# Using a Companion Computer with Pixhawk Controllers
PX4 running on Pixhawk-series flight controllers can connect to a companion computer using any free configurable serial port, including the Ethernet port (if supported).
See Companion Computers for information about supported hardware and general setup.
# Companion Computer Software
The companion computer needs to run software that communicates with the flight controller, and which routes traffic to ground stations and the cloud.
Common options are listed in Companion Computers > Companion Computer Setup.
# Ethernet Setup
Ethernet is the recommended connection, if supported by your flight controller. See Ethernet Setup for instructions.
# Serial Port Setup
These instructions explain how to setup the connection if you're not using Ethernet.
# Pixhawk Configuration
PX4 expects companion computers to connect via TELEM2 for offboard control.
The port is configured by default to interface using MAVLink.
If using MAVLink, no other PX4-side configuration should be required.
To use MAVLink on another port, and/or disable it on TELEM2, see MAVLink Peripherals (GCS/OSD/Companion) and Serial Port Configuration.
To use ROS 2/uXRCE-DDS instead of MAVLink on TELEM2, disable MAVLink on the port and then enable the uXRCE-DDS client on TELEM2(see uXRCE-DDS > Starting the client).
# Serial Port Hardware Setup
If you're connecting using a serial port, wire the port according to the instructions below. All Pixhawk serial ports operate at 3.3V and are 5V level compatible.
WARNING
Many modern companion computers only support 1.8V levels on their hardware UART and can be damaged by 3.3V levels. Use a level shifter. In most cases the accessible hardware serial ports already have some function (modem or console) associated with them and need to be reconfigured in Linux before they can be used.
A safe and easy to set up option is to use an FTDI Chip USB-to-serial adapter board to connect from TELEM2 on the Pixhawk to the USB port on the companion computer.
The TELEM2 to FTDI wiring map is shown below.
| TELEM2 | FTDI | ||
|---|---|---|---|
| 1 | +5V (red) | DO NOT CONNECT! | |
| 2 | Tx (out) | 5 | FTDI RX (yellow) (in) |
| 3 | Rx (in) | 4 | FTDI TX (orange) (out) |
| 4 | CTS (in) | 6 | FTDI RTS (green) (out) |
| 5 | RTS (out) | 2 | FTDI CTS (brown) (in) |
| 6 | GND | 1 | FTDI GND (black) |
You may also be able to directly connect TELEM2 directly to a companion computer serial port.
This is demonstrated for the Raspberry Pi in Raspberry Pi Companion with Pixhawk.
# USB Serial Port Software setup on Linux
On Linux the default name of a USB FTDI would be like \dev\ttyUSB0.
If you have a second FTDI linked on the USB or an Arduino, it will registered as \dev\ttyUSB1.
To avoid the confusion between the first plugged and the second plugged, we recommend you to create a symlink from ttyUSBx to a friendly name, depending on the Vendor and Product ID of the USB device.
Using lsusb we can get the vendor and product IDs.
$ lsusb
Bus 006 Device 002: ID 0bda:8153 Realtek Semiconductor Corp.
Bus 006 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 002: ID 05e3:0616 Genesys Logic, Inc.
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 004: ID 2341:0042 Arduino SA Mega 2560 R3 (CDC ACM)
Bus 003 Device 005: ID 26ac:0011
Bus 003 Device 002: ID 05e3:0610 Genesys Logic, Inc. 4-port hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 002: ID 0bda:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
The Arduino is Bus 003 Device 004: ID 2341:0042 Arduino SA Mega 2560 R3 (CDC ACM)
The Pixhawk is Bus 003 Device 005: ID 26ac:0011
Note
If you do not find your device, unplug it, execute lsusb, plug it, execute lsusb again and see the added device.
Therefore, we can create a new UDEV rule in a file called /etc/udev/rules.d/99-pixhawk.rules with the following content, changing the idVendor and idProduct to yours.
SUBSYSTEM=="tty", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0042", SYMLINK+="ttyArduino"
SUBSYSTEM=="tty", ATTRS{idVendor}=="26ac", ATTRS{idProduct}=="0011", SYMLINK+="ttyPixhawk"
Finally, after a reboot you can be sure to know which device is what and put /dev/ttyPixhawk instead of /dev/ttyUSB0 in your scripts.
Note
Be sure to add yourself in the tty and dialout groups via usermod to avoid to have to execute scripts as root.
usermod -a -G tty ros-user
usermod -a -G dialout ros-user