SBUS RC Support (FrSky X8R/X4R)?

NAVIO+ is only documented to support CPPM RC input, but Pixhawk and others already support SBUS which supersedes CPPM. Is there a hardware limitation on the NAVIO+ board or would it be possible to use SBUS for RC input?

I’m about to buy some X8R’s as backup receivers because they fit my other requirements (I already have one and want to re-use them later together in chained/16 channel mode), but don’t want to get the SBUS to CPPM converters unless absolutely necessary because they cost over half the price of the receiver itself (20+ euro when the X8R costs about 40 euro).

If the answer is no, then I suppose buying the cheapest possible FrSky multi-protocol receiver with telemetry makes sense. That appears to be the D8R-XP at about 30 euro. Of course that probably makes sense anyway, but I’m also interested in the technical side…

So what are your thought’s on this (Emlid)? Any chance of getting SBUS RC input on NAVIO+? It’s not critical for me, just a niggling limitation. WiFi control is my main objective anyway, but it be nice to know the NAVIO had all the core Pixhawk capabilities covered and I can interchange peripherals/investments can be re-used to full potential.

Tony, unfortunately currently we do not support SBUS due to the way we handle decoding. We are mostly using TFR4 from FrSky, it is compact, FASST compatible and outputs CPPM.

Thanks for the quick response. Afterwards I also found on your “DOCS - PPM RC input” page (which I should have read first) that “For the S.Bus receivers we are preparing a separate driver”.

In case you do find time to give SBUS RC driver development a go, here’s something which may help:

SBUS to CPPM on Arduino

I’ll go ahead with a different receiver or adapter for now then. Maybe play with your example code myself later. So from what I understand then the Navio+ model has no issue with 5v or 3.3v input and it’s just a protocol issue not a hardware limitation.

The PPM input is buffered, so feel free to use 3.3V or 5V.

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I jsut saw navio2 does decode both SBUS/PPM via a microcontroller, Does Navio+ still support PPM only?

Yes and even though it’s software and could be programmed to do anything in theory it’s not feasible to decode SBUS because the CPU time/interrupt speed needed would be too excessive to make it worthwhile, probably not even possible to still run the full ArduPilot software alongside.

With the latest firmware you can already configure the X series FrSky receivers to output CPPM in parallel, so there is no longer a need for a converter with Navio+. And the size of drones used with a Navio (i.e. not a racing drone) won’t lose anything from SBUS reaction time, just extra channels. But then you normally have some kind of telemetry or wireless/mobile link so there are plenty of options for extra command channels.