Towards Legged Locomotion on Steep Planetary Terrain

Scientific exploration of planetary bodies is an activity well-suited for robots. Unfortunately, the regions that are richer in potential discoveries, such as impact craters, caves, and volcanic terraces, are hard to access with wheeled robots. Recent advances in legged-based approaches have shown the potential of the technology to overcome difficult terrains such as slopes and slippery surfaces. In this work, we focus on locomotion for sandy slopes, comparing standard walking policies with a novel crawling-based gait for quadrupedal robots. We fine-tuned a state-of-the-art locomotion framework and introduced hardware modifications to the robot ANYmal, which enables walking on its knees. Moreover, we integrated a novel metric for stability, the stability margin, in the training process to increase robustness in such conditions. We benchmarked the locomotion policies in simulation and in real-world experiments on a martian soil simulant. Our results show a significant improvement in terms of robustness and stability, especially at higher slope angles beyond 15 degrees.