Spotted this on the /r/multicopter subreddit. It's an open source firmware which can be flashed to existing R9 hardware and gives you a low-latency, minimal telemetry RC link. It can run at 200 Hz, 100 Hz or 50 Hz depending on whether you want speed or range, and the RX firmware supports CrsfShot on the TX side, and CRSF at the RX. It also might solve some of the issue people were having with R9 messing with feed-forward due to the variable packet rate.

It is a one-way trip, though. You can't flash the FrSky firmware back if you're done playing. Some more details:

Quote:ExpressLRS is an open source RC link for RC aircraft. It is based on SX127x hardware combined with an ESP8285, ESP32 or STM32 for RX and TX respectively.

ExpressLRS can be flashed into existing Frsky R9M hardware (RX and TX) or custom PCBs can be make to suit. It can run at 200 Hz, 100 Hz or 50 Hz depending on if you prefer range or low latency. This system does FHSS over a configurable number of channels. At 200 Hz it is the fastest 900/433 MHz RC link on the market with a Stick -> OpenTX > RF -> RX -> Serial Packet Latency of ~10ms or ~6.5ms on firmwares with crsfshot support.

Due to the optimized packet structure only basic telemetry that gives uplink/downlink information is currently supported.

TX and RX modules communicate via the standard CRSF serial protocol for easy use with Betaflight and openTX.

Compared to commerical systems ExpressLRS is also very affordable, a TX module can be built for $30 and recievers for $15-20.

RC Groups thread
Github page
Reddit thread

I know a few people here bought the R9 stuff when it was cheap and then got Crossfire anyway, so if you have unused R9 hardware lying around and a bunch of spare time then this might be worth a go.

I just read a little bit about it. very interesting project, a lot of potential I wonder how long before the Chinese manufacture gets a hold of this and start mass producting.

Myself and @Scopio have been following along and working with the ExpressLRS devs for some time now. We have some of their test PCB's too and are ready to trial them. A few of them are actually pretty local to us (3hrs drive away). It's definitely an awesome project, I was going to see if I could mod it into a Flysky i6 as an ultimate beginner LR setup, although those that know me here know I already have 300 too many projects... lols

I have a question about the mods that must be done to get 400k baud on r9m / taranis qx7. I just did the pull-up resistor mod to my r9m ACCST module, and my module binds to my r9mm receiver with express LRS in crsf mode...... But when I go to 400k baud rate, no telemetry data......I was under the impression the r9m needed the mod shown in the Express lrs wiki. But when you read further, they suggest that a mod is needed for the taranis transmitter as well.... Does anyone here have experience performing mods to either r9m and/or the Taranis series of radios?
When you click the hardware mod link in the wiki, it redirects to a site that shows a mod to the circuitry within the Taranis. Do I have to also mod my taranis? I was under the impression that if I modded my r9m, the Taranis mod was unnecessary....... Help. Thanks.

(12-Jan-2021, 11:11 PM)danielcmcguire Wrote: I have a question about the mods that must be done to get 400k baud on r9m / taranis qx7. I just did the pull-up resistor mod to my r9m ACCST module, and my module binds to my r9mm receiver with express LRS in crsf mode...... But when I go to 400k baud rate, no telemetry data......I was under the impression the r9m  needed the mod shown in the Express lrs wiki. But when you read further, they suggest that a mod is needed for the taranis transmitter as well.... Does anyone here have experience performing mods to either r9m and/or the Taranis series of radios?
When you click the hardware mod link in the wiki, it redirects to a site that shows a mod to the circuitry within the Taranis. Do I have to also mod my taranis? I was under the impression that if I modded my r9m, the Taranis mod was unnecessary....... Help. Thanks.

Don't hold me to it, but I believe you have to do the "crossfire" mod to a QX7.

https://www.team-blacksheep.com/products/prod:qx7mod

fantastic project!
me too, yesterday I stumbled upon the project while looking for information to setting betaflight to better filter my R9 system.
I was one step away from programming all the R9s I have, from enthusiasm,  (usually I flash any beta firmware I come across ).
I only stopped because I wanted to try the recommended RCsmoothing settings (FF_interpolate = 4 and RC_Smoothing with values of 30-40).

About of RCsmoothing, I was wondering if the settings for ExLRS would be the recommended ones for crossfire?
i.e. FF_interpolate = 3 and RC_Smoothing with values 8-20, or is it better?

I have read this information https://oscarliang.com/improve-radio-control-latency/

finally I was able to try ExpresLRS!
I reprogrammed a R900mini jumper, and used a TTGO v1 for the TX.
I also tested on a Jumper T8SGV2+, even if on DeviationTX cannot change settings via the menu

Now I try to put him on a quad and if weather permits, I do a flight test!

Happymodel are about to release an ExpressLRS module and receiver using dedicated hardware for that protocol which is already flashed with ExpressLRS firmware (see the images below). BetaFPV have apparently also jumped on the bandwagon and will be doing the same. The Happymodel one (below) is 900MHz and the BetaFPV one will be 2.4GHz.

This is great news!
I was going to order the discrete components and custom pcb to build one ...
Now I would like to know more!
Tell us everything you know! hahahahah 
what else has leaked?

ExpressLRS just got 33 kilometers without failsafe using 100mW and 250hrtz refresh rate packet.
He was going to go further but ran out of battery.
He is going for 100 kilometers soon just needs a bigger wing.

It doesn’t surprise me it being manufactured and marketed.I’ll likely get a starter kit and hopefully it’ll come with 3-6 receivers.

One thing to keep in mind is that ExpressLRS doesn't currently provide any telemetry data back to your transmitter even at close range, so you are purely reliant on telemetry data in your OSD. That said, Crossfire doesn't provides telemetry data at those sort of extreme distances either, but it does at shorter distances.

(15-Feb-2021, 05:30 PM)SnowLeopardFPV Wrote: One thing to keep in mind is that ExpressLRS doesn't currently provide any telemetry data back to your transmitter even at close range, so you are purely reliant on telemetry data in your OSD. That said, Crossfire doesn't provides telemetry data at those sort of extreme distances either, but it does at shorter distances.

they are working to implement all the telemetry, to date I see about 14 values ​​on the radio. later I'll take a screenshot.

(15-Feb-2021, 05:40 PM)Corrado-c Wrote: they are working to implement all the telemetry, to date I see about 14 values on the radio.  later I'll take a screenshot.

Sorry, I guess I should have added more clarity around my statement. The ExpressLRS devs state that anything more than the most basic telemetry isn't supported as per their statement below:-

"only basic telemetry is currently provided (VBAT, downlink/uplink LQ and downlink/uplink RSSI), work is underway for full telemetry support"

What are the 14 sensors you are seeing? And do they all have flashing asterisks next to them?

here I am finally at home,
don't worry, I wasn't clear either! I almost never am ahhahaha. first I answered you quickly while I was traveling.
You are rightly right because their home page still states that.
Obviously a lot of data is from the RX itself, but they also start communicating FC data.




hey Snow, you need to tell us more about happymodel dedicated hardware

OK, I guess the development has moved on quite a bit since they last updated the information on their home page. Do you still get all telemetry data at the highest RC link refresh rate?