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Getting telemetry on an Eachine QX 95

I recently got one of these cheapish indoor brushed quads. They are reasonable quality, and they have an 'SPRACINGF3EVO' clone brushed flight controller board, so they can run Betaflight without any hackery. Eachine has some more models like the QX 80 and the QX 90 that all seem to be differing only by the frame, but use the same electronics.

Unfortunately there isn't much documentation available for the FrSky micro Rx that they come with (if you order them with FrSky). It was a safe assumption that this would be a clone of the 'midelic' design of ATmega 328 / CC2500 based Rx. It works, but the way the craft comes preconfigured there is no telemetry.

I set out to try and change this, and after some trial and error I've come up with something that works:

  • get the latest firmware for 'FrSkyRx F802' from RCGroups;
  • hook up your board to your ISP programmer (see diagram for wiring);
  • use avrdude to flash the latest firmware avrdude -b 19200 -c avrisp -p m328p -P /dev/ttyUSB0 -v -F -U flash:w:FrskyRx_F802_PFS_SBUS_HUB_071016.hex;
  • connect the 'RXD' pad on the Rx to the TX on your flight controller;
    (caveat: if you are using UART1 on the SPRACINGF3EVO clone that the QX 95 comes with, the 'RX1' and 'TX1' pins on the diagram are swapped, and you have to connect the telemetry line to what is labelled as 'RX1)
  • set up Betaflight (or whatever else you use on your flight controller) to output 'FrSky' telemetry on this port.
  • have fun flying ;-)