How does a 2-channel radio work?

[CPW]

Can someone please explain how a 2-channel radio works (like on an RC car)? What I need to know is what the signal looks like. I know it differes with different radios, but how does the electronic board on the car tell the difference between the steering command and the throttle command? Thanks.

 

[audioguru2]

Can someone please explain how a 2-channel radio works (like on an RC car)?

A radio control transmitter sequences through the channels and the receiver follows it.
Each channel's information is a pulse that has a width determined by the control on the transmitter. A servo gets the pulse for its channel from the receiver and moves an amount according to the width of the pulse. 

 

[CPW]

I understand that much, I was mostly wondering how both channels are incorporated into one signal. Thanks for the reply though.

 

[audioguru2]

The transmitter and receiver sequence the channels. The pulse for the 1st channel followed by the pulse for the 2nd channel etc then back to the pulse for the 1st channel again.

 

[CPW]

Is there some kind of "synchronization" pulse to let the receiver know it is starting over again?

I have another question. Is there one pulse for each channel in each sequence or does it repeat the pulse a few times? I was reading this article: http://electronics.howstuffworks.com/rc-toy.htm and it showed that the "synchronization" pulse went four times in a row, and then the pulse for the motor went like 12 times in a row. I'm assuming that's just because they used a cheap little toy to test, right? Normally, you would have this cycle: synchronization pulse, channel 1 pulse, channel 2 pulse, and then it repeats, right?

Thanks for the help.

 

[audioguru2]

Is there some kind of "synchronization" pulse to let the receiver know it is starting over again?

The pulse with a variable width is transmitted for the channels in sequence. A pause is transmitted as a sync pulse to reset the receiver's channel count to zero.

Is there one pulse for each channel in each sequence or does it repeat the pulse a few times? I was reading this article: http://electronics.howstuffworks.com/rc-toy.htm and it showed that the "synchronization" pulse went four times in a row, and then the pulse for the motor went like 12 times in a row. I'm assuming that's just because they used a cheap little toy to test, right? Normally, you would have this cycle: synchronization pulse, channel 1 pulse, channel 2 pulse, and then it repeats, right?

I have never seen the very simple on-off radio control in the article. Proportional signals move each servo to any position that is proportional to the position of the transmitter's joystick and the pulses for the channels are in sequence as you say.

 

[CPW]

I see. So there would be the pulse for each channel in sequence like you said, and then there would be a longer-than-normal pause which tells the receiver it is starting over? Thanks again for your help. I'm finally starting to understand.  ;D

 

[Theatronics]

All correct:
To expand..
In a 4 channel system, both the Tx and RX units are tuned to the same freq. AM/FM doesn't matter Just assume there is a wireless link between the two for now.

Both units also expect to work with a fixed number of channels, in this case 4.

The pulse train would run 4 pulses with a long pause between them to signal the end of the sequence.  Each pulse is between 1 and 2 milliseconds long.  Most RC systems accept that 1.5ms means Centered while 1 and 2 represent the far left and far right positions of a servo. 

The breaks between each pulse and the long break between the sequences can vary depending on the manufacturer.  Some use an edge triggered sync system and the break between the pulses is nothing more than a pulse. 

A simple sequencer takes the pulses and 'routes' them to different outputs on the servo driver.  In fact if you watched the signals coming into the Rx unit and the signals going to out the servos, they would line up.  While Pulse 1 is being routed to Servo 1, The outputs on 2-4 are idle. 

Hope that helps some also...

-Mike

The breaks between each pulse and the long break between the sequences can vary depending on the manufacturer.  Some use an edge triggered sync system and the break beween the pulses is nothing more than a pulse. 

A simple sequencer takes the pulses and 'routes' them to different outputs on the servo driver.  In fact if you watched the signals coming into the Rx unit and the signals going to out the servos, they would line up.  While Pulse 1 is being routed to Servo 1, The outputs on 2-4 are idle. 

Hope that helps some also...

-Mike