An Open Torque-Controlled Modular Robot Architecture for Legged Locomotion Research
This provides an incremental but practical solution for robotics researchers by enabling rapid duplication and experimentation with legged locomotion at low cost.
The authors tackled the problem of creating an accessible, high-performance legged robot for research by developing an open-source, torque-controlled modular system with low-cost actuators and novel foot sensors, resulting in a 2.2 kg quadruped that achieved a maximum dimensionless leg stiffness of 10.8, comparable to a running human, and demonstrated robust motion control.
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.