The device essentially consists of a spinning mass inside an outer shell. The shell almost completely covers the mass inside, with only a small round opening allowing the gyroscope to be manually started. The spinning mass is fixed to a thin metal axle, each end of which is trapped in a circular, equatorial groove in the outer shell. A lightweight ring with two notches in it for the ends of the axle rests in the groove. This ring can slip in the groove; it holds the spinning gyroscope centered in the shell, preventing the two from coming into contact (which would slow the gyro down), but still allowing the orientation of the axle to change. Once the gyroscope is spinning, tipping the device causes the gyroscope to precess, with its axle slipping around in the groove in a circular fashion. The groove inside the device is a little wider than the axle; an externally applied torque causes one end of the axle to push against the upper rim of the groove, while the other end pushes against the lower rim of the groove. These two effects combine to make the device work: as the gyroscope precesses in response to an external torque, one end of the axle "rolls" along the top edge of the groove while the other end "rolls" along the bottom edge, speeding up the rotation of the spinning mass.
The acceleration of the gyroscope is best when the precession of the gyroscope is followed by wrist motion, so that an accelerating torque is continually applied. The wrist can be rotated either direction (clockwise or counterclockwise)--the result is always to increase the rotation speed. It takes a while before one finds the "rolling" point, but the gyro will also be accelerated to a smaller extent by the slipping friction which occurs if the wrist is rotated too quickly. Since frictional force is essential for the device's operation, the groove must not be lubricated.
Powerball is a trademarked name for gyroscopic exercise devices produced by Nanosecond (NSD). Later patents for the Powerball device cover its extra features such as revolution counters and gyro-powered LED lights. The light-emitting diodes are powered by a small generator embedded in the gyroscope.
Other Powerball models on the market today are the "Powerball 350Hz Metal" and "NSD SuperPowerBall" (these powerballs are made primarily of metal and have twice the weight of "regular" Powerball models and are more challenging to operate since up to 250Nm of torque is produced); the "Powerball Signature" (featuring a more stable rotor) ; and the "Powerball Screamer" (based on the Powerball 250Hz model, but with 8 holes drilled in the rotor to generate a very loud sound).
Nanosecond's Powerball was the first to feature electronic revolution counters and a generator for light-emitting diodes.
The current records for 250Hz NSD Powerballs are: 16,553rpm peak, 21,228 revolutions in 90 seconds in Strength mode, and a combined 31,816rpm in the Dual category (one Powerball in each hand).
The peak speed record for the (denser) 350Hz "Metal" Powerball is 14,091rpm.
All of the above records are currently held by Akis Kritsinelis from Greece. For other results, see the official NSD Scoreboard