Radio-controlled model: Difference between revisions

Revision as of 17:09, 5 July 2021

Revision as of 17:12, 5 July 2021

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With the electronics revolution<!-- exactly when? -->, single-signal channel circuit design became redundant and instead, radios provided coded signal streams which a [[servomechanism]] could interpret. Each of these streams replaced two of the original 'channels', and, confusingly, the signal streams began to be called 'channels'. So an old on/off 6-channel transmitter which could drive the rudder, elevator and throttle of an aircraft was replaced with a new [[proportional control|proportional]] 3-channel transmitter doing the same job. Controlling all the primary controls of a powered aircraft (rudder, elevator, ailerons and throttle) was known as 'full-house' control. A glider could be 'full-house' with only three channels.

Soon a competitive marketplace emerged, bringing rapid development. By the 1970s the trend for 'full-house' proportional radio control was fully established. Typical radio control systems for radio-controlled models employ [[pulse-width modulation]] (PWM), [[pulse -position modulation]] (PPM) and more recently [[spread spectrum|spread-spectrum]] technology, and actuate the various control surfaces using servomechanisms. These systems made 'proportional control' possible, where the position of the control surface in the model is [[Proportionality (mathematics)|proportional]] to the position of the control stick on the transmitter.

PWM is most commonly used in radio control equipment today, where transmitter controls change the width (duration) of the pulse for that channel between 920 [[microsecond|μs]] and 2120 μs, 1520 μs being the center (neutral) position. The pulse is repeated in a frame of between 10 and 30 [[millisecond]]s in length. Off-the-shelf servos respond directly to [[servo control]] pulse trains of this type using integrated decoder circuits, and in response they actuate a rotating arm or lever on the top of the servo. An [[electric motor]] and reduction [[gear]]box is used to drive the output arm and a variable component such as a resistor "[[potentiometer]]" or tuning capacitor. The variable capacitor or resistor produces an error signal voltage proportional to the output position which is then compared with the position commanded by the input pulse and the motor is driven until a match is obtained. The pulse trains representing the whole set of channels is easily decoded into separate channels at the receiver using very simple circuits such as a [[Counter (digital)|Johnson counter]]. The relative simplicity of this system allows receivers to be small and light, and has been widely used since the early 1970s.