Everything You Need To Know About ELRS

Overview

Every drone requires a radio link between the controller (often referred to as the transmitter or radio) and the receiver on the drone. For most pilots, ExpressLRS is the best protocol to use due to its reliability and low latency. One of the huge upsides to using ELRS is the constant development and new version releases, but it can also complicate the process. If the transmitter firmware version does not match the receiver firmware version, it may or may not work properly. It’s best practice to update the firmware on both the transmitter and receiver to the same version and it will also allow the two to bind automatically with a binding phrase. 

This guide will explain how to do all of this via the Wi-Fi interface. There are alternative methods, and this is assuming you have a radio with the ELRS script already loaded from the factory – most modern radios do. If you are missing the script, want alternative methods, want more information on features, or otherwise need more ELRS information, refer to the extensive ELRS documentation at expresslrs.org or ask in the official PyroDrone Discord: https://discord.gg/AYUJyvKH4d.

Safety Warning: Many drones require the battery to be plugged in to require the receiver. I suggest you set your video transmitter to pit mode to limit the heat produced, especially for high output analog VTXs. It’s also important to remove your props before doing any software configuration that requires a battery. It is extremely uncommon, but entirely possible, that the motors begin spinning. Stay safe, remove your props!

Installing ELRS Configurator

You’ll need the ELRS configurator to build the firmware you’ll need for both your receiver and transmitter. This can be downloaded from https://github.com/ExpressLRS/ExpressLRS-Configurator/releases and installed on Windows, Mac OS X, and Linux. The same computer that you use for Betaflight Configurator should work.

Updating ELRS Transmitter Firmware

In the ELRS configurator, select the newest release version, your transmitter brand, frequency, and device. I have a Jumper T15, so I’ve selected these options. We will also select the Wi-Fi flashing option, although there are other methods.

We will also select the regulation band based on location. I live in the US, so I will be selecting ISM. You should enable the binding phrase and create a code unique to you that other pilots are unlikely to use. This will also be used for all of your receivers and will allow them to automatically bind to your transmitter immediately. At the bottom, select build.

It may take a moment, but the program will build your firmware and open file explorer to it. This is the file we will be uploading to the transmitter next.

On your transmitter, enter the LUA script and select Wi-Fi connectivity and then enable Wi-Fi. This will activate a Wi-Fi access point (hotspot) than can be connected to using your computer or phone. It’s easiest to do this with a computer, although mine had issues because it’s also connected to ethernet. Instead, I moved the firmware file to my phone. The steps are the same regardless. The password to the access point is expresslrs and the SSID is ExpressLRS TX. This would be ExpressLRS RX for a receiver, and the password is the same.

You may be prompted to “log in” to the network. If not, go to the address 10.0.0.1 in your browser. Here, you can upload the firmware file under the update tab to flash the firmware to your transmitter. This will also display your device type and firmware version for both transmitters and receivers.

After updating your firmware, you can adjust a few options in the LUA script to your liking. If you aren’t sure on these options, you can leave them as default. Personally, I usually use 250Hz packet rate, dynamic power, and standard telemetry rates. It is important to turn off model match as it complicates the usage of multiple receivers. This option can be seen in the images from the above steps.

Updating ELRS Receiver Firmware

These steps are intended for serial receivers. If you have an all-in-one board with an SPI receiver, the steps are different.

In the ELRS configurator, you’ll follow the same steps used for the transmitter to select your device type, binding phrase, and other assorted settings. We will select Wi-Fi flashing option and build, same as last time. If you aren’t sure what device you have, it will show up when you log into the access point.

ELRS receivers, by default, create an access point after one minute of not being connected to a transmitter. This will require powering up your receiver, which means using a battery for most quads. If you plug in a battery while configuring your drone, remove your propellers. It’s unlikely but not unheard of for them to spin up during configuration. Your VTX may also heat up, and it’s suggested to use pit mode for situations like this.

Log into the access point and upload the firmware you built the same way we did for the transmitter. Make sure to use the new firmware you’ve built and not the same file that was uploaded to the transmitter. The bind phrase will automatically be used in both devices, and after a power cycle they will be bound and working. 

An easy way to check if a receiver is bound is to watch the LEDs. When you turn on and off your radio, the LEDs on the receiver will change accordingly. This doesn’t require you to know what each color or flash means, only that they are different. If they are bound but not working, make sure model match is turned off for both devices. This is accessible in the Wi-Fi page for the receiver under the options tab.

Betaflight Settings

If you have a BNF drone, this may have already been set up. If it works, go fly! You can check if it’s working in the receiver tab. 

If not, you will have to make sure a couple settings are correct so that the flight controller can communicate with the receiver. In the Betaflight receiver tab, you’ll notice a receiver protocol. While there is a drop-down menu, recent versions of Betaflight only include one protocol and it will not let you select a different protocol. The flight controller communication protocol for ELRS is CRSF and the flight controller will need to be flashed again to change this if it’s wrong. If you notice that your channels are in the wrong order (for example, your throttle stick corresponds to the pitch channel) you can change your channel map. For more customization, change the settings in your radio.

Additionally, the Betaflight ports tab must be set up. The UART that your receiver is connected to must have the serial receiver switch enabled.

It’s also suggested to use a Betaflight preset for the frequency of your ELRS link to improve RC smoothing, but it is not necessary. Select the preset, your options, and then save and reboot.

You may also need to set up modes in the modes tab. An arm mode is required and should always be on channel 5, which is only a two-position channel with ELRS. Acro is the default flight mode and doesn’t have a mode option at all. If you want a flight mode such as angle, you can add it here.

Happy Flying!

Written by JasonFPV