Under-actuated tank-like climbing robot with various transitioning capabilities

This paper presents a modular climbing robot connected by two passive compliant joints and featuring an active tail. The objective of this robot is to enable various internal and external transitions which are very challenging tasks for previously developed climbing robots. Realizing the transitions by an using under-actuated system without complex control is another contribution of this research. The robot is driven using a tread-wheel mechanism made of a flat sticky polymer to realize fast and robust climbing. Directional compliant joints are used between the two modules to increase the preload on each front wheel. An active tail is used at the end of the second module to compensate for the negative effects of the compliant joint forces. This combination of directional compliant joints and active tail also allows the robot to perform various internal and external transitions passively. The induced positive preload on the front wheels are analyzed and verified. Three types of internal transition and three types of external transition including a thin wall transition are achieved by the robot prototype. The concept of the directional compliance with the active tail can be adopted to other climbing robots to enhance robustness and mobility.