SBUS signal issue in ground control

Something appears to be wrong with how my Navio 2 is receiving the SBUS signal from receiver. When I go to radio calibration in ground control the channel monitor dots are all over the place and not moving in correspondence with my stick inputs. I am running servo cable from SBUS port (connected in the right direction) on the receiver to the PPM-SB port on servo rail next to channel 1 with bottom pin being ground. Radio is SBUS paired indicated by purple light on receiver and signal bars from transmitter. Channel monitor does move with stick inputs but in extremely erratic fashion.

FC: Navio 2 w/ RPI3 b+ w/ ADP v 3.5
GC: QGroundControl v.3.32
Transmitter: Radio Link AT9S
Receiver: Radiolink R9DS

Is anyone else experiencing this problem? Is there anyone who knows what might be wrong here?

Hi Paul,

Please follow the steps from this post:

Also, would be good to see the photo of your hardware setup.

Hi @paul.ebbenga,

Was @dmitriy.ershov advice helpful?

The cat/sys/kernel… command is returning a no such file directory found message and I have attached the results of other command below in addition to a picture of my setup. Let me know if there is any further info / pictures I could provide.

Any idea what’s going on or why the command cat /sys/kernel/rcio/rcin/ch2 does nothing? Am I typing it wrong?


I have a working Navio2 system with Futaba sBus.

pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch2
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch2
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch2
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch2
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch2
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch1
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch1
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch1
pi@navio:~ $ cat /sys/kernel/rcio/rcin/ch1
pi@navio:~ $

The “cat” command is working (my Tx is On).

Note: There is a space between cat and /

Update-alternatives result is quite the same except “manual” mode, you have “auto”

pi@navio:~ $ sudo update-alternatives --display arducopter
arducopter - manual mode
link best version is /opt/ardupilot/navio2/arducopter-3.5/bin/arducopter
link currently points to /opt/ardupilot/navio2/arducopter-3.5/bin/arducopter
link arducopter is /usr/bin/arducopter
/opt/ardupilot/navio/arducopter-3.5/bin/arducopter - priority 50
/opt/ardupilot/navio/arducopter-3.5/bin/arducopter-heli - priority 50
/opt/ardupilot/navio2/arducopter-3.5/bin/arducopter - priority 50
/opt/ardupilot/navio2/arducopter-3.5/bin/arducopter-heli - priority 50



Radiolink documentation is clear. As soon as you have the blue-purple light, sBus should work.

Can you verify your R/C Tx is set to ACRO, not HELI.


My transmitter is set to Type: Multirotor … Flight Mode: Normal.

Does mine need to be set to manual mode instead of auto? What difference does this make? Cat command readings below. My ch2 doesn’t seem to move very much but does give some variation when moving sticks.

I should note the these numbers represent stick movements at min and max.

There is a problem somewhere.

Looking at Radiolink R9DS sBus problem (google) it appear sBus period of R9DS could be shorter (13microsecond) than R9D (15 microsecond). If you have a R9D receiver, you should have a try.


I have the RL AT9S tx with the RL R9DS rx. What exactly are you suggesting?

I found some information online that confirms what you are suggesting. Is there any workaround with the R9DS rx with Navio2 or will I need to invest in a R9D rx?

@mlebret do you know if R10D would work? Can’t find any R9D’s with shipping estimates of less than 2 months. Where do you find this period info?

Any advice on the manual v. auto? What does it mean?

It is the flight mode selected. It could be related to your sBus problem as your radio signal is not coherent.

I’m suggesting you should look around you if there are other RC users and have a try with another radio brand. So when sure the Navio is working well, you can choose to buy a R9D receiver (may be working).


I compare R9D and R9DS. On Oscilloscope there is not much one can find without knowing protocol. The only difference is that average packet period with R9D is 13 msec, and with R9DS is 15 ms.
I connect them to spare revo FC and with R9D manual radio calibration went OK below is the video of throttle response (GSC update is slow, so it is choppy)
With R9DS I even could not do manual calibration. Attached is the video of response (no response) during calibration.
I also attached oscilloscope screenshot.

Thank you for your help Marc. Your attachments are not showing up on my end.

It was a quote. Here is the jpg

Not sure, but it could be the R9DS trace (period is 15µs)