Most controllers are situated close to the user, e.g. in a ride-on golf buggy, so are controlled by a speed control pot wired directly to the controller.
However some markets, such as Robots and some model locos and boats require remote operation via a radio control system.
4QD controllers are initially aimed at local operator control rather than at the radio control market, so do not have a radio control interface built in.
4QD have an accessory board, the DMR-203, which accepts the signal from a standard radio control receiver and processes it to drive the controller. This turns the controller into what the radio control market know as an ESC – or ‘Electronic Speed Controller’.