Wheel-legged robots combine the efficiency of wheeled locomotion with the versatility of legged systems, enabling rapid traversal over both continuous and discrete terrains. However, conventional designs typically employ fixed wheels as feet and limited degrees of freedom (DoFs) at the hips, resulting in reduced stability and mobility during legged locomotion compared to humanoids with flat feet. In addition, most existing platforms lack a full upper body with arms, which limits their ability to perform dexterous manipulation tasks. In this letter, we present X2-N, a high-DoF transformable robot with dual-mode locomotion and manipulation. X2-N can operate in both humanoid and wheel-legged forms and transform seamlessly between them through joint reconfiguration. We further propose a reinforcement learning (RL)-based whole-body control framework tailored to this morphology, enabling unified control across hybrid locomotion, transformation, and manipulation. We validate X2-N in a range of challenging locomotion and manipulation tasks, including dynamic skating-like motion, stair climbing and package delivery. Results demonstrate high locomotion efficiency, strong terrain adaptability, and stable loco-manipulation performance of X2-N, highlighting its potential for real-world deployment.

翻译：轮腿机器人结合了轮式运动的高效率与腿式系统的多样性，能够在连续与非连续地形上实现快速穿越。然而，传统设计通常采用固定轮作为足部，且髋关节自由度有限，导致其腿部运动的稳定性与机动性低于使用平足的人形机器人。此外，现有大多数平台缺乏完整的上半身与手臂结构，限制了其执行灵巧操作任务的能力。本文提出X2-N——一种高自由度可变形机器人，具备双模态运动与操作能力。X2-N能以人形与轮腿两种形态工作，并通过关节重构实现在两者间的无缝切换。我们进一步提出一种基于强化学习的全身控制框架，针对该形态设计，实现对混合运动、变形与操作的统一控制。我们在多项具有挑战性的运动与操作任务中验证了X2-N的性能，包括动态滑冰式运动、爬楼梯及包裹递送。实验结果表明，X2-N具有高运动效率、强地形适应性及稳定的运动-操作复合性能，凸显了其在实际场景中的应用潜力。