Analytical modeling and experimental studies of robotic fish turning

Abstract

Turning is one of the most important maneuvers for biological and robotic fish. In our group's prior work, an analytical framework was proposed for modeling the steady turning of fish, given asymmetric, periodic body/tail movement or deformation. However, the approach was not illustrated with simulation or validated with experiments. The contributions of the current paper are three fold. First, an extension to the modeling framework is made with a more rigorous formulation of the force balance equation. Second, we have worked out two examples explicitly, one with an oscillating, rigid tail, and the other with a flexible tail having a uniform curvature, and compared their turning behaviors through numerical results. Third, for model validation purposes, a robotic fish prototype has been developed, with the tail shaft controlled precisely by a servo motor. For a rigid tail, experimental results have confirmed the model prediction that, for the tested range, the steady-state turning radius and turning period decrease with an increasing bias in the tail motion, and that the turning period drops with an increasing tail beat frequency. We have also found that, with a flexible fin attached to the tail shaft, the robot can achieve faster turning with a smaller radius than the case of a rigid fin, and modeling within the same framework is underway to understand this phenomenon.

Robotic Fish Propelled by a Servo Motor and Ionic Polymer-Metal Composite Hybrid Tail

“…One approach is using a single servo to generate asymmetric flapping motion on the tail. Tan et al studied the turning of robotic fish using one precise servo to generate asymmetric flapping [31]. They also found that the robotic fish can achieve better turning performance with a flexible caudal fin, in terms of smaller turning radius, compared to the robotic fish with a rigid caudal fin.…”

Underactuated Robotic Fish Control: Maneuverability and Adaptability Through Proprioceptive Feedback

“…Meurer et al [32] also employed a similar mechanism in a compliant robotic fish using a nonlinear controller, but with a mechanically coupled actuation system and without considering proprioception. On the other hand, classical approaches for steady turning maneuvers involve changing the center of oscillation of the robot's tail, which require large tail deflections to be effective [33,34]. However, the robot presented in this study has relatively small tail segments with space in between them.…”