Autonomous Teamed Exploration of Subterranean Environments using Legged and Aerial Robots

Abstract

This paper presents a novel strategy for autonomous teamed exploration of subterranean environments using legged and aerial robots. Tailored to the fact that subterranean settings, such as cave networks and underground mines, often involve complex, large-scale and multi-branched topologies, while wireless communication within them can be particularly challenging, this work is structured around the synergy of an onboard exploration path planner that allows for resilient long-term autonomy, and a multi-robot coordination framework. The onboard path planner is unified across legged and flying robots and enables navigation in environments with steep slopes, and diverse geometries. When a communication link is available, each robot of the team shares submaps to a centralized location where a multi-robot coordination framework identifies global frontiers of the exploration space to inform each system about where it should re-position to best continue its mission. The strategy is verified through a field deployment inside an underground mine in Switzerland using a legged and a flying robot collectively exploring for 45min, as well as a longer simulation study with three systems.

CERBERUS in the DARPA Subterranean Challenge

“…Responding to this challenge, CERBERUS implemented a resilient autonomy paradigm that uniformly allowed both legged and flying robots to access, explore, map, and search diverse underground environments. At the core of this autonomy solution was the Graph-based exploration path planner (GBPlanner) (5,6). Exploiting a volumetric representation of the environment (7), GBPlanner employed a bifurcated architecture to deliver efficient "local exploration" alongside "global autonomy" over kilometer-sized maps.…”

ArtPlanner: Robust Legged Robot Navigation in the Field

“…We extensively evaluated ArtPlanner during SubT and present results gathered on four legged robots during the Finals, for ArtPlanner and GBPlanner2, the planner used for exploration (Kulkarni et al, 2022). We provide detailed analysis of the challenges faced by ArtPlanner, and how it managed to overcome these adverse conditions.…”

“…Our graph-based exploration planner (Dang et al, 2019;Kulkarni et al, 2022) (GBPlanner2) plans to maximize information gain along the robot path. It operates on a global 20cm voxel-size volumetric map (Oleynikova et al, 2017) which is too sparse to capture the terrain in sufficient detail for legged robot navigation.…”

“…Directly following GBPlanner2's exploration path (Dang et al, 2019;Kulkarni et al, 2022) during the competition would almost certainly have lead to major issues. It did not sufficiently account for traversability characteristics of the terrain, planning directly over high rails shown in Figure 7 .…”

Marsupial Walking-and-Flying Robotic Deployment for Collaborative Exploration of Unknown Environments

“…An overview of the proposed method is illustrated in Figure 3. The method extends our open-sourced Graph-based exploration path planner (GBPlanner) [27] which guided all legged and flying robots of Team CERBERUS [28] in the DARPA Subterranean Challenge. GBPlanner allowed the efficient exploration of complex subterranean environments despite the large-scale, at places highly confined and obstacle-filled, multi-level geometries often involved.…”