The concept of gliding robotic fish combines gliding and fin-actuation mechanisms to realize energy-efficient locomotion and high maneuverability, and holds strong promise for mobile sensing in versatile aquatic environments. In this paper we present the modeling and design of a miniature fish-like glider, a key enabling component for gliding robotic fish. The full dynamics of the glider is first derived and then reduced to the sagittal plane, where the lift, drag, and pitch moment coefficients are obtained as linear or quadratic functions of the attack angle based on computational fluid dynamics (CFD) analysis. The model is used to design the glider by accommodating stringent constraints on dimensions yet meeting the desired specification on speed. A fully untethered prototype of underwater glider is developed, with a weight of 4 kg and length of 40 cm. With a net buoyancy of 20 g, it realizes a steady gliding speed of 20 cm/s. The volume and net buoyancy of this glider are less than 10% and 5%, respectively, of those of reported gliders in the literature, and its speed per unit net buoyancy is over 9 times of those other vehicles. Experimental results have shown that the model is able to capture well both the steady glide behavior under different control inputs, and the dynamics during transients.

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.