Slight confusion over ppm limitations

Hi guys,

Hope someone can clarify this for me… I’ve tried to find the answer but I can’t seem to find anything specifically confirming it will work how I want.

I am looking to buy a pixhawk for a project. I have 16ch PPM coming from the Rx, but I don’t require the pixhawk to do anything more than use the first 8 channels, it doesn’t even need to pass through the rest.

So while I can indeed find that the pixhawk seems to be limited to 8ch ppm, and only does 16ch in sbus, unfortunately sbus isn’t currently an option for me. What I would like to know (and am struggling to find the answer to) is whether it will still accept the 16ch ppm stream and simply use the first 8 channels.

Otherwise the only solution I can see is to plug the 16ch ppm into something like the rmilec pwm/ppm/sbus convertor and then feed the converted 16ch sbus output to the pixhawk, or conversely use the first 8 pwm outputs and a ppm encoder to then encode an 8ch stream. Both seem unnecessarily messy if I can just plug the 16ch ppm direct to the pixhawk and have it disregard 9-16.

Thanks for any input, or even a push in the right direction.

Anyone care to take a guess lol? Or perhaps suggest a better place to ask?


Isn’t it easier to test ?
I am not sure, I would need to test to see what PPM decoder does with such input.

It would be easier to test, if I had a pixhawk.

Figuring this out was one of the things I wanted to do before investing in a hardware that may not be suitable for my intended project. Looks like I’ll just have to buy it and find out though, I can’t find the info I need anywhere.

I have two 12ch ppm decoders that work perfectly happily with the 16ch stream - they just output the first 12 channels.


If I had time to spare, I’d test it for you.
And yes, I think it will work just fine, but I don’t dare to say so before testing as I don’t know for sure.

Huh… What are the odds of coming across someone with the same questions?

If you can bear with me for a day, I can have the answers your looking for…

Currently, I know you can use an X8R push ch9-16 over Sbus & use ch1-8 PWM out thru the receiver, traditionally. Also an L9R pushes ch1-12 PPM over Sbus, I think this is by default. I’m running the L9R, right now to a Pixhawk running ver. 3.1.2??? maybe 3.0.2 anyway it’s 3... with no issues…

I think a 16ch ppm summed signal over Sbus would still be valid it would simply ignore any headers above 8, however there are some parameters for RC_IN9-14 would lead me to believe they either plan to expand Arducopters channels or already do in Beta. Of course talking about what APM/3DR are “planning” on doing is similar getting the beans above the frank. We’ve all done it, & learned a very valuable lesson from it!!!