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Experimental study of fish-like bodies with passive tail and tunable stiffness

L. Padovani, G. Manduca, D. Paniccia, G. Graziani, R. Piva, C. Lugni

TL;DR

It is shown that changing the frequency of the robot can influence the thrust and power achieved by the fish-like robot, and by using appropriately tuned stiffness, the robot deforms in accordance with the travelling wave mechanism, which has been revealed to be the actual motion of real fish.

Abstract

Scombrid fishes and tuna are efficient swimmers capable of maximizing performance to escape predators and save energy during long journeys. A key aspect in achieving these goals is the flexibility of the tail, which the fish optimizes during swimming. Though, the robotic counterparts, although highly efficient, have partially investigated the importance of flexibility. We have designed and tested a fish-like robotic platform (of 30 cm in length) to quantify performance with a tail made flexible through a torsional spring placed at the peduncle. Body kinematics, forces, and power have been measured and compared with real fish. The platform can vary its frequency between 1 and 3 Hz, reaching self-propulsion conditions with speed over 1 BL/s and Strouhal number in the optimal range. We show that changing the frequency of the robot can influence the thrust and power achieved by the fish-like robot. Furthermore, by using appropriately tuned stiffness, the robot deforms in accordance with the travelling wave mechanism, which has been revealed to be the actual motion of real fish. These findings demonstrate the potential of tuning the stiffness in fish swimming and offer a basis for investigating fish-like flexibility in bio-inspired underwater vehicles.

Experimental study of fish-like bodies with passive tail and tunable stiffness

TL;DR

It is shown that changing the frequency of the robot can influence the thrust and power achieved by the fish-like robot, and by using appropriately tuned stiffness, the robot deforms in accordance with the travelling wave mechanism, which has been revealed to be the actual motion of real fish.

Abstract

Scombrid fishes and tuna are efficient swimmers capable of maximizing performance to escape predators and save energy during long journeys. A key aspect in achieving these goals is the flexibility of the tail, which the fish optimizes during swimming. Though, the robotic counterparts, although highly efficient, have partially investigated the importance of flexibility. We have designed and tested a fish-like robotic platform (of 30 cm in length) to quantify performance with a tail made flexible through a torsional spring placed at the peduncle. Body kinematics, forces, and power have been measured and compared with real fish. The platform can vary its frequency between 1 and 3 Hz, reaching self-propulsion conditions with speed over 1 BL/s and Strouhal number in the optimal range. We show that changing the frequency of the robot can influence the thrust and power achieved by the fish-like robot. Furthermore, by using appropriately tuned stiffness, the robot deforms in accordance with the travelling wave mechanism, which has been revealed to be the actual motion of real fish. These findings demonstrate the potential of tuning the stiffness in fish swimming and offer a basis for investigating fish-like flexibility in bio-inspired underwater vehicles.

Paper Structure

This paper contains 7 sections, 13 equations, 11 figures.

Table of Contents

  1. Introduction
  2. Materials and methods
  3. Results and discussion
  4. Tail stiffness model
  5. Mechanism kinematic analysis
  6. Recirculating channel characterization
  7. Experiments repeatability

Figures (11)

  • Figure 1: CAD section of the fish robot in the left panel to present the internal components of the fish robot and the final prototype realization in the right panel.
  • Figure 2: Robot mechanism: Schematic representation (a), CAD rendering (b), final realization with assembled motor (c).
  • Figure 3: Schematic and realization of the infusion mold used to create the silicone skin of the robotic fish.
  • Figure 4: Control electronics of the fish robot and control station (outside the recirculating channel).
  • Figure 5: Experimental setup for testing the robotic platform. Recirculating channel in the left panel and robot support in the right panel.
  • ...and 6 more figures