Connecting ELRS Receiver to Pixhawk 2.4.8 under PX4 Pro - Possible or Not? Need Guidance

PX4 Autopilot
1

Hello,
I wanted to ask some questions about the connections to be made with Pixhawk 2.4.8 (sorry, but I’m new).

I have Pixhawk 2.4.8 and ELRS receiver.
Recently I have successfully paired them following the guide on the ELRS site Elrs guide, but it works only for ardupilot.
So i’m just struggling to find analog of SERIALx_PROTOCOL = 23 (RCIN) and
RSSI_TYPE = 3 settings in PX4

Thanks!

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ELRS receiver communicate with FMU through CRSF protocol. PX4 does not support this protocol. So, in order to do this you need to include a CRSF to SBUS converter.

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Short answer, yes it’s possible.
How to do it?
You need to set RC_CRSF_PRT_CFG parameter to the serial that you’re using. BUT You can’t use prebuilt PX4 release (or main) firmware for this, as it depends on PX4 modules crsf_rc. To add RC_CRSF_PRT_CFG to parameter list you need to create your own PX4 build

  1. Get PX4 repo and needed items for build (Follow this guide - Building PX4 Software | PX4 User Guide), i recommend using ubuntu or WSL ubuntu
  2. Build firmware for pixhawk 2.4.8, to do it run “make px4_fmu-v3_default”
  3. Change config by command “make px4_fmu-v3_default boardconfig”.
    a)In the PX4 board config tool, navigate to the drivers submenu, then scroll down to highlight rc_input.
    b) Use the enter key to remove the * from rc_input checkbox.
    c) Scroll to highlight the RC submenu, then press enter to open it.
    d) Scroll to highlight crsf_rc and press enter to enable it.
    e) Save and exit the PX4 board config tool.
  4. Run build again “make px4_fmu-v3_default”
  5. Get your build in “\build” folder and install it to your pixhawk
  6. Set RC_CRSF_PRT_CFG to serail that you are using, in my case Serial 4/5 port

PS: I have connected my receiver to the Serial 4/5 port.
Useful links: Reptile Dragon 2 (RD2) Build | PX4 User Guide

3 Likes
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Hello there , I am having a bit of trouble understanding it , I am totally new to this ,
I have a Pixhawk 2.4.8 with me and Mission Planner 1.3.80 and firmware Copter V4.4.1 OFFICIAL. I am planning to buy TX12 Mark II Radio Controller (with ELRS, Mode 2 , FCC region), , I won’t be getting a receiver along with the transmitter . Please suggest me some receiver.
and secondly If I have receiver and transmitter is it enough for me to actually be able to control the quadcopter? or do I have to buy any more additional hardware to properly interface all of them together?.

(I am not sure if I was clear , for example earlier I had Fsi6 Flysky Fs-I6 2.4G 6Ch Afhds Rc Transmitter Controller with Receiver, all I had to do was bind RC and receiver , connect receiver to Pixhawk 2.4.8 calibrate RC and I was able to fly) Is it the same case with the TX12 Mark II Radio Controller (with ELRS, Mode 2 , FCC region) too once I buy the receiver ? or do I have to buy any other convertor/ similar hardware for it to work with Pixhawk 2.4.8 and mission planner.

apologies for this long post , English isn’t my strongest point.

5

I still very confuse with all the parameter, is there any easy way?

This is what i found using Copilot:

Certainly! You can indeed use an ELRS (ExpressLRS) receiver with a Pixhawk 2.4.8 flight controller. Here are some key points to consider:

  1. ELRS Protocol:
  • ELRS is an open-source implementation of the closed-source CRSF protocol from TBS (Team BlackSheep).
  • It refers to both the over-the-air protocol and the protocol used between the radio receiver (RX) and the flight controller.
  • ELRS is compatible with Pixhawk controllers.
  1. Serial Ports on Pixhawk 2.4.8:
  • The Pixhawk 2.4.8 has six serial ports (UARTs) available for connecting peripherals.
  • These ports are numbered from 1 to 6.
  • Any of these UARTs can be used for ELRS communication.
  1. UART Numbering:
  • The UART number often doesn’t directly match the serial port number on these ports.
  • The serial port is what you configure, and the UART number is sometimes used for labeling.
  • For ELRS, you do not need flow control, so any UART can be used.
  1. Choosing a UART:
  • Since ELRS doesn’t require flow control, you can use any UART.
  • The Pixhawk 2.4.8 has three general-purpose serial ports (Telem1, Telem2, and Telem3).
  • You can connect your Radiomaster RP1 ELRS receiver to either the Telem2 or Telem3 port.
  • Both are suitable choices, and you can configure them as needed.

Remember that ELRS is a great choice for long-range communication, and with the Pixhawk 2.4.8, you have flexibility in selecting the UART for your ELRS receiver. Happy flying!

Hope someone can help me out here.