Anytime hybrid driving-stepping locomotion planning

Hybrid driving-stepping locomotion is an effective approach for navigating in a variety of environments. Long, sufficiently even distances can be quickly covered by driving while obstacles can be overcome by stepping. Our quadruped robot Momaro, with steerable pairs of wheels located at the end of each of its compliant legs, allows such locomotion. Planning respective paths attracted only little attention so far. We propose a navigation planning method which generates hybrid locomotion paths. The planner chooses driving mode whenever possible and takes into account the detailed robot footprint. If steps are required, the planner includes those. To accelerate planning, steps are planned first as abstract manoeuvres and are expanded afterwards into detailed motion sequences. Our method ensures at all times that the robot stays stable. Experiments show that the proposed planner is capable of providing paths in feasible time, even for challenging terrain.

I. Introduction

Hybrid driving-stepping locomotion enables robots to traverse a wide variety of terrain types. Application domains, such as search and rescue and delivery services, pose considerable navigation challenges for robots due to non-flat grounds. Sufficiently flat terrain can be traversed by driving, which is fast, efficient and safe, regarding the robot stability. However, driving traversability is limited to moderate slopes and height differences and obstacle-free paths. Stepping locomotion requires only adequate footholds and, hence, enables mobility in cases where driving is unfeasible. But stepping is also slower and decreases the robot stability.