A brief report summarizes the design of the lightweight, high-torque wheel drive of a small robotic vehicle used to explore the surface of Mars. Planetary gearing was selected for compactness and high torque capability. The input stages were fitted with ball bearings to survive the cold (down to -100 °C) Martian atmosphere with very light lubrication. To reduce length, a conventional output shaft and its bearing were not chosen; instead, the last-stage planetary shafts were mounted directly on the wheel hubs. A wheel and its gearing are supported by a single "X"-type main ball bearing that takes radial and axial loads as well as offset moments. The balls in this bearing are made of an acetal plastic and are used without lubrication. To reduce weight, hard-anodized, aluminum races were machined directly into the affected structure; after machining, the races were hard-anodized and coated with polytetrafluoroethylene. The inside diameter of the main bearing is large enough to enable the bearing to contain the motor and gear assembly.
This work was done by Donald B. Bickler, Howard J. Eisen, and Angel Olivera of Caltech for NASA's Jet Propulsion Laboratory. No further documentation is available.