Configuring FC Flight Controller with ExpressLRS

I. Serial Port RX Settings

After connecting the receiver to the flight controller, you need to configure UART for serial RX. This is typically done on the Ports tab of the Flight Controller Configurator.
In the example below, the receiver is connected to UART1 (TX1 and RX1 pads), so the Serial RX column should be enabled on UART1 in the Ports tab.

Important

This is just an example. Set the ports according to how your peripherals (including the receiver) are wired.

Betaflight Serial RX Configuration Example

INAV Serial RX Configuration Example:

II. Serial Receiver Protocol

The ExpressLRS receiver based on UART uses the CRSF serial protocol to communicate with the flight controller.
Follow these steps to set up your serial receiver protocol:

1. In the flight controller configurator, navigate to the Receiver tab.
2. Set Receiver Mode or Receiver Type to Serial.
3. Set Serial Receiver Provider to CRSF.
4. Set Telemetry to Enabled. In INAV, this option can be found under the Telemetry Configuration Tab.
5. If you are using an analog FPV system or any FPV system that supports MSP DisplayPort or "Canvas Mode", ensure that the RSSI Channel is set to Disabled.
6. Ensure that RSSI ADC is also set to Disabled.
   Betaflight Serial RX Configuration Example:
   
   INAV Serial RX Configuration Example:
   

III. Software Inversion and Duplex Mode

The CRSF protocol requires a complete UART pair, uninverted and in full-duplex mode. To check these settings, use the CLI tab of the flight controller configurator and execute the following commands:

• serialrx_inverted should be set to OFF; can be set with the command: .set serialrx_inverted = off
• serialrx_halfduplex should be set to OFF; can be set with the command: .set serialrx_halfduplex = off
  After completing these settings, don't forget to use the save command to save the changes.

IV. RC Link Preset (Betaflight Only)

For Betaflight-based flight controllers, there are "RC Link Presets" available that configure feedforward smoothing and related link settings based on your packet rate and use case.

Important

Using no link preset or an incorrect preset for your packet rate may introduce unwanted noise and jitter in the feedforward, affecting setpoint tracking and thus flight characteristics.

To install the correct "RC Link Preset", follow these steps in the Betaflight Configurator:

1. Select the Preset tab
2. In the Presets tab, select Save Backup and save the backup to a safe location before applying any presets.
3. Search for "ExpressLRS" and select the link preset that matches your packet rate. If there is no direct match available, select the closest preset that is lower than your packet rate.
   
4. Go through the options by selecting the dropdown. Note: These are all optional, and if none apply to your situation, you can leave all unchecked.
5. Select "Pick" to stage the preset:
   
6. Select Save and Reboot to apply the preset:
   

Important

After configuring the Flight Controller Configurator for ExpressLRS, please close it. Keeping it open may prevent subsequent steps from completing correctly, especially when flashing through Passthrough. You must also unplug the FC flight controller from USB before proceeding with the next steps to flash the connection.

After configuring the flight controller, you can now proceed to the next step: Check the receiver firmware version
—— This article is referenced from ExpressLRS Getting Started: https://www.expresslrs.org/quick-start/receivers/configuring-fc/#rc-link-preset-betaflight-only