Frsky bidirectional telemetry implementation

OpenTX would have the UI, via frsky would issue commands to mavToPt which in turn would issue mavlink to the target device

We would have to call a full committee meeting to even discuss that!

Hi Alex,

Happy New Year!

I am trying to understand the physical connections when using your bidirectional telemetry implementation with a Pixhawk 1 and FrSky X8R. Currently, I have the typical FrSky PassThrough setup as described in the Wiki along the the SBUS to RCIN connection for R/C control. This setup works great for Yaapu telemetry and your new mapping feature.

Are you using a bi-directional inverter as in Tridge’s FPort inplementation for F4 based FC boards?

One more question if I may, it seems the FPort implementation needs a receiver that supports the FPort protocol like X4R but your bidirectional telemetry implementation can work with an X8R. Is this correct?

Thanks and Cheers!

I was thinking about a pure lua based GUI.
With @Eric_Stockenstrom’s help we could build a full solution.
A lua based GCS would issue mavlite commands from opentx to the ESP32 via bidirectional frsky, the esp32 would convert mavlite to mavlink and forward to the FC. The FC would inspect the message and relay mavlink to the camera controller.

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Hi Greg, thanks, a Happy New Year to you too!

For bidirectional sport telemetry nothing special is required, if you have the yaapu telemetry script working you are all set.
Current master does not have bidirectional sport support, in order to test the feature you’d need to use my branch.

For fport you have 2 wiring choices:

  1. use RCIN on your board
  2. use a serial port with SERIALn_PROTOCOL = 23

Option 1 is oneway and only allows for RC control, it uses a full software serial implementation and tridge needs to extend it to be two way before we can have telemetry on it.

Option 2 allows both RC + telemetry on a single wire.
It’s two way but right now telemetry is one way only for I haven’t integrated my patches with the fport code.This option requires the very same options/adapters/inverters that are needed by sport, which options to use depend on the board capabilities. For an F4 board for example you still need an inverter ,check here for some examples.

Yes, for fport you need an fport capable receiver like the x4r.

For bidirectional sport X8R works just fine as well as any other sport capable receiver like the R9 series, xsr etc…

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The way you describe it makes it sound easy! (I was just being humorous…)

yaapuAlex Apostoli

@Eric_Stockenstrom I released a dev version of the Lua GCS, it’ here this version can send mavlite command long packets, I’m working on a simpler tool that just sends a specific command every couple seconds, it should make it simpler to work with the new mavlite command_long message.

Nice work Alex ! Impressive. I have some time to get into this again. Could you let me know when the new tool is ready?

Hi Eric,
this should help in testing the command long functionality (17.8 KB)

it sends MAV_CMD_PREFLIGHT_CALIBRATION #241 as a mavlite COMMAND_LONG by using

  • 2 bytes for command id (241)
  • 3 bits for parameters count, (3)
  • 5 bits for confirmation counter, (0)
  • 3 parameters as 4 bytes floats (0, 0, 1)


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Hi Alex, good to hear from you. :slightly_smiling_face:

Thanks for this. I have to admit that I have not gotten down to this properly yet. My intentions are good, but life has been getting in the way!

Hi Eric, lately I’m fighting with bidirectional fport :slight_smile:

…and life tends to get in the way here too :+1:

fport looks like a great idea, and I expect we can’t avoid it.

please any one tell me how can i add some values to SERIAL1_PROTOCOL v in full parameter list

Is it tends to be possible connect r9m to mobile device and control vehicle over qgroundcontrol via telemetry?

No, that’s not possible, this project is about a basic OpenTX based lua GCS.

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Good morning Alex,nice work on your presentation to the AP Developers conference. The video includes all the information I need. Is it possible to get a copy of the slides? Or maybe you could publish the docs?

Hi Eric, thanks,
I realized I never published the video, so here it is

and here’s the link to the slides

let me know if you need lua scripts to test the implementation.



Thanks Alex. Yes I likely will need the lua source, if that’s possible.

sure Eric, sources are on github

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Alex, sorry to ask such a basic question. How do I easily stop your regular lua script from running? Also, when I execute yaapu GCS.lua I get this:


I know its me, but what?

Ok, I seem to have it working.