Fish-like three-dimensional swimming with an autonomous, multi-fin, and biomimetic robot

Abstract

Fish migrate across considerable distances and exhibit remarkable agility to avoid predators and feed. Fish swimming performance and maneuverability remain unparalleled when compared to robotic systems, partly because previous work has focused on robots and flapping foil systems that are either big and complex, or tethered to external actuators and power sources. By contrast, we present a robot—the Finbot—that combines high degrees of autonomy, maneuverability, and biomimicry with miniature size (160 cm3). Thus, it is well-suited for controlled three-dimensional experiments on fish swimming in confined laboratory test beds. Finbot uses four independently controllable fins and sensory feedback for precise closed-loop underwater locomotion. Different caudal fins can be attached magnetically to reconfigure Finbot for swimming at top speed (122 mm s−1 ≡ 1 BL s−1) or minimal cost of transport (CoT = 8.2) at Strouhal numbers as low as 0.53. We conducted more than 150 experiments with 12 different caudal fins to measure three key characteristics of swimming fish: (i) linear speed-frequency relationships, (ii) U-shaped CoT, and (iii) reverse Kármán wakes (visualized with particle image velocimetry). More fish-like wakes appeared where the CoT was low. By replicating autonomous multi-fin fish-like swimming, Finbot narrows the gap between fish and fish-like robots and can address open questions in aquatic locomotion, such as optimized propulsion for new fish robots, or the hydrodynamic principles governing the energy savings in fish schools.

The role of hydrodynamics in collective motions of fish schools and bioinspired underwater robots

“…In the absence of external control, free-swimming robots have to generate thrust through deformation and thus move more like real fish [37,[176][177][178]. It has also been discovered that tuning flexibility is essential to match the kinematics of fish [177,[179][180][181][182][183]. Future studies that deploy groups of autonomous free-swimming robots may lead to discoveries of metastable schooling configurations that cannot be observed with tethered hydrofoils.…”

Identification of the trade-off between speed and efficiency in undulatory swimming using a bio-inspired robot

“…We can examine how these quantities depend on body kinematics and investigate underlying trade-offs. Robots are used to study and replicate wake patterns and vortices generated by fishes [5][6][7] , achieve high swimming speeds and accelerations 8,9 , test hypotheses about neural network functionality and sensory feedback of fishes [10][11][12][13][14] , identify optimal passive 15 and active body stiffness 16 , and analyse the hydrodynamic advantage of fish schooling [17][18][19] .…”

Analysis of Heading Stability due to Interactions between Pectoral and Caudal Fins in Robotic Boxfish Locomotion

“…Yet, most of the analyses of fin-fin coupling motion interactions are still on the study of both median fins (anal/dorsal fins) and caudal fin. Although pectoral and caudal fins are the two most important propulsors of fish, and the robotic fish that propelled by both pectoral and caudal fins show better locomotor maneuverability [27][28][29][30], the effect of coupling relationship between pectoral and caudal fins on the cruising performance, especially the stability of forward swimming, has not been systematically analyzed. Furthermore, the analysis of interactions between pectoral and caudal fins will not only enable the robotic fish to modulate its swimming stability and thus be suitable for carrying sensors to undertake operational tasks, but also be a theoretical basis for revealing the locomotion mechanism of fish with multi-fins.…”