Unable to program FrSky SBUS decoder

[Allan Bennett]

I have a FrSky SBUS decoder, but have been unable to get it to work properly using the recommended Frsky SCC Servo Channel Changer.

 

For programming, the SBUS decoder is plugged into the Servo channel on the SCC, and a battery connected to the BAT channel.  I then get a display on the SCC that looks like this photo.  I can navigate between SET and the Set-To channel number using the scroll wheel, and when the Set-To channel number is highlighted, I can change it using the scroll wheel. When I then navigate to SET, as shown in the photo, and press the scroll wheel, the other number on the screen (03 in this case) changes to match the Set-To number.  But the SCC instructions seem to be aimed at programming SBUS servos and its illustrations of the displays don't match my unit, and I can't figure out what I'm supposed to be doing when it comes to using it for programming the SBUS decoder.  All I want is for the SBUS decoder to output PWM to four servos, in response to channels 1, 2, 3, and 4 from an SBUS input from a receiver.

 

At the moment, as a result of lots of almost-random button-pushing I've got the SBUS decoder to sort of operate servos plugged into its channels 1, 2, and 4, but even those don't seem quite right for the servos often vibrate before responding to the Tx stick movement.  I'm using the SBUS output from an S8R receiver for the input to the decoder.

 

Can someone give me a step-by-step instruction how to achieve my desired four PWM outputs from the SBUS decoder please?

 

[Bob Cotsford]

What you are doing sounds correct Allan, I've set them to anything up to ch13 using your exact method.  To step between servo outputs press the button on the decoder, then set the channel to be output as you describe.  What servos are you using it with?  Many analogue servos don't like the higher frame rate that these decoders use (9ms) and will work - after a fashion, but only until they cook themselves.   The oscillation certainly sounds like the behaviour of non digital units.

Edited April 10, 2021 by Bob Cotsford

[Allan Bennett]

Thanks Bob.  For testing I was using a mixture of servos, all analogue.  I didn't realise the decoder output was a higher than normal frame rate.

 

But it's still not clear to me what I'm doing:  In the picture in my original post there's two channel numbers.  I would expect one of them to be the decoder output channel number, and the other to be the SBUS channel number that I want it to respond to -- e.g. I might want channel 2 on the decoder to be channel 6 from my Tx.  But I seem to be able to only toggle to, and change, the number at the bottom of the screen.  So how do I select/change the decoder channel number?

[Ron Gray]

You first select the channel you want to change on the decoder by pressing the button on it (red arrow), the channel will light up on the decoder (green arrow). You then select the channel number you want on the selector, the top number will change to show the number you have selected for the channel on the decoder. Once you have changed them, when you cycle through the channels on the decoder you will see the channel number show on the changer. 

 

If it still doesn't make sense let me know and I'll video it tomorrow morning.

 

[Bob Cotsford]

As Ron said, the programmer displays the current channel (1-16) for the selected decoder output pins (1-4) as indicated by the LED on the decoder (see Ron's pic) on the top line. When you change a channel on the programmer it shows what you will change it to on the bottom line, pressing SET then sends that to the decoder and also displays it on the top 'current channel' line. Pressing the little button Ron pointed to on the decoder steps through the output pin sets 1 to 4.

[Ron Gray]

Clearer explanation than mine Bob, thanks!

[Allan Bennett]

Thanks Ron and Bob, that makes perfect sense now.  I've just tried that out and, as you say, I can select the desired output pin (the top number on the SCC display) using the button on the decoder.  Problem solved!