ExpressLRS (ELRS)
ExpressLRS (ELRS) is an open-source, long-range, low-latency radio control link for RC aircraft. In just a few years, it has become the most popular RC link protocol in FPV, overtaking proprietary systems like FrSky, Crossfire, and even DJI’s built-in radio.
Why ELRS Won
Section titled “Why ELRS Won”- Open source: No licensing fees, community-driven development
- Extremely low latency: As low as ~2ms at 1000Hz packet rate
- Extremely long range: 100km+ demonstrated at lower packet rates
- Dirt cheap: TX modules and receivers start under $15
- Built into radios: Most new Radiomaster and other transmitters ship with ELRS built in
- WiFi configuration: Update firmware and change settings over WiFi from your phone
- Community: Massive, active community constantly improving the protocol
How It Works
Section titled “How It Works”ELRS uses the 2.4GHz (most common) or 900MHz frequency band to send control data from your radio transmitter to a receiver on the drone.
The transmitter has an ELRS TX module (internal or external) that sends packets. The drone has an ELRS receiver that receives packets and sends channel data to the flight controller over CRSF protocol.
Packet Rate and Range
Section titled “Packet Rate and Range”ELRS lets you choose your packet rate, which trades latency for range:
| Packet Rate | Latency | Range | Best For |
|---|---|---|---|
| 1000Hz | ~2ms | Short-medium | Racing (lowest latency) |
| 500Hz | ~4ms | Medium | Freestyle (great balance) |
| 250Hz | ~8ms | Long | Long range, general flying |
| 150Hz | ~13ms | Very long | Long range cruising |
| 100Hz | ~20ms | Maximum | Extreme long range |
| 50Hz | ~40ms | Maximum+ | Extreme long range |
For most FPV flying, 500Hz is the sweet spot — imperceptible latency with excellent range. Racing pilots may prefer 1000Hz. Long-range pilots drop to 250Hz or lower.
2.4GHz vs 900MHz
Section titled “2.4GHz vs 900MHz”| Band | Pros | Cons |
|---|---|---|
| 2.4GHz | Tiny antennas, more channels available, most popular | Slightly less penetration through obstacles |
| 900MHz | Better range and penetration through trees/buildings | Larger antennas, fewer channels, less common |
2.4GHz is the default recommendation for most pilots.
Hardware
Section titled “Hardware”Transmitter (TX) Side
Section titled “Transmitter (TX) Side”- Internal TX module: Built into the radio. Radiomaster Pocket, Zorro, Boxer, TX16S all have ELRS internal module options.
- External TX module: Plugs into the JR bay on the back of your radio. BetaFPV Micro TX, Happymodel ES24TX, RadioMaster Ranger.
- Most new radios ship with ELRS. If yours doesn’t, an external module is $15-30.
Receiver (RX) Side
Section titled “Receiver (RX) Side”ELRS receivers are tiny and cheap:
| Receiver | Size | Antenna | Price |
|---|---|---|---|
| BetaFPV EP1/EP2 | Tiny | Ceramic | ~$8-12 |
| Happymodel EP1/EP2 | Tiny | Wire/ceramic | ~$8-12 |
| RadioMaster RP series | Small | Dipole/T-antenna | ~$10-15 |
| Matek R24-D | Standard | Dipole | ~$12-15 |
Diversity receivers (two antennas) provide better signal reliability. Recommended for long range. Most receivers have a single antenna, which is fine for normal flying.
Antenna Types
Section titled “Antenna Types”- Ceramic: Smallest, lowest performance. Fine for whoops and close range.
- Wire dipole: Good all-around. Standard for most builds.
- T-antenna: Best range in a small form factor. Recommended for 5” builds.
- Immortal-T: A popular DIY antenna design with excellent performance.
Binding
Section titled “Binding”Connecting your TX and RX for the first time:
Binding Phrase (recommended):
- In ELRS Configurator, set a binding phrase when flashing TX and RX firmware
- TX and RX with the same binding phrase will automatically connect on power-up
- No manual binding procedure needed
Manual Binding:
- Put the RX into bind mode (usually: power on while holding the bind button, or 3 quick power cycles)
- Put the TX into bind mode (through EdgeTX ELRS Lua script)
- They’ll connect and remember each other
Betaflight Configuration
Section titled “Betaflight Configuration”- Ports tab: Enable “Serial Rx” on the UART your ELRS receiver is connected to
- Configuration tab:
- Receiver Mode: Serial
- Serial Receiver Provider: CRSF
- Receiver tab: Verify channels respond correctly. ELRS uses AETR channel order by default.
ELRS Lua Script
Section titled “ELRS Lua Script”EdgeTX radios can run the ELRS Lua script to configure settings from the radio:
- Packet rate
- TX power
- Switch mode (hybrid 8-channel, wide 16-channel)
- Telemetry ratio
- Dynamic power (auto-adjusts TX power based on link quality)
Access via: System > Discover > ELRS (or bind the Lua script to a model)
Firmware Updates
Section titled “Firmware Updates”ELRS firmware is updated frequently. Update via:
- WiFi: ELRS receivers and TX modules can expose a WiFi hotspot. Connect from your phone/laptop and upload new firmware through the web UI. This is the easiest method.
- ELRS Configurator: Desktop app to build and flash firmware with custom options.
- Betaflight Passthrough: Flash the receiver through the FC’s USB connection.
Keep TX and RX on the same firmware version. Mismatched versions can cause connection issues.
Telemetry
Section titled “Telemetry”ELRS supports telemetry — data sent back from the drone to your radio:
- Battery voltage
- Current draw
- RSSI / Link Quality
- GPS coordinates
- Flight mode
Telemetry rate is configurable. Higher telemetry ratio = more frequent updates but slightly less headroom for control packets.
Set up telemetry sensors in EdgeTX: Model > Telemetry > Discover Sensors.
- Use a binding phrase: Much easier than manual binding, and you never have to rebind
- 500Hz is the default recommendation: Switch to 250Hz only if you need extra range
- Dynamic Power: Enable this — it reduces TX power when you’re close (saves battery, reduces interference) and increases when you fly out
- Link Quality (LQ) over RSSI: LQ in OSD is more useful than RSSI for monitoring ELRS link health. LQ of 100% means every packet arrived. Below 80%, start heading back.
- WiFi for updates: Way easier than USB flashing for receivers