Whleaper: A 10-DOF Flexible Bipedal Wheeled Robot

TL;DR

Whleaper addresses the limited hip mobility of current wheel-legged robots by introducing a 10-DOF bipedal design with 3 hip DOFs per leg, enabling broader postures and obstacle negotiation. It couples a LQR-based sliding balance controller with PPO-based reinforcement learning for walking, validated through simulations and real-world experiments to demonstrate enhanced stability, agility, and flexibility, including lateral walking and obstacle-avoidance sliding. The work details a comprehensive mechanical design, tailored hardware (motors, sensors, communications), and a three-layer software stack, underscored by a distributed simulation platform and policy training in IsaacGym. Future directions include transferring RL to real hardware with MPC and Whole-Body Control to improve precision and reliability in wheel-leg coordination.

Abstract

Wheel-legged robots combine the advantages of both wheeled robots and legged robots, offering versatile locomotion capabilities with excellent stability on challenging terrains and high efficiency on flat surfaces. However, existing wheel-legged robots typically have limited hip joint mobility compared to humans, while hip joint plays a crucial role in locomotion. In this paper, we introduce Whleaper, a novel 10-degree-of-freedom (DOF) bipedal wheeled robot, with 3 DOFs at the hip of each leg. Its humanoid joint design enables adaptable motion in complex scenarios, ensuring stability and flexibility. This paper introduces the details of Whleaper, with a focus on innovative mechanical design, control algorithms and system implementation. Firstly, stability stems from the increased DOFs at the hip, which expand the range of possible postures and improve the robot's foot-ground contact. Secondly, the extra DOFs also augment its mobility. During walking or sliding, more complex movements can be adopted to execute obstacle avoidance tasks. Thirdly, we utilize two control algorithms to implement multimodal motion for walking and sliding. By controlling specific DOFs of the robot, we conducted a series of simulations and practical experiments, demonstrating that a high-DOF hip joint design can effectively enhance the stability and flexibility of wheel-legged robots. Whleaper shows its capability to perform actions such as squatting, obstacle avoidance sliding, and rapid turning in real-world scenarios.

Figures (9)

• Figure 1: Prototype of Whleaper robot and schematic diagram of DOF configuration.
• Figure 2: Schematic diagram of joint space.
• Figure 3: Hardware connection diagram.
• Figure 4: Control system architecture.
• Figure 5: Schematic representation of dynamics model.