The planetary reduction drive is based on an old but ingenious design. Based on a system of ball bearings rolling between two surfaces while housed within a rotating bushing, the planetary reduction drive is often used to enhance the fine-tuning control of a variable capacitor.

In most applications, a knob is attached to the planetary drive’s input shaft, a variable capacitor’s shaft is fastened into the planetary drive’s output shaft coupler, a vernier dial is attached to the unit’s optional dial flange, and the unit’s mounting bracket is attached to a stationary housing or cabinet. When the knob is turned through one complete rotation, the vernier dial and the capacitor's shaft rotate one-sixth of a rotation. Thus, a very small change in capacitance does not require extremely fine motor skills on the part of the operator.

Most remarkable is the fact that this "gearing down" is achieved without gears, but through rolling balls. This is an old principle, but one that didn’t really come into its own until modern methods and materials were applied to it. The precision, excellent surface finishes and complex geometries possible with CNC machining, the economy and availability of steel balls held to tolerances on diameter and sphericity that were once impractical, the specific properties of modern alloys and materials, and some refinements of the design have led to our current planetary drive performing dramatically better than any previously manufactured, probably better than the original designer had ever thought possible.

A critical component in the performance of a planetary drive is its "feel". Our current planetary drive has the characteristic silky-smooth feel expected by the end-user when turning a knob on a modern piece of electronic equipment. Compact, reliable, durable, consistent, and economical, there are two standard models of planetary drive available: The BD601, for use with a vernier dial; and the BD602, without the dial flange.