A dynamic model for tail-actuated robotic fish with drag coefficient adaptation

• A complete dynamic model for a tail-actuated robotic fish is presented.
• Lighthill’s theory is adopted to capture the hydrodynamic force from tail-actuation.
• A computational-efficient scheme is proposed for adapting drag coefficients.
• The model has been validated experimentally with a free-swimming robotic fish.

In this paper we present a dynamic model for a tail-actuated robotic fish by merging rigid-body dynamics with Lighthill’s large-amplitude elongated-body theory. The model is validated with extensive experiments conducted on a robotic fish prototype. We investigate the role of incorporating the body motion in evaluating the tail-generated hydrodynamic force, and show that ignoring the body motion (as often done in the literature) results in significant overestimate of the thrust force and robot speed. By exploiting the strong correlation between the angle of attack and the tail-beat bias, a computationally efficient approach is further proposed to adapt the drag coefficients of the robotic fish, and its effectiveness is supported by experimental results.