Biology is a source of inspiration for many functional aspects of engineered systems. Fish can provide guidance for the design of animal-like robots, which have soft elastic bodies that are a continuum of actuator, sensor, and information processor. Fish respond to minute pressure changes in water, generating thrust and gaining lift from obstacles in the current, altering the shape of body and fins and using sensory nerves in their muscles to control them. Dielectric Elastomer (DE) artificial muscles offer a mechanism for a fish muscle actuator. DE devices have already been shown to outperform natural muscle in terms of active stress, strain, and speed. DE's also have multi-functional capabilities that include actuation, sensing, logic and even energy harvesting, all achievable through appropriate control of charge. But DE actuators must be designed so that they provide enough torque to drive the tail and develop useful forward thrust. In this study bench-top measurements of maximum torque and deflection data for DE actuators have been collected and compared with active torques measured using an instrumented stepper motor driven robotic fish based on the New Zealand Snapper (Pagrus auratus). The rear half of the robot was driven at the mid-section by a stepper motor and a torque sensor interposed between motor and robot body measured swimming torque for a range of speeds and tail amplitudes. The candidate DE actuators were based on a double cone device first described by Choi and co workers, consisting of two convex conical membrane actuators held apart by a stiff central pin. Actuation on one side resulted in rotation of the robotic segment as depicted in figure 1.
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