> For the complete documentation index, see [llms.txt](https://px4.gitbook.io/px4-user-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://px4.gitbook.io/px4-user-guide/drone_parts/companion_computer.md).

# Companion Computers

Companion computers ("mission computers"), are separate on-vehicle computers that are connected to the flight controller, and which enable computationally expensive features like [object avoidance](/px4-user-guide/drone_parts/companion_computer/computer_vision/obstacle_avoidance.md) and [collision prevention](/px4-user-guide/drone_parts/companion_computer/computer_vision/collision_prevention.md).

The diagram below shows a possible architecture for an unmanned vehicle architecture that includes a flight controller and companion computer.

![PX4 architecture - FC + Companion Computer](https://4155462212-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LArEa7z2SPawfl3HpCD%2Fuploads%2Fgit-blob-f3c992ae29e4ecfea94457ddadd00283f1e09129%2Fpx4_companion_computer_simple.svg?alt=media)

The flight controller runs PX4 on NuttX, and provides core flight and safety code. The companion computer usually runs Linux, as this is a much better platform for "general" software development. They are connected using a fast serial or Ethernet link, and typically communicate using the [MAVLink protocol](https://mavlink.io/en/) or uXRCE-DDS.

Communications with the ground stations and the cloud are usually routed via the companion computer (e.g. using the [MAVLink Router](https://github.com/mavlink-router/mavlink-router)).

## Integrated Companion/Flight Controller Boards

Controller boards that come with a pre-integrated companion computer and flight controller can significantly ease both software and hardware setup. In some cases the boards are set up to allow easy replacement of flight controller and/or companion computer parts.

The following boards are known to provide a good integration with PX4:

* [Holybro Pixhawk RPI CM4 Baseboard](/px4-user-guide/drone_parts/companion_computer/holybro_pixhawk_rpi_cm4_baseboard.md)

## Managed Integrated Systems

The following integrated companion computer/flight controller systems use managed/custom versions of flight controller and companion computer software by default. They are listed here as they can be updated with "vanilla" PX4 firmware for testing/rapid development.

* [Auterion Skynode](/px4-user-guide/drone_parts/companion_computer/auterion_skynode.md)

## Companion Computer Options

PX4 can be used with computers that can be configured to communicate via MAVLink or microROS/uXRCE-DDS over over a serial port (or Ethernet port, if present).

A small subset of possible alternatives are listed below:

* Raspberry Pi
* Odroid
* Tegra K1

:::note The choice of computer will depend on the usual tradeoffs: cost, weight, power consumption, ease of setup, and computational resources required. :::

## 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.

#### Drone Apps

Drone APIs and SDKs allow you to write software that can control PX4. Popular alternatives include:

* [MAVSDK](https://mavsdk.mavlink.io/main/en/index.html) - libraries in various programming languages to interface with MAVLink systems such as drones, cameras or ground systems.
* [ROS 2](/px4-user-guide/robotics/ros/ros2.md) to communicate to ROS 2 nodes (may also be used).
* [ROS 1 and MAVROS](/px4-user-guide/robotics/ros/ros1/mavros_installation.md)

MAVSDK is generally easier to learn and use, while ROS provides more pre-written software for advanced cases like computer vision. [Drone APIs and SDKs > What API Should I Use?](/px4-user-guide/robotics.md#what-api-should-i-use) explains the different options in detail.

You can also write your own custom MAVLink libraries from scratch:

* [C/C++ example code](https://github.com/mavlink/c_uart_interface_example) shows how to connect custom code
* MAVLink also can also be used with [many other programming languages](https://mavlink.io/en/#mavlink-project-generatorslanguages)

#### Routers

You will need a router if you need to bridge MAVLink from the vehicle to a ground station or IP network, or if you need multiple connections:

* [MAVLink Router](https://github.com/intel/mavlink-router) (recommended)
* [MAVProxy](https://ardupilot.org/mavproxy/)

## Ethernet Setup

Ethernet is the recommended connection, if supported by your flight controller. See [Ethernet Setup](/px4-user-guide/advanced_config/ethernet_setup.md) for instructions.

## Flight Controller Specific Setup

The following topics explain how to set up companion computers for specific flight controllers, in particular when you are not using an Ethernet connection.

* [Using a Companion Computer with Pixhawk Controllers](/px4-user-guide/drone_parts/companion_computer/pixhawk_companion.md)

## Additional Information

* [Companion Computer Peripherals](/px4-user-guide/drone_parts/companion_computer/companion_computer_peripherals.md)
* [PX4 System Architecture > FC and Companion Computer](/px4-user-guide/development/concept/px4_systems_architecture.md#fc-and-companion-computer)