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Futaba SBUS to PPM? FrSKY to the rescue!

Posted by Scott Fuller on August 11, 2013 at 7:00pm

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For months now I've been looking for a SBUS to PPM converter for my Futaba Radio. I want to place my Futaba RX out on one wing and my video TX on the other. While surfing FrSKY's page for a SBUS receiver I ran across a SBUS to PPM converter! I've seen plenty of DIY converters but Aloft hobbies had one cheap in the states and ready to go for about $15. 

After reading around in a few forums I was a bit skeptical about it working. After checking things out in Mission Planner things look good! Now I can finally rip the 10 wires out of the wing and narrow it down to three!

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Hopefully this helps other folks looking for a SBUS to PPM converter. I won't miss the rats nest of wire I had before. 

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Comments

  • Willem Oldemans August 12, 2013 at 11:03am

    I didn't look to good for cppm option when ordered my frsky Taranis wit X8R receiver, it only has 16ch sbus and 8x ppm out. I received my sbus<->cppm a few day's ago, works like a charm! and by the way, the Taranis is awsom!

  • Scott Fuller August 12, 2013 at 8:45am

    John, Agreed. Futaba went out of their way to make this their own protocol. It seems the rest of the industry has adopted PPM as the standard leaving Futaba users out. 

    Dror, sometimes going back to the archaic technology is the easiest route. *sarcasm* NASA is going back to capsules after all /sarcasm. I'd love to see the APM speak SBUS natively as I'm heavily invested in SBUS from my sport flying days. Something like move the jumper to output pins 2-3 instead. I've seen patches that allow APM to speak SBUS but that seems more error prone as it's not in the current release. The excitement comes when I can rip a hefty CAT-6 cable out of my plane and replace it with three wires. 

    Greg and FD - Don't know if you guys have seen the TFR8S RX from FrSKY but it's something I've been keeping an eye on...

    http://www.alofthobbies.com/frsky-tfr8-8-channel-fasst-compatible-r...

    You can 'stack' the receivers to give you up to 14 channels. You figure 1-8 would go into the APM and the remaining channels you hook directly into. The other RX I've been look at is the TFRSP that gives you up to 10 channels. 

    http://www.alofthobbies.com/frsky-tfrsp-fasst-cppm.html

  • FD August 12, 2013 at 8:05am

    Hi all, have a look at this Delta-8 Receiver (obviously built on FrSky Hardware): http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=42310

    It is compatible to a lot of protocols, including S-FHSS that my Futaba T8J uses and RSSI and CPPM. Nice.

    There is a thread on RC-Groups if you like to know more: http://www.rcgroups.com/forums/showthread.php?t=1874908

  • Greg August 12, 2013 at 6:44am

    One thing that might be cool with this setup is you might be able to also use the PWM ports for other, non autopilot things. (i.e. 8 channels for autopilot, 8 channels for other things like camera controls, gimbal, undercarriage etc, etc = 16 channels).

    Am I reading the specs correctly? See bullet point 2. (Actually they quote 18 channels, maybe SBUS has an extra 2 channels?)

    http://www.futaba-rc.com/systems/futk8010.html

  • 3D Robotics
    Chris Anderson August 12, 2013 at 6:19am

    patrick: yes

  • Dror Caspi August 12, 2013 at 1:07am
    Furthermore, who said analog isn't easy? Sampling analog voltage is also easy if you have integrated ADCs on your microcontroller.
  • Dror Caspi August 12, 2013 at 1:05am
    Technically, PPM is analog, in the time domain.
  • Developer
    John Arne Birkeland August 12, 2013 at 12:43am

    SBUS is just plain serial data like we use for most communication.

    But Futaba in their infinite wisdom went out of their way to use a custom baud rate and invert the electrical signal, so to make it incompatible with many micro controller serial interfaces, including ours. If not for this, implementing SBUS support in APM would be possible. But as it is, you need external hardware to make it possible.

    As to why we are using PPM instead of I2C or serial. Turns out PPM is dead simple to decode on a micro-controller and uses virtually no resources compared to parsing serial or I2C commands. And there's isn't a single documented case of external PPM signal corruption, so why reinvent the wheel?

    And PPM isn't technically a analog signal. The pulses are fixed at 5V and the pulse width represent the channel value. Making it a time domain signal (PWM), that is easy and accurate to handle on micro-controllers.

  • Dror Caspi August 11, 2013 at 11:58pm
    I am rather amazed to see people so enthusiastic about such an archaic technology as PPM. You see, what you're doing with Sbus to PPM conversion is taking digital information and converting it to an analog, error prone representation.
    Wouldn't it be better if APM could read Sbus directly, or if we converted PPM to I2C or serial?
    Dror
  • patrick74 August 11, 2013 at 11:07pm

    Hello....not a pro of radio equipment....so little question...how the ppm reduce the number of wire...I am guessing it is about sending serial signal in one wire...but this is between APM and the receiver?

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