A model radio control is an instrument for remote control of a model . It is usually equipped with two levers to control the power of the engine and steering. There are also models with a wheel and a trigger for model cars. They can be very simple (depth and direction lever and throttle for aircraft) or very complex (changing channels and modes).
Composition of the set
- a transmitter , equipped with a high frequency module, an antenna and a quartz (or 2.4 GHz module is Wi-Fi ).
- one or more receivers depending on the size of the model and safety requirements, equipped with a quartz crystal or a 2.4 GHz receiver on the same frequency as the transmitter, and a receiving antenna.
- a receiver battery that can also be the battery of propulsion.
- of actuators which mechanically transmit to mobile rudders orders received by the receiver.
- in the case of an electric propulsion, a variator / controller , which allows to vary the power of the engine and feed the receiver via the battery propulsion .
The radios emit an FM signal according to two types of modulation . PPM mode, which is cheaper than PCM mode , is generally used on entry-level RC devices. The lower reliability of the PPM mode makes it more suitable for smaller models that are less dangerous than heavier ones. High-end radios offer both modes (PCM and PPM) to offer compatibility with most receivers.
Pulse Position Modulation (PPM) is an FSK- type modulation in which the position of each of the servomotors is encoded by a pulse of variable width. Each frame, of a fixed length, starts with a synchronization pulse. The advantage of this transmission is the simplicity of the electronics needed, which made its success in the early days of radiomodelism. Its main disadvantage is the absence of error detection.
The Pulse Code Modulation (PCM) is a modulation mode type frequency FSK wherein the control of each servomotor is transmitted as an encoded number. Manufacturers each have their own coding system of this number on a variable bit series . JR uses Z-PCM mode ( 10 bits , 512 values ) and S-PCM ( 11 bits , 1024 values ). Futaba uses PCM-1024 and G3 PCM ( 12 bits , 2048 values ). The advantage of PCM coding is to detect transmission errors, which makes it possible to put the servomotorsin a predefined position or to keep them in the last correct position after the loss of the signal: this mode is called ” Fail Safe “, and proves to be interesting from the point of view of the safety, in particular in the helicopters (cut of the gases in case of loss of control of the device).
The abandonment of the frequencies of the order of tens of mega-Hertz in favor of the frequencies of 2.4 GHz has many advantages. First, since the wavelengths associated with this frequency are very small, the length of the antennas of the receivers can be reduced to 3 cm. In addition, the electromagnetic noise especially due to the electric motors, which is between 10 and 100MHz, thus no longer disturbs the nearby receivers.
The authorized aeromodelling frequencies are dependent on states and regions ( 1 ) and ( 2 ).
Notes and references
- ↑ Appendix A7, page 10, in which you will find the bands allocated to radio control in France [ archive ]
- ↑ OJ Decision 2008-0517 of 22 April 2008 setting the technical conditions for the use of frequencies by model radio control systems [ archive ]