Scaling of RoboBall: A Parametric Robot Family for Crater Exploration

Non-conventional robotic rovers have gained traction over the past several decades as traditional designs continue to struggle with steep crater edges and other extreme lunar terrain. One particular paradigm of interest in non-traditional rovers in recent years has been inflatable, pendulum-driven spherical robots. Previously, a 2 ft. (0.61 m) diameter spherical robot named “RoboBall II” was built and tested as an alternative rover proof-of-concept. Compared to legacy rover designs, this robot possesses several advantages, including environmental protection, robust operating orientations, and generous descent angle. Despite this, RoboBall II's relatively small size introduced many new challenges, including a lack of payload space. As such, RoboBall II's intended use is primarily as a research testbed and reconnaissance platform. RoboBall III, as a 6 ft. (1.8 m) diameter ball, addresses these challenges. With a 6 in. (0.15 m) diameter hollow annular region as the driveshaft, payloads akin to NASA's CubeSats in size could be fitted to the system for exploration or reconnaissance tasks, allowing RoboBall III to physically interact with its surroundings. However, with scaling comes many challenges. This article will discuss the effects of scaling on slope climbing performance, overall mass, component power requirements, and construction methods from RoboBall II to RoboBall III. Shortcomings between predictive models or derivations and practicality when physically building a robot of this class will be highlighted. These results will be utilized to optimize future RoboBall designs.