In this letter, we present a novel bi-modal bi-copter robot called Skater, which is adaptable to air and various ground surfaces. Skater consists of a bi-copter moving along its longitudinal direction with two passive wheels on both sides. Using a longitudinally arranged bi-copter as the unified actuation system for both aerial and ground modes, this robot not only keeps a concise and lightweight mechanism but also possesses exceptional terrain traversing capability and strong steering capacity. Moreover, leveraging the vectored thrust characteristic of bi-copters, the Skater can actively generate the centripetal force needed for steering, enabling it to achieve stable movement even on slippery surfaces. Furthermore, we model the comprehensive dynamics of the Skater, analyze its differential flatness, and introduce a controller using nonlinear model predictive control for trajectory tracking. The outstanding performance of the system is verified by extensive real-world experiments and benchmark comparisons.

翻译：本文提出一种名为Skater的新型双模态双旋翼机器人，可适应空中及多种地面环境。Skater由沿纵向运动的两旋翼机构构成，两侧配备被动轮。采用纵向布置的双旋翼作为空中与地面模式的统一驱动系统，该机器人不仅保持结构简洁轻量，还具有卓越的地形穿越能力和强劲转向性能。此外，借助双旋翼的矢量推力特性，Skater能主动生成转向所需的向心力，使其即使在光滑表面也能实现稳定运动。本文进一步建立了Skater的完整动力学模型，分析了其微分平坦特性，并设计了基于非线性模型预测控制的轨迹跟踪控制器。通过大量实际实验与基准对比，验证了该系统的优异性能。