project specification

DRACO

A human-scaled biped robot with liquid cooled visco elastic actuators (VLCA). The VLCAs include visco elastic elements in the drivetrain in order to improve joint position controllability. Liquid cooled Reaction Force Sensing Series Elastic Actuators (RFSEA) are used for the hip and kneejoints, reducing actuation weight while increasing energy efficiency, torque density, impact resistance and position/force controllability. Liquid-cooled Force Sensing Series ElasticActuators (FSEA) drive the pitch ankle joints for ankle flexion/extension control. To increase heat dissipation onthe electric motors, these VLCAs use liquid-cooling motorjackets enabling 2.5x higher continuous torques on all joints compared to conventional electric actuators.

Specifications

Height130 cm
Weight37 kg
DOF10

Overview

The VLCAs include visco elastic elements in the drivetrain in order to improve joint position controllability. Liquid cooled Reaction Force Sensing Series Elastic Actuators (RFSEA) are used for the hip and kneejoints, reducing actuation weight while increasing energy efficiency, torque density, impact resistance and position/force controllability. Liquid-cooled Force Sensing Series ElasticActuators (FSEA) drive the pitch ankle joints for ankle flexion/extension control. To increase heat dissipation onthe electric motors, these VLCAs use liquid-cooling motorjackets enabling 2.5x higher continuous torques on all joints compared to conventional electric actuators.

Mechatronics design

The DRACO biped has a similar range of motion than an adult human regarding leg and hip motions. DRACO has ten actuated DOFs including three for the hip structure, one for the kneeand one for the ankle. Unlike many humanoid robots, it does not have ankle roll actuation. This allows to significantly reduce distal mass and therefore enhance swing speed motion. The hardware has been designed with performance and mechanical safety consideration while reducing it’s overall weight and the riskof overheating motors.

Viscoelastic Liquid Cooled Actuators (VLCA)

VLCAs are used to actuated the robot joints. VLCA is a family of prismatic SEA with avis coelastic material instead of metal springs and active liquid cooling.

References

Presents the mechatronic design of DRACO. Stability and performance of VLCA are studied. OSC and unsupported dynamic balancing via WBC are described. Lastly, a conclusion is described.

Junhyeok Ahn, Donghyun Kim, et al. June, 2019

Introduces the robot hardware and its characteristic features. Explains the control framework consisting of the dynamic locomotion planner, whole-body locomotion controller, and the joint-level position controller.

Junhyeok Ahn, Donghyun Kim, et al. June, 2018

Wevolver 2022