This paper introduces a novel diameter-varying spherical robot that locomotes by local shell deformation and rolling. The robot is based on a dodecahedron-inspired shell structure equipped with 12 movable outer modules driven by a central screw-driven lifting mechanism. Unlike conventional spherical robots that mainly use the internal mass shift or internal rotating units inside a rigid shell, the proposed robot changes its locally deforming geometry by extending selected outer modules. To investigate the resulting rolling behavior, a physical simulation environment was constructed in Unreal Engine coupled with an external Python controller through OSC-based communication. The physical simulation preserves the essential geometry of the robotic body including control circuits situated in the core part and provides a repeatable platform for observing contact-driven rolling locomotion under time-managed operation. As the initial operational observation of the diameter-varying spherical robot, hardware observations were conducted to examine whether the same deformation-induced rolling principle could be physically realized in the fabricated robot. The paper presents the design of the spherical robot, the locomotion principle, physical simulation environment and the rolling simulation, and the experimental verification of the fabricated robot.
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