A reduction drive is a mechanical device to shift rotational velocity. A planetary reduction drive is a small scale version using ball bearings within an epicyclic arrangement rather than toothed gears.
Reduction drives are found in engines of all types to increase the quantity of torque per revolution of a shaft: the gearbox of any car is a ubiquitous exemplory case of a reduction drive. Common household uses are washing machines, food blenders and window-winders. Decrease drives are also planetary gearbox utilized to diminish the rotational rate of an input shaft to an appropriate output speed. Reduction drives can be a gear train design or belt driven.
Planetary reduction drives are typically attached between the shaft of the adjustable capacitor and the tuning knob of any radio, to allow great adjustments of the tuning capacitor with simple movements of the knob. Planetary drives are used in this situation in order to avoid “backlash”, which makes tuning simpler. If the capacitor drive has backlash, when one efforts to listen in a station, the tuning knob will feel sloppy and it will be hard to execute small adjustments. Gear-drives can be made to have no backlash 
by using split gears and spring tension however the shaft bearings have to be very precise.
