I have submitted a pull request https://github.com/diydrones/ardupilot/pull/520 that adds Spektrum satellite support to the APM2.0/2.5. I know this was possible with the old APM1 and I've seen some people requesting this for the new APM.

I have tested it quite a bit on the desk, but not in flight, since I haven't completed my UAV yet (I wanted this to work first so it will be less of a cable mess). You are free to test it but I take no responsibility if it makes your UAV crash. This is my first contribution to an open source project so I'm not 100% sure about the workflow, but I thought I'd post here as well as adding a pull request, and hope that the right people can test it and verify that it works.

Note that you need some sort of adapter because the satellite is designed for 3.3V, a simple regulator should be enough, since 3.3V is still enough for the AVR to detect as high. I use a fancy adapter that a colleague of mine built, it allows me to connect 2 satellites for diversity and merges it to one output.

Connect a jumper between channel 3 and 4 to enable this mode. It currently does not work with 11 bit frames, and you may experience servo glitches when you have the the USB cable connected. See the pull request for more info.

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Comment by Chris Riccio on August 28, 2013 at 5:00pm

Excuse my relative noobness but what exactly does this "do". I can't seem to tell from what's written. Does it act as the receiver eliminating the need for a much larger receiver and either multiple servo wires or a single servo wire (for PPM). If so, wouldn't just a normal receiver using PPM be just as convenient? 

Comment by Gary McCray on August 28, 2013 at 5:06pm

This is really great.

It has appeared for some time as though the Spektrum satellite receivers ought to be a direct PPM drop in for the APM and I am very happy to see you doing the work to integrate this.

I'd really like to see a simple to construct minimalist interface that would work both with the APM and the PX4.

I'd also like to know if your colleague might have any interest in making his 2 into 1 board available to us all.

Especially on multicopters the ability to have the 2 satellites can be a great safety measure.

Comment by Gary McCray on August 28, 2013 at 5:47pm

Hi Chris, Yes there are a few receivers available that can produce a PPM output and they are in use although they are much less common than normal multiple servo PWM receivers.

The APM can use either a conventional receiver or a PPM receiver and The PX4 can only use a PPM receiver.

But there are advantages to the PPM route including reducing the wire tangle and its associated vibration transmission to the Flight controller.

Control signal reliability and update speed can also be better on the PPM as well.

Futaba and FR-Sky are notable among manufacturers of PPM receivers although I think Graupner does as well.

The advantage Spektrum has is enormous market penetration.

It is probably the most common receiver transmitter combo in the US and their satellite receivers operate on PPM-SUM and are theoretically compatible with our PPM-SUM controller inputs.

Basically with this combo you can skip their main receiver and just use one (or 2) of their satellite receivers instead.

And it will work with your existing Spektrum transmitter.

At least theoretically, this is the first attempt to make it actually work (as far as I know).

Comment by Thomas J Coyle III on August 28, 2013 at 5:55pm

I am presently using a Spektrum PPM satellite receiver with my PX4 FMU/IO. The only issue I had with the PX4 working with the Spektrum satellite receiver is that I had to set the transmitter channel range to +/- 125% to get a 1ms to 2ms PWM range out of the receiver.


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Comment by Gary McCray on August 28, 2013 at 6:17pm

Sorry Tom, I think you might have mentioned this previously and I had forgotten about it.

It seems like a really great option.

Are you using any voltage regulator, dropping resistor or what to make 3.3 volt compatible either direction?

Comment by Thomas J Coyle III on August 28, 2013 at 6:25pm


The PX4 IO board has a special three pin connector for the Spektrum satellite receiver and supplies the satellite with 3.3vdc. No need for a voltage converter:-) Also, the PX4 is a 3.3vdc/5vdc tolerant processor.


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Comment by Gary McCray on August 28, 2013 at 6:41pm

Thank you Tom,

I was thinking of APM, but I do notice SPKT IN on my PX4IO.

I'm definitely going to give this a try.

Currently using 3DR converter and I am sure this will work way better.

As you have already commented it is a power hog and keeps you from connecting via USB only.

Was planning on waiting for Taranis, but this seems a really good solution too.

Comment by Matt on August 28, 2013 at 9:16pm

Wow this is awesome! I think I am going to by a couple of OrangeRX satellite receivers just to have some for other projects, it would be very interesting to to try this, seems as if it would eliminate a couple of grams and some wire mess. Thanks for your contribution! 

Comment by Andy Horka on August 29, 2013 at 8:30am

A single Spektrum satellite on a large carbon octo is a bit scary due to all the shadowing, but I found this and will most likely use it on my current build.




Comment by Sam Kelly on August 29, 2013 at 11:45am

Hi Jimmy, I noticed you didn't mention in your post that the adapter you are using between the Spektrum satellite receiver and the APM is converting the serial output from the receiver to PPM. It is not only a 3V3 regulator/translator. The PX4 reads the receiver's serial data directly, but the APM does not, hence the need for your adapter.


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