Your DBR4 Ships on 3.3.2. MAVLink Starts at 3.5.0
Quick Answer
Native ELRS MAVLink carries radio control and two-way ground-station data over one ExpressLRS link. For a RadioMaster Nomad and DBR4, update both ends to ExpressLRS 3.5.0 or newer first: our DBR4 listing specifies 3.3.2 pre-installed, which is too old. Then select MAVLink mode, wire one full UART and connect Mission Planner at 460800 baud.
Why the Firmware Version Matters
The trap is printed in our own catalogue. The RadioMaster DBR4 Xrossband Gemini receiver is listed with ExpressLRS 3.3.2, while native MAVLink needs transmitter and receiver firmware 3.5.0 or newer. If the MAVLink option is missing, do not rewire the aircraft: check and update the receiver, transmitter module and, when using Wi-Fi forwarding, the TX Backpack first.
This is not ordinary CRSF sensor telemetry. Native MAVLink lets Mission Planner or QGroundControl read parameters, upload missions and send commands while the same link still carries stick channels. It also makes the older ELRS AirPort method the wrong starting point for a new build: AirPort is a transparent serial bridge and gives up the shared RC-plus-data behaviour.
The Hardware Pair We Would Use
ExpressLRS requires ESP-based hardware for MAVLink; STM32-based modules cannot run this mode. The RadioMaster Nomad uses an ESP32 main controller, an ESP32-C3 backpack and two LR1121 radios. The DBR4 also uses an ESP32 and two LR1121 radios. That makes this pair a cleaner choice than legacy single-band 900MHz hardware, which the ExpressLRS project warns will transfer data slowly.
For a UK aircraft, flash the correct regional domain rather than leaving FCC915 firmware in place. We would begin on 2.4GHz while proving the wiring and parameter path, then choose a flight packet rate for the required range. The official guidance favours F1000 or 333Hz Full for fast 2.4GHz parameter and mission transfers, then 333Hz Full or a slower rate for flight. Browse our radio controllers and receivers only after checking that both ends are ESP-based.
ArduPilot and Mission Planner Setup
Wire DBR4 TX to flight-controller RX, DBR4 RX to flight-controller TX, plus regulated power and ground. Use a full, preferably DMA-capable UART; one-way receiver wiring cannot return MAVLink data. In the ELRS Lua script, set the receiver serial protocol to MAVLink on version 3, disconnect the receiver, then change Link Mode from Normal to MAVLink. Version 4 configures the receiver protocol automatically.
On ArduPilot, set the selected port to SERIALx_PROTOCOL=2, SERIALx_BAUD=460 and RSSI_TYPE=5, then reboot. Connect the external module to Mission Planner by USB and choose 460800 baud. MAVLink mode forces a 1:2 telemetry ratio and does not support Wide switch mode, so a greyed-out telemetry control is expected rather than a fault.
Our Gemini X guide explains the radio modes; our ArduPilot setup guide covers the wider flight-controller configuration. Our position is simple: prove parameter download and RC failsafe on the bench before removing a separate telemetry radio from an existing aircraft.
FAQ
Q: Why is MAVLink missing from the ELRS Lua script?
A: One end is commonly below ExpressLRS 3.5.0, or the hardware is STM32-based rather than ESP-based. Update both ends and confirm the hardware platform.
Q: Can ELRS MAVLink replace a SiK telemetry radio?
A: It can provide RC control and bidirectional MAVLink on one link, including parameters and missions. Validate throughput, failsafe and regional RF settings for the actual aircraft before removing a proven link.
Q: Can an internal ELRS radio connect to Mission Planner by USB?
A: Not directly. The ExpressLRS documentation says internal modules need the TX Backpack Wi-Fi path; an external module can use a direct USB serial connection.