Multi-Point Repeater Aircraft


Finally getting around to posting about our successful test of our Multi-Point Repeater aircraft last August.

Basically we were able to fly a Quad Mission relaying the mavlink data via our repeater aircraft, itself in an autonomous mission 400ft above. Both the Quad & Fixed wing data were fed through the repeater and were displayed simultaneously on Mission Planner.

The Repeater was made up of a RFD900 (MPSiK V2.5 firmware) and a 3DR 900mhz radio wired directly together. The Rx/Tx and RTS/CTS pins crossed over, powered by a separate battery and mounted on the wing of the fixed wing aircraft.

The Quad & Fixed Wing both had RFD900 with multi-point firmware. The Ground Control Station had a 3DR 900Mhz Radio.

The RDF900s were on the 915-922Mhz frequency range and the 3DR Radios 923-928Mhz. 50 Channels hopping. Both the RFDs and the 3DRs were on separate Net IDs. 

The repeater seemed to work well during the whole mission with the Quad mission completely controlled via Mission Planner.


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  • Hi deadhurricae, (If thats your real name!)

    During this test the repeater aircraft never traveled anymore than 300m from either the quad or the ground station.

    As you can see from the tlog the wireless telemetry connection was around 50% for both aircraft, as expected. Our experienced ground control operator didn't report any noticeable issues during the flight.

  • @Warren Congrats on a successful job! Can you comment at all on any bandwidth issues? I know RFD900s are superior in their range, but how did you find the range of both aircraft using this multi point network and the combination of two radios?

    @Tridge Very interested in what you've mentioned as well, do you have any reference material that you can point me towards to get the twin radio module multi point network set up? 

  • For those who are interested a copy of the Mission Planner tlog can be downloaded here.

    A word of warning. When uploading the missions for the copter & fixed-wing from MP the Waypoint & Loiter Radius from the Copter (10m) was loaded to the fixed-wing! This made for some mighty awesome turns from the fixed-wing traveling at 20m/s!!!

  • @Tridge: You wrote: "The MAVLink forwarding rules in ArduPilot will get the packets through, as long as the two aircraft have different sysids."

    Can you please clarify: If i connect one RF module to telem1 and a second RF module to telem2 on a PixHawk, every received mavlink command on telem1 that has not the SystemID of the PixHawk will be passed through and sent out on telem2? And also vice versa from telem2 to telem1? That would be great!

  • Cheers Randy, Your blog went along way in us achieving this. From our previous conversations you will notice on the MP image that the MavID can only be seen on the Quad and not the Fixed-wing.

  • Developer

    Well done!  Yay, another multi-vehicle flight!  I think this is the first mixed vehicle flight!

  • Hi Tridge,
    Thanks for your comments. Yes, the 50 channels was just left as default, but I was not aware of the limitations in spectrum density in this range you speak of, just 1W EIRP with a minimum of 20 hops. Is it assumed that the full range is used? I'll have to look into that. I chose the two frequency ranges only because it seem a tidy way of doing it.
    Using both telemetry ports in the Pix is a great idea and definitely the way to go. Unfortunately this particular aircraft has a APM2.6 (she flew many years with an APM1)
    I suppose this method is self contained portable unit that could also be used used for ground stations repeaters etc.
  • Developer

    Hi Warren,

    I think using 50 channels over 7MHz may give you a spectral density outside the allowed ACMA rules. I've been experimenting instead with 20 channels over the full 915 to 928 range, but interleaved with each other. That does lead to a small amount of packet loss, but it seems to work.

    I'm also surprised you are directly linking the two radios. Connecting both radios to the pixhawk in the repeater plane should be a lot simpler, and will mean you get telemetry to both aircraft from one link. The MAVLink forwarding rules in ArduPilot will get the packets through, as long as the two aircraft have different sysids.

    Cheers, Tridge

  • Hmm. I thought it is possible to use only one radio on repeater aircraft with SiK multipoint. Such setup can be done without multipoint support in firmware, i guess.

  • Very Cool!

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