Design of a Variable Stiffness Quasi-Direct Drive Cable-Actuated Tensegrity Robot

TL;DR

This paper presents a modular tensegrity robot with a novel variable stiffness cable actuator that achieves accurate proprioception and adaptable stiffness control, enhancing deformability and payload versatility.

Contribution

Introduction of a Quasi-Direct Drive cable actuator with low-stretch cables enabling precise length estimation and on-the-fly stiffness tuning in a modular tensegrity robot.

Findings

Cable length estimation error <1%

Variable stiffness control up to 7 times minimum stiffness

Successful experimental validation of design and control

Abstract

Tensegrity robots excel in tasks requiring extreme levels of deformability and robustness. However, there are challenges in state estimation and payload versatility due to their high number of degrees of freedom and unconventional shape. This paper introduces a modular three-bar tensegrity robot featuring a customizable payload design. Our tensegrity robot employs a novel Quasi-Direct Drive (QDD) cable actuator paired with low-stretch polymer cables to achieve accurate proprioception without the need for external force or torque sensors. The design allows for on-the-fly stiffness tuning for better environment and payload adaptability. In this paper, we present the design, fabrication, assembly, and experimental results of the robot. Experimental data demonstrates the high accuracy cable length estimation (<1% error relative to bar length) and variable stiffness control of the cable actuator up to 7 times the minimum stiffness for self support. The presented tensegrity robot serves as a platform for future advancements in autonomous operation and open-source module design.