LQR-Assisted Whole-Body Control of a Wheeled Bipedal Robot with Kinematic Loops

TL;DR

This paper introduces a hierarchical whole-body control method for a wheeled bipedal robot that integrates full rigid body dynamics, kinematic loop analysis, and LQR-based balancing to enhance robustness and terrain adaptability.

Contribution

It develops a novel control framework that incorporates kinematic loop dynamics and LQR for improved stability and robustness in wheeled bipedal robots.

Findings

Enhanced robustness on rough terrain

Effective control of kinematic loops

Increased stability during curved driving

Abstract

We present a hierarchical whole-body controller leveraging the full rigid body dynamics of the wheeled bipedal robot Ascento. We derive closed-form expressions for the dynamics of its kinematic loops in a way that readily generalizes to more complex systems. The rolling constraint is incorporated using a compact analytic solution based on rotation matrices. The non-minimum phase balancing dynamics are accounted for by including a linear-quadratic regulator as a motion task. Robustness when driving curves is increased by regulating the lean angle as a function of the zero-moment point. The proposed controller is computationally lightweight and significantly extends the rough-terrain capabilities and robustness of the system, as we demonstrate in several experiments.