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RC Setup

The 305ap supports several RC protocols. Which port and protocol you use depends on your receiver type.

Option A — RC IN Port (SBUS, CRSF/ELRS, and Others)​

Port: UART5 (ttyS4), labeled RC IN

UART5 is configured as a single-wire half-duplex port. The signal line is PB13. Connect your receiver's output to this pin.

This port works with:

  • SBUS (e.g. FrSky, Futaba)
  • CRSF / ELRS (receiver TX to the RC IN signal pin)
  • DSM/DSMX (via spektrum satellite adapter)
  • Single-wire PPM

No QGC configuration is needed. With RC_INPUT_PROTO = Auto (the default), the RC driver detects the protocol automatically. CRSF RC input on this port has been verified on the production test jig.

CRSF telemetry

CRSF telemetry back to the transmitter (link statistics, battery) needs a full-duplex UART. It has not been verified on the single-wire RC IN port. If you need it, use Option B.

Option B — CRSF / ELRS with Telemetry (Telem 1)​

Port: UART4 (ttyS3), labeled Telem 1

Connect your receiver's TX to the FC's RX (PA1) and the receiver's RX to the FC's TX (PA0).

Configuration in QGroundControl​

  1. Go to Vehicle Setup → Parameters
  2. Free the port: set MAV_0_CONFIG = Disabled (MAVLink uses Telem 1 by default)
  3. Set RC_CRSF_PRT_CFG = TELEM 1
  4. Optionally set RC_CRSF_TEL_EN = 1 to send telemetry to the transmitter
  5. Reboot the flight controller

The CRSF baud rate (420000) is set automatically by the driver.

ELRS

ExpressLRS receivers use CRSF protocol. The setup is identical to CRSF above.

Option C — CRSF / ELRS with Telemetry (Telem 2)​

Port: UART7 (ttyS6), labeled Telem 2

Same procedure as Option B but set RC_CRSF_PRT_CFG = TELEM 2 instead. Telem 2 has no function by default, so there is no MAVLink instance to disable.

Verifying RC Input​

In the MAVLink Console (QGC → Analyze Tools → MAVLink Console):

listener input_rc

This prints raw RC channel values. Confirm all channels respond correctly to stick movements.

Flight Mode Assignment​

After RC calibration in QGC, assign a switch to flight modes:

  1. Vehicle Setup → Flight Modes
  2. Assign the mode channel to your desired switch
  3. Configure at least: Stabilized, Position, Return