Adaptive Locomotion for Planetary Exploration Robots

As humanity begins to explore deeper into the universe, the field of robotics has become more crucial than ever. One of the greatest challenges for planetary exploration robots is navigating the variety of surfaces and obstacles that the robot will encounter on its journey. For instance, on Mars, the landscape is rugged and filled with impact craters, cliffs, jagged boulders, and a fine regolith, all of which can cause wheel damage, wheel entrapment, and progressive wheel sinkage over time. Due to the rovers’ limited capability of traversing such rugged terrains, human operators are required to meticulously plan routes, consider safety measures, and navigate the challenges posed by the communication delay associated with sending remote commands to Mars. Over the past two decades, there have been many technological advancements in planetary robotics that have created solutions for these mobility issues. Some notable examples are using reconfigurable wheels to gain more traction on slippery surfaces and using a variety of gaits for legged robots to navigate irregular terrain. However, the potential benefits of merging these technologies remain largely unexplored. A dual-mobility robot, combining features of both wheeled and legged locomotions, could achieve motion on a variety of extraterrestrial surfaces that would be difficult for single-mobility robots. Such a robot could traverse quickly over smooth, hard-packed terrain, adeptly navigate rocky and uneven landscapes, and avoid sinking into deformable soils. This research aims to investigate an adaptive dual-mobility system for quadrupedal robots by combining legged locomotion with reconfigurable, shape-shifting wheels. These wheels could transform from a circular wheel to a shape with a larger ground-contact patch, providing resistance to entrapment or sinkage when walking on soft, deformable surfaces. This work specifically seeks to address the challenges associated with navigating diverse planetary terrains, especially those similar to the surfaces on Mars and the Moon, through the use of multiple locomotion modalities. In order to optimize the design and performance of this dual mobility system, the principles of terramechanics will be incorporated to make sure the system is capable of safely navigating across a variety of soil types and terrain features. The central objectives of this study include enhancing robot mobility, reducing the risk of entrapment, and improving the efficiency of terrain traversability for space exploration robots. During this study, a shape-shifting wheel is 3D modeled, prototyped, and then incorporated into the legs of a quadrupedal robot. Using the Robot Operating System (ROS) framework, the quadruped will have several walking and rolling modes to utilize the shape-shifting wheel integration. An interface will also be developed between the quadruped and the wheels to communicate the physical state of the wheels and additional sensory data. After calibrating and troubleshooting the robot, it will be tested in West Virginia University’s Motion Capture Lab (WVU MoCap) - Gravel and Boulder Pit (Planetary Pit), a Vicon-camera equipped planetary simulation facility at WVU on various terrains resembling the geologic features of Martian and lunar surfaces. Terramechanics simulations will be employed to analyze the performance of the dual-mobility system across these terrains, with an aim of reducing wheel sinkage and increasing traction in soft soils by utilizing the larger ground contact patch of the shape-shifting wheels. The methodology includes iterative design, simulation, and real-world testing to evaluate the system's effectiveness in different environmental conditions. The performance of the dual-mobility system will be evaluated using criteria such as wheel sinkage, slippage, and movement speed. This data will be compared to that of single-mobility systems to determine the effectiveness of a dual-mobility system in planetary exploration applications. The anticipated impact of this research is to significantly enhance the capability of space exploration robots, making them more resilient and suitable for a wider range of planetary terrains. From the findings of our comprehensive literature review performed prior to this study, improvements in mobility and adaptability for complex terrains is a characteristic need for future planetary missions. The findings of this dual-mobility locomotion test are expected to contribute valuable insights into the design and operation of future planetary exploration robots, with implications for both robotic and human exploration missions. Acknowledgments: This study is funded by the NASA West Virginia Space Grant Consortium (WVSGC). The authors would like to thank NASA WVSGC for their financial support and West Virginia University for providing the facilities necessary for this research. Keywords: Space Exploration, Space Operations, Robotics, Dual-Mobility System, Quadrupedal Robots, Shape-Shifting Wheels, Terrain Navigation, Mars, Moon, Terramechanics.