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What are Betaflight and CRSF? FPV flight controller basics

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Betaflight and CRSF come up in almost every conversation about FPV drones. Betaflight is the open-source firmware that runs on many FPV flight controllers; CRSF is a serial protocol that carries control commands and telemetry between the radio receiver and the flight controller. Understanding both makes it easier to see how add-on modules connect to an FPV drone.

What is Betaflight?

Betaflight is open-source firmware for the flight controller, the small board that reads the gyroscope and accelerometer, interprets pilot commands and drives the motors through electronic speed controllers. It is known for responsive, low-latency flight that suits FPV piloting.

Pilots configure it through a desktop configurator: receiver protocol, flight modes, rates, filters and on-screen display (OSD) elements are all set there. Several other firmwares in the FPV world share its roots or its concepts.

What is CRSF?

CRSF (often called Crossfire protocol) is a serial communication protocol between a radio receiver and the flight controller. It was introduced with a long-range RC link system and has since been adopted widely; the open-source ExpressLRS project, for example, also speaks CRSF to the flight controller.

Compared with older receiver protocols, CRSF is bidirectional: it carries channel data from the pilot to the drone and telemetry, such as battery voltage and link quality, back to the radio. It runs over a standard UART, so it needs only a few wires.

How they fit together

A typical FPV signal chain looks like this:

  • The pilot's radio transmitter sends stick commands over the air.
  • The receiver on the drone decodes them and passes them to the flight controller over CRSF.
  • Betaflight on the flight controller combines those commands with gyro data to stabilize the drone and drive the motors.
  • Telemetry flows back over CRSF to the radio, and flight information is shown to the pilot through the OSD on the video feed.

Why this matters for add-on modules

Because CRSF is a well-documented standard on a simple serial connection, external modules can sit alongside the receiver and flight controller without needing a custom airframe or proprietary electronics. This is the same principle behind brand-independent integration: a module that speaks the protocols the drone already uses can be fitted to many different builds.

IRA-1, for example, connects to Betaflight or MilBeta based flight controllers over CRSF with six cables, regardless of frame size.

IRA-1: integration and compatibility →

Frequently asked questions

Yes. Betaflight is open-source firmware, and its configurator is also free to download. Hardware compatibility depends on the flight controller board.

Both carry channel data from the receiver to the flight controller. SBUS is one-way, while CRSF is bidirectional and also carries telemetry back to the radio. CRSF is generally favoured on modern FPV setups for that reason.

Yes. ExpressLRS uses its own over-the-air link but talks to the flight controller using the CRSF protocol, so Betaflight treats it as a CRSF receiver.

The on-screen display (OSD) overlays flight information such as battery voltage, flight mode and warnings on the pilot's video feed, so the pilot can see it in the goggles without looking away.