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How to use ExpressLRS (ELRS) / Long-distance, high-speed communication protocol

Here, I have summarized the basics of the procedure for controlling a drone using ExpressLRS(ELRS) : new communication protocol for radio-controlled aircrafts.
For more information on Tiny Whoops, see Introduction to FPV drone for beginner / How to fly Racing drone .

What is ExpressLRS(ELRS)

ExpressLRS transmitter in working
ExpressLRS (ELRS) is a new communication protocol for radio-controlled aircrafts that is being developed as open source. It is developed based on LoRa (SX127x / SX1280 chip), an open power-saving wireless communication technology developed by Semtech . The first firmware (Ver 0.1.0 RC1) was released in January 2021, and has been actively developed since then. The bands used are 915 MHz(FCC), 868 MHz(EU) and 2.4 GHz. It has a long radio wave range ( about 10km - 30km at 2.4GHz output 100mW ) and enables high-speed communication with low latency (adjustable in the range of 50Hz-250Hz (868/915 MHz) / 500Hz (2.4GHz)). Can be used with transmitters that support OpenTX/EdgeTX LUA scripts or TBS Crossfire (CRSF). Each manufacturer is releasing compatible products one after another. However, since it is a specification under development, improved versions of each product and firmware are appearing one after another, and some research is required to master it.
ExpressLRS official site holds competition for the range of radio waves . If you get good results, why don't you try to enter?

What is TX Backpack

It is one of the optional functions of Express LRS. You can wirelessly control FPV-related devices from the radio using a protocol called espnow. For example, you can change the reception frequency of FPV goggles with the radio. To use this feature, both the ExpressLRS transmitter and thecontrolling device must have ESP8285 chip. This ESP8285 chip is called "TX-Backpack".

ExpressLRS(ELRS) setting procedure

Here, we will explain step by step how to set the transmitter / receiver of ExpressLRS (ELRS).
To use ELRS transmitter, OpenTX on the radio must be upgraded to 2.3.12 or later. (Available in all versions of EdgeTX)
Install ExpressLRS Configurator
Install the tool "ExpressLRS Configurator" on your computer. This is a tool used to configure, build and update transmitter and receiver firmware.
Attach ExpressLRS transmitter to radio
If you use an external ELRS transmitter, install it in the module bay of your radio. Then store ELRS Lua script in "\SCRIPTS\TOOLS\" folder of SD card in the radio. And create "MODEL" of the drone you want to bind in radio (OpenTX/EdgeTX).
Update ExpressLRS transmitter firmware
ExpressLRS is a protocol under development, so it is being upgraded frequently. There are two ways to update, one is to use a USB cable (UART) and the other is to use Wifi.
Set up ExpressLRS transmitter
You can configure ExpressLRS transmitter by launching ELRS Lua script in radio. You can change packet rate and output power .e.t.c,. If the transmitter itself has a display and joystick, you can also use it instead of Lua script to configure it.
Update ExpressLRS receiver firmware
Update receiver firmware to match transmitter version. For external receivers connected via UART, use ExpressLRS Configurator to update. For receivers built in FC (Flight Controller) connected via SPI, receiver firmware is included in the firmware of FC. In this case, use Betaflight Configurator , to update the FC firmware by upgrading it.
Bind transmitter and receiver
There are two ways to bind, one is to use "watchword" called "Binding Phrase" and the other is to bind manually. And the setting method differs depending on whether you are using external receiver or FC (Flight Controller) built in receiver.
You can read detailed procedure by clicking "Quick Start" button and turning the page on ExpressLRS official site .

Selecting antenna mode: What is Gemini mode?

From ExpressLRS version 3.3, a new antenna mode "Gemini" has been implemented. This is a function that simultaneously transmits and receives one packet data using two different antennas and two frequencies. This allows for more stable data transmission and reception. On the other hand, the radio's battery consumption will also increase.
To use Gemini mode, you need a transmitter that supports Gemini mode and a receiver that supports Gemini or True Diversity mode. Both firmwares must be updated to ExpressLRS version 3.3 or later. Start the ExpressLRS Lua script on the radio and set the "Antenna Mode" field to "Gemini". Then select the name of the receiver you are binding from the "Other Device" menu and set the "Rx Mode" field to "Gemini".
The operation changes as follows depending on the antenna mode specification of the transmitter and receiver.
ExpressLRS Antenna Mode
Antenna Mode(transmitter) Rx Mode(receiver) Operation
ANT1/ANT2/Switch Single Single
Diversity Diversity
Gemini Single
Gemini Single Single
Diversity Diversity
Gemini Gemini
The meaning of antenna mode is as follows.
ExpressLRS Antenna Mode
Transmitter antenna mode Meaning
ANT1/ANT2 Only one of the two antennas specified will be used for communication.
Switch Communicate by switching between two antennas.
Gemini Specifies Gemini mode.