Swimming characteristics of a petal-shaped capsule robot with fluid resistance torsion moment-weaken effect

In this paper, a symmetrical, totally 3D printed, Petal-shaped capsule robot (PCR), with fluid resistance torsion moment-weaken effect, is presented. The distribution of fluid dynamic pressure and torsion moment models on the outer surface of the PCR is established, while a constant swimming velocity mathematical model is derived, to describe the relationship between the pressure gradient and the swimming velocity. The higher the fluid dynamic pressure of the PCR is, the smaller the pressure gradient is. The fluid pressure gradient in the liquid-filled environment is the main reason for the full suspension of the PCR. In order to verify the relationship between the pressure gradient, fluid dynamic pressure and the PCR stable swimming velocity, a hand-held magnetic generator, and four novel capsule robot prototypes are developed. The experiments are performed in transparent acrylic pipes of different diameters. The results show that the torsion moment of the four capsule robots, each designed with different eccentricities, gradually decreases as the pipe diameter and eccentricity values increase. Under the same conditions, the rotating speed and constant swimming velocity of capsule robots A, B, C, and D increased successively, obeying the same law as the pressure gradient, which verified the important role of the fluid pressure gradient. The results fully describe the non-contact swimming motion of PCR, under the sole action of fluid dynamic pressure. The research on the characteristics of the pressure gradient poses a certain reference value for further improving the driving performance of capsule robots, specifically laying a foundation regarding their use for examination and medical operation in the non-structural environment of the GI (gastrointestinal) tract.