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I was looking for a new receiver(think I fried mine) and noticed that some receivers have a 4th line of pins. I've only seen this on receivers where the connections are on the side instead of the top.

What does this 4th line of pins do? Will it work for my plane just the same as a receiver with only three pins? Is there a reason they only appear when the connections are on the side?

Receiver with 4th line of pins

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Modern RC receivers that support PWM/servo output will also support other output modes, which is what the fourth row of pins are usually for.


The extra row of pins you notice on the FlySky FS-iA6B receiver is for extra features of the iBUS signal output. The regular three-high 6-channel PWM outputs are present too.

enter image description here

The FS-iA6B has three different major output modes:

  • PWM: Each channel (1-6) is output on its own servo channel
  • PPM: Each channel (I think either 1-8 or 1-10) is output sequentially on one servo channel in accordance with the CPPM (combined PPM) protocol
    • If enabled, CPPM is output on the PPM/CH1 servo channel
  • iBUS: Each channel is output over a serial UART connection
    • If enabled, serial iBUS is output on the PPM/CH1 servo channel
    • Special auxilary features of the iBUS protocol are available on the 4th row of pins, but these are rarely used. The iBUS signal channel provides all the features usually required fy RC aircraft.

Of the three, iBUS is preferred for use with modern hardware if its supported because of the error-resistant and precision qualities of digital signaling protocols over "analog" ones.

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  • $\begingroup$ so it should work just the same as a receiver with 3 pins? $\endgroup$ – Ceramicmrno0b Nov 6 '20 at 18:26
  • $\begingroup$ Well, what do you mean by that? Which receiver with 3 pins matters a lot! :) $\endgroup$ – ifconfig Nov 6 '20 at 18:27
  • $\begingroup$ This is a link to the receiver I need to replace. $\endgroup$ – Ceramicmrno0b Nov 6 '20 at 18:29
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    $\begingroup$ Oh! So you mean will the PWM outputs work identically? Yes, they will function the same. $\endgroup$ – ifconfig Nov 6 '20 at 18:30
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    $\begingroup$ In case it's not obvious, the main advantage of iBus or CPPM is that you only need one cable when sending the signal to a flight controller. Also, is the 'sens' socket input for telemetry? $\endgroup$ – Robin Bennett Nov 9 '20 at 9:12

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