Robotic fins mimic stingrays for stable, precise underwater movement

Researchers at the University of California, Riverside, have developed robotic fins that mimic stingray swimming to better understand how these animals achieve stable and precise underwater movement. Stingrays, which dwell near the seabed, use undulatory, wave-like fin motions, while pelagic rays like manta rays flap their fins in smooth, oscillatory motions suited for open water. By testing robotic fins in a water tunnel simulating ocean flow, the team discovered an unexpected "unsteady ground effect": near the seafloor, rays experience negative lift that pulls them downward, unlike birds or airplanes that gain lift near the ground. However, a slight upward tilt of the fins, as observed in real rays, counteracts this negative lift, enabling stable swimming close to the seabed. The study also found that undulatory swimming provides better ground clearance and stability than purely oscillatory fin motions, helping benthic rays avoid collisions with the ocean floor. These insights suggest that the distinct swimming styles of rays are evolutionary adaptations for maintaining