TETRASCEND: the Design, Fabrication and Validation of a Sensorized Soft Climbing Robot

Abstract

Soft climbing robots are promising for inspection tasks in hazardous pipe-like and truss-like environments, as their compliant limbs can adapt well to unforeseen obstacles. However, their deformable and underactuated bodies make contact difficult to control, particularly when contact information is not available. This paper presents TETRASCEND, a four-limbed tendon-driven soft climbing robot with distributed tactile sensing embedded in its arms. Each sensorized arm contains eight force-sensing resistors positioned along the gripping surface, allowing contact location and load distribution to be estimated during grasping and climbing. The sensors were first characterized through loading and unloading experiments, showing repeatable but nonlinear behavior suitable for relative pressure estimation after normalization. A single-arm climbing setup was then used to evaluate grasping across different pipe positions: the center of pressure shifted consistently along the arm as the pipe distance increased, and failure events could be detected by the tactile sensors. Combining tactile sensing with tendon displacement further allowed real pipe contact to be distinguished from free-space arm curling. Finally, the complete robot was validated in a truss-like climbing cage, where the tactile sensors captured sequential contact events during repeated cycles of a climbing gait. These results demonstrate that distributed tactile sensing provides useful information about contact state, grip location, and anchoring stability. Therefore, the TETRASCEND platform is a step toward contact-aware autonomous soft climbing robots