Telemetry - OpenLRS and APM


I have been trying to get telemetry to work with my OpenLRS RX and TX. Been trying out different setups and baud rates but not got it to work.


The transparent serial bridge is working perfectly but when I try to connect the RX to the APM Telemetry port (port 3) I cannot connect via Mission Control. Running a serial monitor I can see traffic - ascii in the beginning saying something like "<startup_mode: ground>" and then binary. Seems to be ok... but not good enough to connect.


I think the problem might be related to bandwidth. OpenLRS supports 750 byte/seconds from the RX to TX. After looking at the documentation and source code I have not figured out how much data MAVLink protocol is configured to send per second.

Does anybody know?



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        • Working with which firmware ?

  • There's now a 1-Watt receiver out from DTF UHF, so all we need now for an open two-way symmetric rc system is mavlink support in main :)

    • I've sent a pull request to Kah for this. 

      He's got lot's of good things todo (apart from mavlink related stuff) but he said that he was going to look over it(it's a clean merge), so theoretically it's quite near mavlink support in main. Or atleast as close as it would ever get I suppose =). The feature is implemented as a separated new telemetry type (selectable via CLI and possible in future from the Configurator (I can't code in python)).

      However the serial port implementation needed to be improved (ie, interrupt driven, like fastserial in APM code), so I guess that's kinda intrusive change, but it works.

      Configurable firmware for openLRS compatible TX/RX systems - openLRSng/openLRSng
      • Thanks Martin for your job. Hope Kah will implement this...

        Ben has made a very very good job to on OpenLRS reliability ie. UltimateLRS for a cheap price.

        So thanks you two for your works on Mavlink, OpenLRS and  telemetry.

    • Yes - Kha has it in his roadmap, but I haven't seen a date when this might be available.

      • While waiting can I suggest to try this : ?

        It's a custom firmware, which allows to use two Hobbyking OrangeRX 1W TX or Flytron OpenLRS 1W TX to create a 1W bidirectionnal link for RC and telemetry (APM).

        It's extremely cheap (2 x $28.95) and works fine. I've flown 12 km away with full 19200 bps APM telemetry.

        • wow Ben, it is great!!!

          Do you mean RF datarate=2 (19200bps)?

          Which Antennas?

          • It's done with a DIY 4 elements yagi ( ) on TX, and a dipole on the plane wing. It ensures a real 19200 bauds end-to-end (of course based on a higher RF rate), which is the minimum necessary for APM / mission planner to work correctly without tweaking.

            Antennas for Ultimate LRS
            • What datarate do you set on the RFM chip? 

              Nice work btw!

              • Thanks, it's 57600 bauds on the RFM chip, it makes a good compromize between range and data rate.

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