ELRS/CRSF control lane

The ground station already receives video and telemetry from the drone over WFB-ng. The control lane adds an independent, low-bandwidth link the other way: the ground station drives an ExpressLRS (ELRS) transmitter module over USB serial and generates the RC link itself. WFB-ng stays the link for video and full-rate MAVLink.

A second link that moves the sticks is safety-critical. Validate your module, antennas and failsafe behaviour on the bench, read Safety, and confirm your setup meets the radio rules where you fly.

Modes

A module runs one mode at a time, set by radio.crsf.mode:

Mode	What the module carries
`crsf_rc` (default)	The 16 CRSF RC channels, sent to the drone’s ELRS receiver. The lane also decodes the telemetry the module returns (link statistics, GPS, battery, attitude, flight mode).
`mavlink`	The module becomes a MAVLink carrier that the agent’s MAVLink router ingests. It is telemetry only until `radio.crsf.mavlink_command_enabled: true`. The RC lane stands by.
`airport`	A raw serial data pipe.

Channel sources

In crsf_rc mode, radio.crsf.channel_source decides what feeds the channels:

Source	Feeds the channels from
`hid` (default)	The primary gamepad or a USB handset, gated by the pilot-in-command (PIC) arbiter.
`inject`	Channel values set by software through `POST /api/v1/ground-station/crsf/channels`. Each write carries a time-to-live.
`hybrid`	The PIC holder decides: while a client holds PIC the lane obeys that client’s source; with a fresh “no claim held” report, injected values feed. If the arbiter stops reporting, the lane falls back to the human path.

A hobby handset running EdgeTX in “USB Joystick (HID)” mode works as a hid source: its own radio is off, and the ground station’s module does the transmitting. Neither source can hold a stale stick. When the winning source has no fresh sample, the lane stops sending RC frames, so the receiver and the flight controller run their own configured RC-loss failsafe. The lane never substitutes neutral values.

Enable the lane

The lane is opt-in and runs only on the ground_station profile; on a drone it idles. Set the radio.crsf block in /etc/ados/config.yaml:

radio:
  crsf:
    enabled: true
    device: /dev/ttyUSB0
    mode: crsf_rc
    channel_source: hid
    band: dual
    packet_rate_hz: 150

device must name the module’s serial port; the lane never probes for one, and a pinned device is kept out of flight-controller discovery. enabled also writes the /etc/ados/crsf-enabled marker that the ados-crsf unit starts on. The radio keys, including every radio.crsf key with its default and allowed values:

Key	Type	Default	Allowed	Description
`radio.adapters`	array	`[]`	n/a	Adapters
`radio.adapters[].antenna`	string\|null	n/a	n/a	Antenna
`radio.adapters[].match.mac`	string\|null	n/a	n/a	Mac
`radio.adapters[].match.usb_path`	string\|null	n/a	n/a	Usb Path
`radio.adapters[].role`	string	n/a	`"rxtx"`, `"rx"`, `"tx"`, `"mesh"`	Role
`radio.crsf.band`	string	`"dual"`	`"dual"`, `"900"`, `"2p4"`	Band
`radio.crsf.channel_source`	string	`"hid"`	`"hid"`, `"inject"`, `"hybrid"`	Channel Source
`radio.crsf.device`	string\|null	n/a	n/a	Device
`radio.crsf.enabled`	boolean	`false`	n/a	Enabled
`radio.crsf.mavlink_command_enabled`	boolean	`false`	n/a	Mavlink Command Enabled
`radio.crsf.mavlink_transport`	string	`"serial"`	`"serial"`, `"backpack_wifi"`	Mavlink Transport
`radio.crsf.mode`	string	`"crsf_rc"`	`"crsf_rc"`, `"mavlink"`, `"airport"`	Mode
`radio.crsf.modules`	array	`[]`	n/a	Modules
`radio.crsf.modules[].id`	string	n/a	n/a	Id
`radio.crsf.modules[].link`	string\|null	n/a	n/a	Link
`radio.crsf.modules[].port`	string	n/a	n/a	Port
`radio.crsf.modules[].role`	string	`"pilot"`	`"pilot"`, `"autonomy"`	Role
`radio.crsf.packet_rate_hz`	integer	`150`	0 to 65535	Packet Rate Hz
`radio.crsf.relay_role`	string	`"none"`	`"none"`, `"repeater"`, `"agent_last_mile"`	Relay Role
`radio.crsf.tx_power_dbm`	integer\|null	n/a	-128 to 127	Tx Power Dbm
`radio.tunnel.command_enabled`	boolean	`false`	n/a	Command Enabled
`radio.tunnel.enabled`	boolean	`false`	n/a	Enabled
`radio.tunnel.rx_port`	integer	`5820`	0 to 65535	Rx Port

relay_role is a label the lane reports on its status; it does not change what the lane transmits.

Surfaces

Surface	Use
Mission Control	The RC / ELRS Link tab of the ground station’s node panel appears when a CRSF module is present.
`GET /api/v1/ground-station/crsf`	Lane state, mode, channel source and link statistics.
`POST /api/v1/ground-station/crsf/channels`	Inject channel values (`inject` and `hybrid` sources).
`POST /api/v1/ground-station/crsf/params`	Send parameter requests to the module.

The lane reports a link state like any other radio. Its state reads up only on received link statistics from the module, never on bytes sent. It carries no routed IP traffic and is not an internet uplink.

Bands

Band	Trade-off
900 MHz	More range, lower MAVLink throughput
2.4 GHz	More MAVLink throughput, less range
Dual-band	Both, on a dual-band module

Range depends on the module, the antennas, the band and line of sight. The lane makes no fixed range claim.

Get started

Connect your devices

At the ground station

Mesh and distributed receive

Network and fleet

Diagnose

Modes

Channel sources

Enable the lane

Surfaces

Bands

Next steps

HDMI kiosk

Ground station node panel

​Modes

​Channel sources

​Enable the lane

​Surfaces

​Bands

​Next steps

HDMI kiosk

Ground station node panel

Modes

Channel sources

Enable the lane

Surfaces

Bands

Next steps