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.
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