Design and Control of an Agile Robotic Fish With Integrative Biomimetic Mechanisms

Abstract

Flying insects and swimming fishes have high efficiency and high maneuverability in air and water, respectively. Their wings and fins have evolved for many ages to adapt to propelling in the complex environment. In the paper, an integrative biomimetic robotic fish is proposed and developed, which combines the advantages of insect wings and fish fins to achieve a high agility underwater. In the robotic fish, two caudal fins were equipped at the tail of the robotic fish in parallel as the main propulsion mechanism, the opposite flapping of the two caudal fins generates mutually opposing lateral forces during cruising, which leads to a stable and high-performance swimming. In addition, two pectoral fins that mimic the function of insect wings were equipped at two sides of the robotic fish, which enhances the robotic fish maneuverability in vertical plane. Moreover, a central pattern generator (CPG) model was designed to achieve the versatile maneuvering motions, motion switching, and autonomous swimming with an obstacle avoiding ability. The experiments have demonstrated that the robotic fish can swim more stably and efficiently with versatile maneuver motions by taking advantage of the integrative propulsion mechanism. The developed robotic fish have many potential applications for its agility, stable swimming, and low-cost structure.

Torque Analysis of a Flat Reconfigurable Magnetic Coupling Thruster for Marine Renewable Energy Systems Maintenance AUVs

“…Both soft-iron yokes of rotors are made of steel Z8C17 (magnetic stainless steel), with their diameter equal to 62 mm and thickness equivalent to 4.76 mm. The blues lines indicate the two more important magnetic induction lines: the circuit between two magnets in the same part (e.g., magnets (1) and (2)), and a bigger circuit including four magnets, two on each side (e.g., magnets (1), (5), (6) and 2). There are four frames.…”

“…Hence, the attraction and repulsion forces between magnets around the reconfiguration axis y 2 (servomotor axis) are balanced, and there is no torque around this axis. However, the α = 0 • configuration is completely unstable because if α > 0 • (even with a small α) the attraction force between magnets (4) and (8) is greater than the force between magnets (2) and (6), thus there is a torque around axis y 2 , which tends to increase α. In this case, to keep and control α, the servomotor (Figure 1) has to apply a counter torque, which is called restoring torque T Rest in Figure 2 (Γ Rest in [18]), defined by Equation (2).…”

“…Performing the same simulations for others α angles and θ angles, in the operative range θ = [−45 • , 45 • ], it is possible to obtain analytical functions (by regression analysis) to represent T m z and T h z , depending on θ m and θ h , with a good accuracy. Therefore, Equation (4) is extended to θ variations with Equations (5) and (6), which are valid only within this operative range:…”

“…Equations (5) and (6) have analogous forms, which is natural since rotors are identical. If we want to analyze T m z and T h z together according to only one rotation variable (θ m , for example), we could rewrite Equation (6) in function of θ m instead of θ h , leading to…”

“…It is immediate that the propulsion architecture of a vehicle determines its set of possible motion directions as well as influences the ability to control the movement. The first category of propulsion systems offers low maneuverability and the second one is difficult to implement or control [3][4][5][6].…”