X2-N: A Transformable Wheel-legged Humanoid Robot with Dual-mode Locomotion and Manipulation

TL;DR

X2-N is a versatile humanoid robot capable of dual-mode locomotion and manipulation, seamlessly transforming between wheel-legged and humanoid forms, with a reinforcement learning control framework enabling complex tasks.

Contribution

The paper introduces X2-N, a high-DoF transformable robot with dual-mode locomotion and manipulation, and a RL-based control framework for unified hybrid operation.

Findings

Demonstrates high locomotion efficiency and terrain adaptability.

Successfully performs dynamic skating, stair climbing, and package delivery.

Achieves stable loco-manipulation in challenging tasks.

Abstract

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.