Whleaper: A 10-DOF Flexible Bipedal Wheeled Robot

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.

Analysis of Whleaper: A 10-DOF Flexible Bipedal Wheeled Robot

The paper presents the development and analysis of Whleaper, a novel 10-degree-of-freedom (DOF) bipedal wheeled robot designed to enhance the balance between efficiency and versatility in wheel-legged robotics. Whleaper addresses the challenge of integrating increased hip mobility, akin to human anatomical capabilities, allowing it to navigate complex environments with greater stability and flexibility.

Key Contributions

The paper's primary contributions are delineated as follows:

1. Mechanical Design Innovation: Whleaper features a unique 10-DOF architecture, with 3 DOFs at each hip joint. This design aims to mimic human hip functionality, thereby augmenting locomotion adaptability. The mechanical configuration, including the series-parallel hybrid connection and four-bar linkage system, ensures efficient torque transmission and reduced leg inertia.
2. Advanced Control Algorithms: The deployment of Linear Quadratic Regulator (LQR) and Reinforcement Learning (RL) algorithms enables Whleaper to perform complex multimodal locomotion tasks. The use of LQR for stabilizing sliding and RL for adaptive walking and jumping illustrates the robot's maneuverability across different terrains.
3. System Integration and Validation: The researchers constructed a comprehensive system comprising specialized electrical and communication infrastructure, validated through simulations and real-world experiments. This integration highlights the robustness of Whleaper's design in executing tasks such as obstacle avoidance and rapid turns.

Experimental Insights

The experiments substantiate the efficacy of the proposed design. Through a series of simulations and practical implementations, Whleaper demonstrated significant improvements in stability and agility due to its enhanced hip DOFs compared to existing models. The results indicate:

• Stability and Control: Enhanced DOFs allow for superior control over base orientation and angular velocity, effectively stabilizing the robot in dynamic scenarios.
• Agility in Movements: The capability for rapid directional changes without compromising balance, a feat achievable by the addition of hip-roll and hip-yaw motions.
• Flexibility: Demonstrations of human-like actions and adaptive postures underscore the benefits of increased DOFs, facilitating complex maneuvers such as lateral walking and obstacle avoidance sliding.

Implications and Future Directions

The implications of Whleaper's design transcend practical applications in robotics where a balance of efficiency and adaptability is critical. Urban delivery, search and rescue, and personal mobility are potential domains where Whleaper could be effectively employed.

The paper's findings suggest several future research trajectories. Further refining the control algorithms, potentially through the incorporation of Model Predictive Control (MPC) and Whole-Body Control (WBC), could enhance the precision and reliability of the robot under diverse conditions. Bridging the sim-to-real gap remains a considerable challenge that must be tackled to transition these innovations from controlled simulations to real-world applications.

In conclusion, Whleaper represents a significant stride in wheel-legged robotics, offering a blend of humanoid flexibility with mechanical efficiency. By leveraging increased DOFs and sophisticated control strategies, the paper sets a promising precedent for future advancements in versatile robotic locomotion systems.