An Open Torque-Controlled Modular Robot Architecture for Legged Locomotion Research

TL;DR

This paper introduces an open-source, low-cost quadruped robot with torque-controlled actuators and novel sensors, capable of complex, robust locomotion, and provides detailed characterization and control strategies for legged robotics research.

Contribution

It presents a modular, open-source quadruped robot with innovative contact sensors and impedance control, enabling advanced locomotion research and rapid dissemination.

Findings

Achieved a maximum leg stiffness comparable to a running human.

Demonstrated robust complex motion control with environmental uncertainty.

Characterized impedance at the foot in static and dynamic scenarios.

Abstract

We present a new open-source torque-controlled legged robot system, with a low-cost and low-complexity actuator module at its core. It consists of a high-torque brushless DC motor and a low-gear-ratio transmission suitable for impedance and force control. We also present a novel foot contact sensor suitable for legged locomotion with hard impacts. A 2.2 kg quadruped robot with a large range of motion is assembled from eight identical actuator modules and four lower legs with foot contact sensors. Leveraging standard plastic 3D printing and off-the-shelf parts results in a lightweight and inexpensive robot, allowing for rapid distribution and duplication within the research community. We systematically characterize the achieved impedance at the foot in both static and dynamic scenarios, and measure a maximum dimensionless leg stiffness of 10.8 without active damping, which is comparable to the leg stiffness of a running human. Finally, to demonstrate the capabilities of the quadruped, we present a novel controller which combines feedforward contact forces computed from a kino-dynamic optimizer with impedance control of the center of mass and base orientation. The controller can regulate complex motions while being robust to environmental uncertainty.