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

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 letter introduces a modular three-bar tensegrity robot featuring a customizable payload design. Our tensegrity robot employs a novel Quasi-Direct Drive (QDD) cable actuator with low-stretch polymer cables to achieve accurate proprioception without needing external force or torque sensors. The design allows for on-the-fly stiffness tuning for better environment and payload adaptability. In this letter, we present the robot's design, fabrication, assembly, and experimental results. 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 shape morphing and stiffness tuning capabilities are leveraged in two realistic demonstrations. The presented tensegrity robot is a platform for future advancements in autonomous operation and open-source module design.