A Retractable Soft Growing Robot with a Flexible Backbone

Soft-growing robots are emerging with numerous potential applications because of their superior capability of frictionless navigation. However, their success is hindered by their tendency to buckle under the tension required to retract them via inversion. In this paper, we propose a simple and scalable tubular backbone to facilitate retracting the robot body without buckling. With this backbone, compressive forces at the robot's tip are mitigated and a limit is placed on the effective length for retraction during the application of tension. We first present the selection of the backbone and the development of such a retractable soft-growing robot. Along with the characterization of the working principles behind this buckling-free mechanism, success was observed with the use of the backbone in retraction tests. The effects of different parameters such as robot body lengths, air pressures, curvatures, and retraction modes on the performance were also investigated. This backbone approach requires no bulky or in-situ mechatronic components inside the robot body and thus may be used in medical applications which appreciate simple, compact, and in-situ electronic-free designs.