Control Design for a Rideable Animatronic Two-Wheeled Robot with Quadruped Form

Tadashi Sumioka, Kazushi Akimoto, Takuya Tsujimura, Sho Takayanagi, Yuya Horiuchi

In recent years, motorcycle popularity has been declining, particularly among the younger generations. To rekindle interest in motorcycles among this demographic, we developed a rideable two-wheeled robot equipped with four limbs as a future partner mobility concept and intended for use in public events. The character reproduced by this robot carries the protagonist on its back and exhibits a dynamic quadrupedal gait. To maximize the riding experience, we aimed to match the robot's weight and size to the character's specifications while ensuring rider safety and enabling expressive movements of limbs, wrists, ankles, and facial features. However, achieving locomotion solely through limb movement would require excessive motor output and increased limb strength, resulting in higher weight and extremely slow gait, thereby reducing character fidelity. To overcome these challenges, the robot performs its primary locomotion using a self-balancing two-wheeled base, while the limbs provide auxiliary support during mounting and dismounting and move in coordination with the wheeled locomotion speed. This approach enables an animatronic robot capable of intuitive, weight-shift-based control for free and natural movement. In this paper, we focus on a robust selfbalancing control method that maintains stability even during rapid limb movements, as well as a motion control strategy that generates natural quadruped-like behavior.