This paper describes a fish-like robot with a deformable outer shell fabricated using a silicone mold. Based on the difference in the contact condition between the serial-link robot and the shell, the fabrication methods are classified into embedded type and skin type. This study analyzes the mechanical properties of embedded and skin-type underwater robots from the viewpoint of material mechanics. A low-torque motor can sufficiently drive the skin-type underwater robot if the friction coefficient and pressure between the skin and the link are appropriately selected. Furthermore, the outer skin of the fish-like robot can be easily fabricated by defoaming in the chamber of a vacuum-packaging machine. Finally, the performance of the skin-type robot in air and underwater was assessed through several experiments.

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