Companion Computer
A companion computer (Raspberry Pi, Jetson, and similar) runs higher-level software next to the flight controller: computer vision, mapping, mission logic, or ROS 2. The 305ap connects to it over TELEM 2 (recommended) or USB.
Connecting over TELEM 2
TELEM 2 (CN3, UART7) has RTS/CTS flow control and defaults to 921600 baud, which suits a companion link.
| 305ap pin | Connect to companion |
|---|---|
| 2 TX | UART RX |
| 3 RX | UART TX |
| 4 CTS | RTS (if available) |
| 5 RTS | CTS (if available) |
| 6 GND | GND |
Pin 1 (+5V) is an output from the flight controller. Don't connect it to the companion's 5 V.
The companion's UART must be 3.3 V logic. A USB-to-serial adapter (FTDI or similar) at 3.3 V also works.
MAVLink (MAVSDK, MAVROS)
Set in QGroundControl and reboot:
| Parameter | Value |
|---|---|
MAV_1_CONFIG | TELEM 2 |
MAV_1_MODE | Onboard (default) |
SER_TEL2_BAUD | 921600 (default) |
MAV_1_FLOW_CTRL | Force on (1) if RTS/CTS are wired, otherwise Force off (0) |
On the companion, connect your MAVLink software to the serial device at 921600 baud, for example serial:///dev/ttyAMA0:921600 in MAVSDK.
ROS 2 (uXRCE-DDS)
The firmware includes PX4's uXRCE-DDS client, which publishes PX4 topics directly to ROS 2.
| Parameter | Value |
|---|---|
UXRCE_DDS_CFG | TELEM 2 |
SER_TEL2_BAUD | 921600 |
Then run the agent on the companion:
MicroXRCEAgent serial --dev /dev/ttyAMA0 -b 921600
Use either MAVLink or uXRCE-DDS on TELEM 2, not both. See the PX4 ROS 2 guide for the ROS 2 side.
Connecting over USB
The companion can also use the 305ap's USB-C port. The flight controller appears as a USB serial device (/dev/ttyACM0 on Linux) carrying MAVLink.
USB from the companion also feeds the 305ap's 5 V power mux. When the battery is connected, the board's own 5 V supply normally takes over. The board can't tell whether USB is connected, and USB is less robust to vibration than a JST-GH connector, so TELEM 2 is preferred in flight.
Powering the Companion
Power the companion computer from its own regulator, not from the 305ap's 5 V pins. Companion computers can draw several amps, and their load changes constantly with CPU and radio activity. A varying load on the board's 5 V rail can throw off the onboard compass; see Magnetometer. For vehicles with a companion computer, an external GPS + compass module is recommended.
Checking the Link
In the MAVLink Console:
mavlink status # MAVLink instances, rates, flow control
uxrce_dds_client status # if using ROS 2