DIABLO: A 6-DoF Wheeled Bipedal Robot Composed Entirely of Direct-Drive Joints (2407.21500v3)

Abstract: Wheeled bipedal robots offer the advantages of both wheeled and legged robots, combining the ability to traverse a wide range of terrains and environments with high efficiency. However, the conventional approach in existing wheeled bipedal robots involves motor-driven joints with high-ratio gearboxes. While this approach provides specific benefits, it also presents several challenges, including increased mechanical complexity, efficiency losses, noise, vibrations, and higher maintenance and lubrication requirements. Addressing the aforementioned concerns, we developed a direct-drive wheeled bipedal robot called DIABLO, which eliminates the use of gearboxes entirely. Our robotic system is simplified as a second-order inverted pendulum, and we have designed an LQR-based balance controller to ensure stability. Additionally, we implemented comprehensive motion controller, including yaw, split-angle, height, and roll controllers. Through expriments in simulations and real-world prototype, we have demonstrated that our platform achieves satisfactory performance.

• The paper presents a fully direct-drive joint design that eliminates gearbox inefficiencies and reduces maintenance needs.
• The paper introduces a simplified second-order inverted pendulum model with an LQR controller that maintains balance within 30° deviation.
• The paper validates a comprehensive motion control system through both simulations and real-world tests, ensuring stability on uneven terrains.

Overview of DIABLO: A 6-DoF Wheeled Bipedal Robot with Direct-Drive Joints

The research paper presents DIABLO, a six-degrees-of-freedom (6-DoF) wheeled bipedal robot (WBR) that stands apart by employing direct-drive joints exclusively. This design choice addresses the mechanical complexity, maintenance demands, and inherent issues related to high-ratio gearboxes typically found in such robotic systems. The paper outlines the mechanical and control innovations that enable DIABLO to maintain stability and perform effectively across various terrains.

Key Contributions

The paper delineates three primary contributions:

1. Direct-Drive Joint Design: DIABLO is the first of its kind to incorporate a fully direct-drive joint structure, eliminating gearbox-related inefficiencies and maintenance needs. The mechanical and software integration ensures a robust design, emphasizing sustainability over conventional gear-driven mechanisms.
2. Simplified Dynamics Modeling: The authors propose a novel method for modeling WBR dynamics by simplifying the complex mechanical linkages into a second-order inverted pendulum system. This model serves as the basis for developing a Linear Quadratic Regulator (LQR)-based balance controller. Remarkably, the system achieves reliable balance performance within approximately 30 degrees of deviation from its equilibrium position.
3. Comprehensive Motion Control: The paper also details a comprehensive motion control system that facilitates stable navigation even under challenging conditions, such as maintaining balance when experiencing body tilts and non-horizontal head orientations. Real-world experiments corroborate the robustness of DIABLO's control system in simulations and physical prototypes.

Experimental Validation

The DIABLO platform has undergone rigorous testing both in simulations using a simplified 2D model and real-world scenarios. The simulation environment allowed for extensive fine-tuning of the control parameters, leading to an effective LQR balance controller design. Experimental results show that DIABLO maintains excellent balance during motion, evidenced by the precise control of its pitch and roll angles, as well as stable speed and direction, even on inclined surfaces and uneven terrains.

Implications and Future Work

The implications of this research extend both theoretically and practically. The elimination of gearboxes with direct-drive motors offers a cleaner mechanical design with fewer maintenance requirements—a significant advantage for mobile robotics. The research paves the way for future exploration of direct-drive technology in robotics, particularly for those applications demanding agility and minimal downtime associated with mechanical failures.

The control methodology, based on a simplified dynamic model and capable of supporting diverse terrains and scenarios, highlights potential directions for further research into WBR architectures. This work opens opportunities for enhancing direct-drive systems with integrated whole-body control (WBC) frameworks, improving adaptability across a broader range of applications.

In future developments, the integration of advanced WBC techniques could enhance locomotion capabilities even further, and expanding the design to incorporate additional actuators or sensors could increase the robot's versatility and functional capabilities. The potential for DIABLO in practical applications such as exploration and transportation is evident, and the continued exploration of its capabilities could provide significant benefits across various robotic domains.

Overall, this paper provides a comprehensive insight into an innovative approach to wheeled bipedal robotics, demonstrating the value of direct-drive joints and simplified control models in developing high-performance mobile robotic systems.