System Design of a Tethered Robotic Explorer (TReX) for 3D Mapping of Steep Terrain and Harsh Environments

The use of a tether in mobile robotics provides a method to safely explore steep terrain and harsh environments considered too dangerous for humans and beyond the capability of standard ground rovers. However, there are significant challenges yet to be addressed concerning mobility while under tension, autonomous tether management, and the methods by which an environment is assessed. As an incremental step towards solving these problems, this paper outlines the design and testing of a center-pivoting tether management payload enabling a four-wheeled rover to access and map steep terrain. The chosen design permits a tether to attach and rotate passively near the rover’s center-of-mass in the direction of applied tension. Prior design approaches in tethered climbing robotics are presented for comparison. Tests of our integrated payload and rover, Tethered Robotic Explorer (TReX), show full rotational freedom while under tension on steep terrain, and basic autonomy during flat-ground tether management. Extensions for steepterrain tether management are also discussed. Lastly, a planar lidar fixed to a tether spool is used to demonstrate a 3D mapping capability during a tethered traverse. Using visual odometry to construct local point-cloud maps over short distances, a globally-aligned 3D map is reconstructed using a variant of the Iterative Closest Point (ICP) algorithm.