ExpressLRS is an open source long range RC system that focuses on range and latency. It’s also way more cost effective compared to TBS Crossfire and Frsky R9M. If you are looking for a cheaper way to start long range flying and prefer open source, check out ExpressLRS.
ExpressLRS offers an affordable long range alternative to the popular TBS Crossfire and Frsky R9M. They even claim to outperform these commercial systems in terms of latency as well as range!
ExpressLRS is based on SX127x hardware combined with an ESP8285, ESP32 or STM32 MCU for RX and TX respectively. It’s using LoRa modulation, same as ImmersionRC Ghost and Crossfire, that’s why it has noticeably better range than systems that aren’t using LoRa such as TBS Tracer.
The 900MHz version of ExpressLRS runs at a maximum 200Hz update rate, which is higher than Crossfire’s 150Hz. The 2.4GHz version can even run at 500Hz! (up to 1000Hz on custom hardware).
TX and RX modules communicate via the standard CRSF serial protocol (Crossfire) for easy use with Betaflight and OpenTX.
Right now, ExpressLRS is not as user-friendly as Crossfire, but hopefully it will only get better with time. I will surely publish more content around ExpressLRS in the future.
ExpressLRS Github Page: https://github.com/AlessandroAU/ExpressLRS
Getting The Hardware
At the beginning, you had to build your own receiver and transmitter module (yea, not easy), but now you can just buy them off the shelf.
You can build your own receiver and transmitter module from scratch by getting the right components, ordering your PCB and solder those tiny little chips on the board. This is probably the cheapest way, a TX module and receiver costs only $30 and $15-20 respectively to build. See their Github page for more info.
You can also flash the ExpressLRS firmware to existing Frsky R9M hardware.
However, the process is irreversible, meaning you can’t flash Frsky firmware back on the hardware. Update: you can now flash Frsky firmware back on R9 hardware if you wish.
The most convenient way is to just buy the receivers and transmitter module that are made for ELRS. They are inexpensive, designed specifically for the ExpressLRS and already loaded with the firmware, so they are basically plug and play.
The transmitter module is compatible with almost all modern radios with JR module bay, such as the Radiomaster TX16S, Jumper T12, T16 and T18, Frsky Taranis etc. Hopefully “Lite” module will be available soon too for smaller radios like the Jumper T-Lite and Frsky X9-Lite.
There are two frequencies available, 900MHz (915/868) and 2.4GHz. Apart from range, the main difference is that the 900MHz system can only do 200Hz update rate, while the 2.4GHz can do 500Hz, even up to 1000hz on custom radio hardware. Unless you are crazy about range, I think 2.4GHz might be more suitable for most people, it still can do some serious range (miles).
915MHz / 868MHz (HappyModel)
Here are the specs of the transmitter module and receiver:
ES915TX Transmitter Module
- Dimension: 55mm*39mm*13mm(include heat sink)
- Weight: 23gram (exclude antenna)
- Antenna connector: SMA
- VCC input: 5~13v, Recommend 5v~9v
- RF Frequency Range: 902MHz ~ 928MHz
- Maximum Output Power: <33dBm(For >27dBm operation, we recommend add a fan for force cooling)
- VCC input: 3.7~24v Recommend 5v~12v
- Operation current: ~100Ma
- Rx To FC protocol: CSRF
- RF Frequency Range: 902MHz ~ 928MHz
- Dimension: 16mm*10mm*3mm
- Weight: 0.70 gram (exclude antenna)
- Antenna connector: IPEX4
- Telemetry output Power: <17dBm
Apart from 900MHz, HappyModel is now also making a 2.4GHz system for ELRS. The advantage of 2.4GHz is the much smaller antenna and higher update rates (up to 1000Hz vs 200Hz). Although the range is not going to be as good as the lower frequency 900MHz, but 2.4GHz will still be able to give you a few kilometers of range in ideal condition, that’s more than enough for most people.
- TX Module: https://oscarliang.com/product-a3r9
- PP Receiver: https://oscarliang.com/product-1nfv
- EP1 Receiver: https://oscarliang.com/product-xuu7
- EP 2 Receiver: https://oscarliang.com/product-51w0
- Receivers at Makerfire: https://oscarliang.com/product-mnpg
Here’s the 2.4GHz ELRS TX module:
Happymodel is making these tiny receivers with built-in antenna (the black tower – that’s the whole antenna) – ELRS PP, EP1 and EP2.
The differences between PP, EP1 and EP2 are the processor (STM32 and ESP8285): PP has STM32, EP1 and EP2 has ESP8285. Performance wise they are similar, but the STM32 chip has a smaller form factor. The other possible difference is that ESP8285 has WiFi capability while the STM32 chip doesn’t.
Some of these nano receivers has built-in ceramic antenna (the black block), it’s so neat and small, no more antennas hanging out getting chopped by spinning props.
As it’s going to be buried inside the frame, it won’t perform as well as full size antennas when it comes to range. But for some people this is the perfect solution if they are looking for the absolute smallest or simplest build. For example Tiny Whoops would absolutely benefit from such ExpressLRS receivers as range is not a priority but size, weight and convenience.
How to Use?
In Model settings, go down to External RF, and select CRSF. That’s it. Of course there is a lot more info on Github if you want to master this system.
I will be publishing some tutorials in the coming weeks (around May/Jun 2021).
Telemetry is constantly being improved, currently supporting at least 14 types of data, including VBAT, current, downlink/uplink LQ and RSSI.
Telemetry screenshots from IntoFPV user Corrado-c.
ExpressLRS is available on both 2.4GHz and 900MHz so some of the tests here are done on different frequencies. Definitely a ton of potential with ExpressLRS by looking at promising test results like these :)
|Max Dist.||Freq||Pkt Rate||TX Power||Link to DVR|
- Feb 2021 – Article created
- Apr 2021 – 2.4GHz version by Happymodel announced, added info regarding its TX and RX options