DC motor drive
a converter designed to control the speed of DC motors. Controlled rectifiers are generally used and provide a variable DC voltage from a fixed AC voltage. Alternatively, a chopper, or DCâ€“DC converter, can be employed to provide a variable DC voltage from a fixed DC voltage.
A motor drive, in the field of photography, is a powered film transport mechanism. Historically, film loading, advancing, and rewinding were all manually driven functions. The desires of professional photographers for more efficient shooting, particularly in sports and wildlife photography, and the desires of amateur and novice photographers for easier to use cameras both drove the development of automatic film transport. Some early developments were made with clockwork drives, but most development in the field has been in the direction of electrically driven transport.
At first, motor drives were external units that attached to the basic camera body, normally beneath it, with an interface consisting of a physical drive socket and some electrical contacts to signal the drive when to actuate. Beginning in the late 1970s, motor drives began to be integrated into cameras themselves—at first, in compact cameras for the beginner market, and by the 1980s, in amateur-grade and later professional-grade single lens reflex cameras. By the 1990s, the vast majority of 35mm cameras had integral motor drive, and the feature found its way into some medium format cameras as well.