A novel mechanical control system has been proposed for spherical robots to be used as multifunctioning sensor buoys in areas with ambient forces such as winds or currents. The phase-changing pendulum has been specifically designed for Moballs, a self-powered and controllable multifunctioning spherical sensor buoy to be used in the Arctic and Antarctica, or in other solar system planets or moons with atmosphere, such as Mars or Titan. The phase-changing pendulum has been designed to function in different phases: 1) When used as the spherical buoy, the Moball needs to take advantage of external forces such as the wind for its mobility. With no constraints, it could keep the center of mass in the geometric center of the sphere to facilitate the sphere’s movement. 2) However, as soon as the Moball needs to slow down or stop, the sphere’s center of mass can be lowered. 3) Furthermore, the phase-changing pendulum could lean to the sides, thereby changing the direction of the Moball by biasing its center of mass to the corresponding side. The Moballs could take advantage of such a novel phase-changing pendulum to go as fast as possible using the ambient winds, and to stop or steer away when facing hazardous objects or areas (such as the gullies), or when they need to stop in an area of interest in order to perform extensive tests. It is believed that this is the very first time that a pendulum has been suggested to control a spherical structure where both the length and the angle of the pendulum are adjustable in order to control the sphere. 4) Finally, the phase-changing pendulum could also control the sphere in the absence of wind. The spherical sensor buoys or Moballs could use the stored harvested energy (e.g., from sunlight or earlier wind-driven motions) to move the phase-changing pendulum and create torque, and make the spherical sensor buoys initiate rolling with the desired speed and direction. This is especially useful when the spheres need to get close to an object of interest in order to examine it.

(Left) Moball: A self-powered multifunctioning spherical sensor. (Center & right) Moball’s internal mechanical control and energy harvesting system, including its phase-changing pendulum and magnet-weights.
Moreover, since the phase-changing pendulum is connected and lowered from the Moball’s favorite axle, it would make the sphere stop in its favorable orientation so that the integrated sensors, spectrometers, cameras, antennas, etc. could function the best. For example, a spectrometer could be integrated in the lowest area of the outer shell such that when the phase-changing pendulum is lowered and to make the Moball stop, it would touch the ambient surface, either “ground” or “ice,” and could perform its necessary examinations and measurements. The directed antenna could also be integrated in the sphere structure such that when the sphere or Moball stops in its favorable orientation, it would always look up and towards the satellite. The favorable axle could be connected to the outer shell of the sphere using ball bearings. This way, when the outer layer of the sphere rolls, the inner structure will not move. This could be very useful for those systems, such as a camera, inside the Moball that should not move as the spherical sensor buoy rolls around.

The weight-magnets inside the Moball’s tubal axles covered by the solenoids could still be integrated into the Moball’s phase-changing pendulum structure in order to harvest the wind-driven motions when the Moballs are tumbling around. The controlled motion of the magnet-weights could be used to control the Moball’s speed and direction in a fine-tuned manner.

This work was done by Faranak Davoodi of Caltech and Farhooman Davoudi for NASA’s Jet Propulsion Laboratory. For more information, contact This email address is being protected from spambots. You need JavaScript enabled to view it..

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management JPL
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-49011.

Motion Control & Automation Technology Magazine

This article first appeared in the February, 2015 issue of Motion Control & Automation Technology Magazine.

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