A soft underwater robot based on functional gradient material is designed to have a streamlined flat head structure and an ellipsoidal tail structure connected by a functional gradient material bulging out the membrane. The cavity inside the flat head expands after inflation, causing the gradient membrane to bulge out directionally, and the cavity in the tail compresses to form a water jet to drive the robot forward. Comparative analysis with the bulging effect of homogeneous membranes is conducted to determine the robot’s optimal motion state. The optimal inflation and deflation times are designed as 3 and 1 s, respectively, with a driving pressure of 15 kPa. Under these conditions, the periodic motion process of the underwater soft robot is verified, achieving an optimal motion speed of 0.446 BL/s—∼79.83% improvement compared to the robot using a homogeneous bulging membrane.
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