The pilots that got into FPV as early as three or four years ago must have experienced the pain of accessing all kinds of information to get the receiver binding. In the fpv drone industry in 2021 the greatest innovation than the birth of the open source ExpressLRS radio control link RC system.
In this post you will learn about the ExpressLRS radio control link system in a few sections. If you are not familiar with the radio and receiver, you can check out the guide on radio and receiver guide.
What is ExpressLRS radio control link system (module)?
ExpressLRS(A.K.A ELRS) is an open source project based on IoT LoRa protocol for remote control models. Here is the official ELRS project from github .
Simply put it is a new protocol for radio control transmitting and receiving with open source software and hardware. It focuses on range and latency.
What is long range rc transmitter module?
Long range rc transmitter module mainly for OpenTX system to develop, support the mainstream OpenTX as the system of remote control. For example, Jumper series, FrSky series, TBS Crossfire, etc.
The three important parameters of the long range transmitter module
- Signal transmission frequency
The popular FPV RF signal transmission frequency has 915MHz and 2.4GHz. The signal transmission frequency is related to the hardware and cannot be switched between 915MHz and 2.4GHz. The main popular long-range transmitter module will use 915MHz.
- Command refresh rate
It is a parameter defined by the master controller. The faster the refresh rate, the lower the delay of the control, but the less stable the transmission. The upper limit of command refresh rate is limited by the transmission frequency of the signal.
- RF Power
The higher the RF power, the stronger the signal transmission capability. However, the final strength of the signal is related to the environment and factors such as the transceiver antenna.
What is the difference between ELRS module and FPV transmitter module?
ELRS can raise the limit refresh rate to 500Hz at 2.GHz signal frequency, which can ensure the stability of the transmitted signal while reducing the delay. The reason for this stability advantage is based on the IoT LoRa protocol, LoRa protocol uses chirp spread spectrum technology, which simply means that the characteristics of the signal spread spectrum can effectively reduce the interference of the same frequency band signal. The chirp spread spectrum technology is able to tune the signal code into a linear frequency conversion signal.
In the official data mentioned in the ELRS project ExpressLRS 900MHz 200Hz, the minimum transmission delay is only 5 milliseconds. The tbs crossfire has a transmission delay of 10 milliseconds at 150hz. So what can the difference of 5 ms bring? For top pilots, the 5ms difference in response time has its significance. For most pilots, this 5ms delay is not the concern, whether the connection is stable, whether the price is reasonable, whether the settings are reasonable, whether the compatibility is good is the reason to decide whether this transmitter module can be popular.
How to choose the frequency of ELRS module?
2.4GHz ELRS module is using a new generation of 2.4g chip: sx1280 open source production, can achieve ultra-low 500Hz high refresh rate, low latency performance of the basic earth’s strongest. sx1280 that tbs tracer, fatshark ghost, flysky 302 the same RF chip.
915MHz ELRS module can be self-made, can also be modified with R9M receiver. The highest refresh rate of 200Hz, higher than the TBS 150Hz. Receivers can buy more completed hardware.
If you are just flying for normal flights, 2.4G is the best choice. If you have the need for long-range flight, choose 915M because of its strong winding ability. But for this kind of long-range flight aerial photography, it is also recommended to use more than 1W with dynamic frequency conversion of the TBS 915 transmitter module.
How Do I Choose The Antenna For ELRS Module?
ELRS module will have an antenna: omnidirectional antenna or Moxon antenna.
First of all, we have to know the omni-directional antenna, that is, in the horizontal direction of the performance of 360 ° are uniform radiation, which is usually said to be non-directional. Moxon antenna belongs to directional antenna, is in a particular direction or a particular direction to transmit and receive electromagnetic wave is particularly strong, and in other directions to transmit and receive electromagnetic wave is zero or a very small antenna.
The antenna length is determined by the RF wavelength, only when the two are integer multiples of the wavelength relationship to maximize the effectiveness of electromagnetic oscillation. 2.4GHz frequency is higher, the wavelength is shorter, and the size of the antenna is smaller.
pro tips: when the ELRS module is not connected to the antenna, the current will be all concentrated in the IC internal, the power will be too large to cause serious heat, and even burn the antenna. So please install the antenna in advance before power on.
If a flight of several hundred meters is performed, using an omnidirectional antenna is enough.Moxon antennas are better directional and suitable for directional long-range flights.
The Difference Between ELRS Module And TBS Transmitter Module?
|ELRS Module||TBS Transmitter Module|
|Telemetry Capability||Excellent||TBS Receivers 500mW telemetry|
|Price||Can afford||More expensive than ELRS|
ExpressLRS Used Guide
Updating ExpressLRS Firmware
ExpressLRS has now been updated to version 3.1.2. Updating to the latest version will protect you from a number of potential problems. It is also recommended to update your newly purchased ExpressLRS hardware (if it is not the latest version)
How To Flashing/updating Your ExpressLRS
There are multiple ways to flash the ExpressLRS firmware into the TX or RX module. These depend on the hardware you are using and its capabilities (availability of a USB plug, availability of a WiFi ESP32 chip, etc.).
