Hello. I would like to make a technical question. I believe this place in suitable.

My R/C Tx is operating in PCM mode, which is a digital communication scheme. The PCM modulated signal is received by the R/C Rx which converts it to pulse width modulated (PWM) pulses that get sent to the FC. Then the FC "enriches" this signal in various ways and sends it to the ESC's. The ESC's based on this signal are transferring the high current from the power source to the brushless motors in PWM "style".

I wanted to check whether what i just stated is true. I didn't expand too much. First i just want to see whether these basic rules apply in a typical PCM R/C multicopter setup. As far as i'm concerned most of it should be right. But i have doubts. If there's something wrong where is the mistake exactly and if you just don't understand what i'm saying then please post your opinion on how these signals operate (only serious opinions please. i require absolute precision here).

Could someone please share knowledge and enlighten me?

Thank in advance!

RX to FC can be either PWM, CPPM/S.Bus/PPM Sum, or Spektrum DSM. I have a Pixhawk that takes either CPPM/S.Bus/PPM Sum, or Spektrum DSM. My APM takes either PWM or CPPM, and my CC3D takes either PWM, CPPM, or Spektrum DSM

FC to ESC is PWM.

ESC to Motor is functionally a 3 phase AC sine wave. This explains why you can reverse the motor direction by swapping any two motor leads.

Yes, this is almost what i wanted. I was right. But, one more detail. The PCM / CPPM / SBUS etc. decoding is done on the R/C Rx right?

Originally Posted by Rc3Falc0n

Yes, this is almost what i wanted. I was right. But, one more detail. The PCM / CPPM / SBUS etc. decoding is done on the R/C Rx right?

Actually the PCM to CPPM/S.Bus ENCODING is done in the RX.

The same would apply if you were using a contemporary 2.4gHz PPM system. The individual PPM channel data is encoded into a single CPPM/S.Bus data stream which is then decoded by the FC.

Just out of curiousity, what transmitter are you using?

I'm using the Turnigy 9x.

Wait a sec. Suppose the R/C is using PCM, as my Turnigy 9x is configured to do so now.

So the R/C Tx encodes the signal as PCM. This PCM is received and decoded (and everything else) by the R/C Rx.

What comes out from the R/C Rx is an analog PWM signal that gets sent to the FC.

Do you agree in this setup?

Edit* The APM FC is configured to understand PWM input pulses.

I hate to break this to you, but unless you have an old style PCM receiver, you have to set your radio to PPM.

I have TH9X which just happens to be the "original" 9x that your radio is based on. At first I used this radio for flying helis. As part of an experiment, I disabled the heli drive motor, switched the radio to PCM, and then I powered up the heli. The servos went nuts because the PCM signals the radio was transmitting were not compatible with the stock Fly Sky RX.

Back in the day, (I learned to fly in 1990...)AM radios were old technology. FM/ PCM gear was the standard, and everybody was chasing signal resolution. http://www.futabarc.com/faq/faq-pcm1024.html .

Now its 2.4gHz and PPM.

Were some get tangled up is mixing PPM from the radio to the receiver with CPPM from the receiver to the flight controller.

From the TX, PPM refferrs to how the 2.4gHz carrier frequency is modulated. In a contemporary radio the 2.4gHz carrier is modulated by a digital PPM data stream.

At the RX, the transmission is demodulated. The 2.4gHz carrier is discarded and the PPM data stream is decoded or broken up into separate "channels" which are then turned into either separate PWM signals and sent to the FC over multiple wires, or the channel data are encoded into a single CPPM (Combined Pulse Position Modulated)/S.Bus/PPM Sum data stream that is sent to the FC over a signal wire.

Inside the FC the CPPM signal is separated into channel data which is then used to control the aircraft attitude via PWM signals to the ESCs.

At first i chose PCM as an example.

I'm very sorry. I should have mentioned that i use PPM.

I understood what you said and i COMPLETELY agree! Thank you very much!