novel Bio-Inspired Fish Robot with Tunable Stiffness Via Particle Jamming
Jack Stonecipher, Allen Gao, Wei Wang
AI summary
Problem
Robotic fish currently lag behind biological fish in swimming performance, and existing variable-stiffness mechanisms often cause morphological deformation or lack full-body integration for free-swimming validation.
Approach
The authors developed a bio-inspired robotic fish with a full-body particle-jamming mechanism that rapidly tunes stiffness via vacuum pressure while preserving its external shape, then tested its swimming performance across varying frequencies and stiffness levels.
Key results
- Achieved 54% variation in flexural rigidity across 0 to –40 kPa vacuum pressures
- Demonstrated that softer bodies maximize velocity and efficiency at low frequencies (1–1.5 Hz)
- Showed that stiffer bodies deliver superior speed and reduced transport cost at high frequencies (2.5–3 Hz)
- Validated rapid, reversible stiffness tuning with negligible morphological change
Why it matters
Highlights stiffness modulation as a critical design strategy for developing adaptive, high-performance bio-inspired robotic swimmers.
Abstract
Fish achieve efficient swimming across varied speeds through active modulation of their body flexibility. To explore the effects of tunable stiffness on swimming perfor- mance, 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 curva- ture 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.