How RC (Radio Controlled) commands work

[efron]

Hi Dave,

I would propose to make an eevideo about RC commands and how they are transmitted towards the receiver.

Also how is made the detection of a 4-channel radio command (yes I know it's something about the carrier frequency and multiplexers but ... don't know much more about how all this behaves dynamically to give the final results).

I understand this is more or less standardized now and that it would be a good subjet for discussion, at least from theory point of view.

Thanks in advance,

[Ferroto]

RC commands?

[efron]

RC commands meant to be Radio Controlled orders or commands (i can't find more synonyms for the moment),

e.g. when you push up the throttle in an RC emitter so that the receiver converts that to more power in a remote-controlled motor or servo.

[Ferroto]

I doubt that RC cars would use a standard communication protocal. Maby a standard broadcast frequency due to regulations but not a standard communication protocal. It will be different for all devices and you'll have to reverse engineer it.

[ejeffrey]

I think they are standardized, at least in the hobbyist grade equipment.  For cheap kids toys, probably not so much.

FWIW, back when I was a kid I discovered that my cheap toy remote controlled car used the same frequency band as my cheap toy walkie-talkie.  It was a simple AM protocol.  There was one pair of tones for forward/backward and another pair of tones for left/right.  I learned to whistle the forward/backward commands so I could 'voice control'  (via my walkie-talkie .  Sadly I was never able to whistle two tones at once to turn...

[Ferroto]

Reminds me of how telecoms used to use tone based commands and you could get free long distance by using certian tones which could be produced with a captain crunch whistle. Its also possible that it used FSK (frequency shift keying) where one tone represented a 0 and the other tone represented a 1.

[Baliszoft]

In pro and semi pro RC systems the servos and speedos (motor speed/direction controllers) are commanded by 5v pwm signals. Only three wires are used, two for power supply and one for signal. Where high loads are used, there are additional power supply lines, but their control is the same. The receiver is generating these signals (according to the settings on the transmitter), you can plug as many servos/speedos/etc, into the receiver as many channels the system has. With cars two channels are enough, one for steering and one for throttle/brake.

The method for transmitting the radio signal itself may be different on the am and fm bands, nowadays (for 4-5 years now) a digital method is used on 2.4ghz (for all radios), but the protocol may be different for each manufacturer.