Preliminary Study On A Robotic Flying Fish Prototype

Many aquatic animals acquire excellent ability to swim underwater or even fly in air through natural evolution.Compared to the artificial underwater robots,the natural aquatic animals are more excellent in mobility,hydrodynamic and aerodynamic performances.Therefore,by learning from the locomotive mechanisms of natural aquatic animals,we can effectively improve the performance of the existing artificial vehicles,or design biomimetic robots.In this thesis,we design a robotic flying fish,which can fold and unfold its pectoral fins,deflect its posterior part of the body,and flap the tail fin in high frequencies.In our study,a robotic flying fish prototype is designed,whose non-standard parts are3D-printed.This robot fish is about 45 cm in length and 890 g in weight.The posterior part of its body are controlled by two servo motors,which can deflect the posterior body vertically and horizontally respectively,therefore achieve pitching and turning operations.The high-frequency flapping of the tail fin is achieved by a high-speed motor,whose rotation is converted into controllable and effective high-frequency flapping by using a set of reduction gears,and a crank link mechanism.We carry out a series of experimental studies on this robotic flying fish,in a small rotating arm basin and a small towing tank,and a high-speed camera is used to record its motions.In the experiments,we study the relationship between the flapping frequency of the tail fin and the swimming speed of the robot fish,by changing the shape and material of the tail fin,as well as the depth of the tail fin immersed in the water.The results show that there is a positive correlation between the flapping frequency and the swimming speed.When the robotic flying fish swims independently in the water,a maximum effective flapping frequency of 20 Hz can achieved,with a maximum speed of 0.3m/s(about 0.5 body length per second).Moreover,to evaluate the required power for underwater swimming and surface taxiing stages of the flying fish,the Computational Fluid Dynamics code STAR-CCM+ is used to carry out numerical simulations for both stages.A direct comparison in power consumption between these two stages is made,which demonstrates the unique ability of the flying fish in further acceleration by taxiing on the water surface before take-off.We also find that the power required to produce high frequency tail flapping is very large,which is a great challenge to electro servos.The current preliminary study on this robotic flying fish prototype can lay a foundation for the further studies on a fully autonomous robotic flying fish,which can perform real multi-modal locomotion,i.e.,swimming in water,flying or gliding in air and pierce through the water surface.