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ELRS Custom Telemetry

ExpressLRS uses the Crossfire (CRSF) protocol, whose standard telemetry has room for only a few values, mostly aimed at multirotors -- no headspeed, no governor state, no ESC temperature. Rotorflight's custom telemetry sends its own sensors over the same link instead: more than 100 to choose from, up to 40 at once, updated up to 20 times a second.

The radio needs a script to decode the custom frames. The current Lua suites do this themselves:

Radio Decoder
FrSky Ethos The Rotorflight Lua suite's background task.
EdgeTX (colour, 2.11+) RFSuite -- its widgets, or its background decoder.
Older EdgeTX / OpenTX The rf2tlm.lua script from the classic Lua scripts, run as a custom script.

Use ExpressLRS 3.5.5 or later

ELRS before 3.5.5 has a bug that can cause loss of control when telemetry is busy. Update your transmitter module and receiver.

1. Flight controller

On the Receiver tab:

  1. Telemetry: Enable -- on.
  2. Custom Telemetry -- on.
  3. Telemetry Packet Rate -- the same as the ELRS Packet Rate on your transmitter module (e.g. 500 Hz).
  4. Telemetry Packet Ratio -- the same as the ELRS Telem Ratio (e.g. 1:4 → 4). Start at 4; if the radio reports telemetry lost, go higher (up to 16).
  5. Choose the sensors under Telemetry Sensors, then Save.

Let the suite choose

Saving the Telemetry page in the Ethos or EdgeTX suite picks sensors for its dashboards and switches the flight controller to Custom mode for you. There are also presets on the Presets tab.

2. Radio

  1. Set the ELRS module's Packet Rate and Telem Ratio to match step 1.
  2. Install and enable the decoder for your radio (table above). On Ethos, enable the Rotorflight background task; on EdgeTX with RFSuite, either a dashboard widget or the background decoder must be running.
  3. Discover sensors: delete the existing telemetry sensors on the radio, start Discover new, and only then power up the helicopter. Powering up first can leave the sensors in the wrong order.

Troubleshooting

Problem Try
Telemetry lost warnings Raise the telemetry ratio (on both module and flight controller).
A sensor never appears, and others stop updating The suite doesn't know a sensor the firmware sends -- update the suite, or untick that sensor. An unknown sensor stops the decoder reading the rest of its frame.
Sensors in the wrong order, or duplicated Delete all sensors and discover again, with the helicopter powered up after discovery starts.

See Telemetry Sensors for the full sensor list.