Lightweight, inflatable robotic vehicles (rovers) that superficially resemble beach balls and that could be driven by wind and/or electric power are undergoing development. These rovers were conceived for carrying scientific instruments across rocky terrain on Mars, and are intended to move faster, weigh less, and consume less power than do the wheeled robotic vehicles that have been used in planetary exploration until now. Given their resemblance to beach balls in both appearance and function, these rovers have obvious potential for adaptation to terrestrial use, especially as toys.
One previous "beach-ball" rover concept was that of an uncontrolled rover little different from an ordinary beach ball. Another previous concept was that of a spherical balloonlike shell, within which motor-driven weights would be moved along internal diametral tethers to shift the center of gravity to make the shell roll [this concept was described in "'Beach-Ball' Robotic Rovers" (NPO-19272), NASA Tech Briefs, Vol. 19, No. 11, (November 1995), page 83.]
The present concept differs from both previous concepts, though it incorporates some elements of both. The present concept encompasses both single- and double-ball rovers (see Figure 1). A single-ball rover would contain a diametral rod that would serve as an axle. A payload-and-motor-drive assembly could move itself along or across the axle. To enable the ball to roll freely in the wind, the payload mass would be centered in the ball. To stop or prevent rolling, the payload mass would be shifted away from the center, either along or across the axle. With the payload mass hanging down from the axle, another motor drive at one end of the axle could exert torque on the ball to make the ball roll in the absence of wind. Steering could be effected by moving the payload left or right along the axle during rolling or driving.
In a double-ball rover, the balls would be connected by an external axle collinear with their internal axles. The payload-and-motor-drive assembly would be mounted on the external axle. Both balls would be equipped with independent end-of-axle motor drives similar to those of a single-ball rover, for driving or steering. The double-ball rover could roll with the wind or move under its own power, similarly to a single-ball rover. In addition, the external payload mass could be extended far from the external axle to obtain additional torque to climb a rock or a steep slope. A variation of this design has been fabricated and tested with the extendable arm connected to a "slave" wheel that is pulled behind the two drive wheels (see Figure 2).
This work was done by Jack Jones and Andre Yavrouian of Caltech for NASA's Jet Propulsion Laboratory. NPO-20283