The methods available for the TX module are TX Update, WiFi Update, and UART Update.
For the RX module, the available methods are Betaflight passthrough, WiFi update and UART update.
Pro tips: If your TX and RX have ESP on board chips, then you can update available via wifi. If your TX module has a USB interface, then you can use the UART update method. Any RX can be updated via the Betaflight Passthrough or UART update method.
You can find the possible firmware flash methods for each hardware item here.
Download and install the ExpressLRS Configurator. You can download the ExpressLRS Configurator from here.
Step 1: Launch the ExpressLRS Configurator and select the firmware version.
Step 2: Setup in ExpressLRS Configurator.
Select the hardware for which you want to build the firmware and the type of update.
Then select the flash method, this step will determine which way the firmware will be flashed next.
Tx has two flashing method：
RX has three flashing method：
Receivers module (RX) firmware
In the Target settings option, after selecting “Device”, you must set the “Device Options” for the selected hardware. Here I choose to use BetaFPV Nano 900MHz as an example.
Regulatory Domains – Depending on your country region, choose between 915 or 868 frequency firmware settings.
Binding Phrase – Just like your VTX channel number, you should let the people you are flying with know so they don’t use the same phrase and cause problems. It should be a unique phrase that you can remember, not a password or secret.
AUTO_WIFI_ON_INTERVAL – Enables automatic start of WiFi updates at boot time. The timeout value can be customized (default is 60 seconds).
Once everything is set up, click the BUILD button (not Build and Flash button). This may take a few minutes.
After the configurator finishes building, a window should pop up with the firmware file named ” firmware.bin”, copy it to a place where you can easily find it later.
Transmitters module (TX) firmware
Flashing via USB/UART
If you select UART flash, then you can press the [ BUILD & FLASH ] button to create and flash bootloader the ExpressLRS module. Before this step, the transmitter module should be connected to the PC via USB cable.
The ExpressLRS Configurator will first compile and then will automatically detect the serial port to which the ExpressLRS TX module is connected and attempt to flush the compiled firmware into it.
If the ExpressLRS Configurator fails to detect the TX module, then you will see this error.
In this case, click on “Back” to manually select the serial port.
For additional flash methods, see the detailed ExpressLRS Official Guide.
The ExpressLRS receiver can be bound in two methods – automatically when using the same binding phrase, or conventionally by placing both TX and RX in binding mode.
The ExpressLRS receiver will automatically bind to the transmitter module if the firmware for both the TX and RX modules have the same binding phrase. You can set your custom binding phrase in the ExpressLRS Configurator.
Alternatively, you can bind any ExpressLRS receiver to any ExpressLRS transmitter by setting both to Bind Mode. In order to set the receiver to bind mode, you must cycle the receiver on and off 3 times, then the receiver will enter bind mode. The transmitter module can be set to bind mode by selecting the [Bind] option in the ERLS Lua script.
Some ExpressLRS transmitter modules have a bind button on the module that you can press to enter bind mode.
Here is how to bind the BetaFPV TX module. The LED will not blink when entering the bind state. 5 seconds later the module will automatically exit the bind state. Short press 3 times in a row to bind.
Installing/Soldering ExpressLRS Receivers
The ExpressLRS receiver uses the CRSF protocol to communicate with the flight control. Therefore, the ExpressLRS receiver should be connected in the same manner as the TBS Crossfire receiver. Any Crossfire receiver connection diagram is also applicable to the ExpressLRS receiver. In addition, the ExpressLRS receivers have the same pinout as the TBS Crossfire Nano receivers, so they can be mounted (soldered) directly to the FC board or adapter board just like the TBS Crossfire Nano RX.
The general rule is to connect the ExpressLRS receiver TX solder joints to the flight control RX solder joints and the RX solder joints to the TX solder joints. There is also GND to GND and usually the ExpressLRS receiver is powered by 5V.
ExpressLRS Module Tips
- The version of the transmitter module and the receiver version must be the same before you can bind.
- Is it convenient forfpv beginner to flash the firmware? It is not recommended for beginner to flash the ExpressLRS because ELRS requires some basic skills and time and effort. You can directly buy ELRS module kit.
- Flash rate can only be changed by the remote control before connecting with the receiver, if you change the refresh rate on the HF head after connecting, the signal will be lost.
- Hardware supported by ExpressLRS.
I really like ExpressLRS, because it is a system that open source programmers provide free access to the FPV community and I appreciate all the efforts that open source programmers make. ExpressLRS offers affordable remote alternatives to the popular TBS Crossfire and Frsky R9M.
The difference between ExpressLRS Module and fpv transmitter module has been mentioned in this article. If you don’t wanting to switch external modules going from crossfire to ELRS between models. Then just keep it as it is.