I. Introduction
A small-sized mobile robot with angled spoke-based wheels called DODO is usually utilized in search and rescue(SAR), inspection, and exploration missions. It can easily access blind spots where heavy equipment or humans cannot enter. In addition, its small body is economically advantageous compared to larger equipment, and can be used flexibly by assembling or modifying multiple robots simultaneously. To perform tasks such as exploring Mars or inspecting and maintaining solar panels on remote desert areas, small-sized mobile robots, including DODO, need to simultaneously locomote granular media and solid ground. Moreover, DODO should overcome the transitional terrain between the granular media, solid ground, and obstacles.