1. Three protocol layers in an FPV drone
Air / radio
Transmits commands from the transmitter to the receiver: ELRS, Crossfire, Tracer, FrSky ACCST and FlySky AFHDS.
Receiver / serial
Moves channel data from RX to FC over UART or a dedicated input: CRSF, SBUS, iBUS and SRXL.
ESC / motor
Moves throttle commands from FC to ESC: DShot, PWM, OneShot125 and Multishot. This is separate from CRSF.
2. Radio protocols
ExpressLRS
An open modern standard for 2.4GHz and 868/915MHz. It offers low latency, long range, packet-rate choices and telemetry for freestyle, racing and long range.
TBS Crossfire / Tracer
Crossfire uses 868/915MHz and Tracer uses 2.4GHz. Both belong to the reliable Team BlackSheep ecosystem and provide two-way communication.
FrSky ACCST
D8 and D16 are older protocols. They can still work in simple conditions, but have fewer modern features than ELRS.
FlySky AFHDS 2A
A budget ecosystem for beginners. Use the matching receiver and iBUS, and check the range and telemetry of the exact model.
3. Receiver protocols: RX to FC
CRSF
A fast bidirectional digital protocol for ELRS, Crossfire and Tracer. Wire receiver TX to FC RX, receiver RX to FC TX, plus 5V and GND. It supports telemetry.
SBUS
An older one-way Futaba/FrSky protocol. It often uses an inverted signal and needs a suitable FC input or inverter.
iBUS / SRXL
iBUS is used by FlySky and SRXL by compatible Spektrum ecosystems. Select the protocol for the actual receiver, not only the transmitter brand.
| Equipment | Air link | Betaflight receiver | Connection |
|---|---|---|---|
| ExpressLRS | ELRS 2.4G / 900M | CRSF | Free UART: TX + RX |
| TBS Crossfire | Crossfire 868/915MHz | CRSF | Free UART: TX + RX |
| TBS Tracer | Tracer 2.4GHz | CRSF | Free UART: TX + RX |
| FrSky | ACCST D8/D16 | SBUS | UART RX / inversion |
| FlySky | AFHDS 2A | iBUS | UART RX |
4. Motor protocols: FC to ESC
DShot300 and DShot600 are digital protocols with CRC and no throttle-range calibration. Bidirectional DShot sends RPM data back from the ESC to FC and enables RPM filtering, which can reduce vibration and heat when the mechanics are sound.
5. VTX and configuration protocols
MSP is used for configuration, OSD and digital-display communication. SmartAudio and IRC Tramp control an analog VTX: channel, band, power and pit mode. If video works but VTX control does not, check the UART TX pad and the selected protocol.
6. Betaflight setup checklist
- In Ports, enable Serial RX on the UART where the receiver is soldered.
- In Receiver, select Serial receiver. Choose CRSF for ELRS/Crossfire, SBUS for FrSky and iBUS for FlySky.
- In Motors, choose DShot300 or DShot600 and verify motor order and direction with props removed.
- Enable Bidirectional DShot and RPM filtering only when the ESC and firmware support it.
- For VTX, verify SmartAudio, IRC Tramp or MSP DisplayPort and the correct UART TX.