Design, modeling, and experimental analysis of the Crawler Unit for inspection in constrained space

Inspections of industrial and civil infrastructures prevent unexpected failures that may lead to loss of life. Although inspection robotics is gaining momentum, most of field operations are still performed by human workers. For inspection robots, the main limiting factors are the low versatility and reliability in dynamic, non-structured and highly complex environments. To tackle these issues, we have designed a modular and self-reconfigurable hybrid platform, which consists of three units: the mobile Main Base and two Crawler Units with docking interfaces. The Crawler Unit operates in constrained environments and narrow spaces, while the Main Base will inspect wide areas and deploy/recover the Crawler Units near/from inspection sites, as in marsupial robots. Docking interfaces will allow the Crawler Units to reconfigure into a snake robot or mobile manipulators. In particular, the Crawler Units consist of four modules connected by three kinematic chains for nine active joints in total. Each module is equipped with half active, half passive tracks for moving. This paper discusses in detail the dynamic model of the Crawler Unit, especially focusing on the definition of effective constraint equations, which closely model the system features avoiding common simplifications. Numerical simulations and physical experiments validate the proposed dynamic model of the Crawler Unit.