Model-Based Control of a Robotic Fish to Enable 3D Maneuvering Through a Moving Orifice

Three-dimensionally (3D) maneuverable robotic fish are highly desirable due to their ability to explore and survey the underwater environment. Existing depth control mechanisms are typically focused on using either compressed air or a piston to generate changes in volume. However, this often makes the system bulky and therefore impractical for use in small size underwater robots. In this letter, a small and compact 3D maneuverable robotic fish is developed. Instead of using a compressed air tank, the robot is equipped with an on-hoard water electrolyzer that generates gases in the required amount, in order to achieve changes in depth. The fabricated robotic fish demonstrates fast diving and rising performance. A servo motor is used to generate asymmetric flapping motion on the caudal fin for two-dimensional (2D) planar motion. A 3D dynamic model is derived for the fabricated robotic fish. This 3D model is then embedded into a relative velocity framework, to develop a guidance and control scheme that enables the robotic fish to maneuver through underwater orifices. These underwater orifices may be either stationary or moving. Simulations are used to demonstrate the efficacy of the developed algorithm.