# Offboard Control

::: warning
[Offboard control](../flight_modes/offboard.md) is dangerous.
It is the responsibility of the developer to ensure adequate preparation, testing and safety precautions are taken before offboard flights.
:::

The idea behind off-board control is to be able to control the PX4 flight stack using software running outside of the autopilot.
This is done through the MAVLink protocol, specifically the [SET_POSITION_TARGET_LOCAL_NED](https://mavlink.io/en/messages/common.html#SET_POSITION_TARGET_LOCAL_NED) and the [SET_ATTITUDE_TARGET](https://mavlink.io/en/messages/common.html#SET_ATTITUDE_TARGET) messages.

## Offboard Control Firmware Setup

There are two things you want to setup on the firmware side before starting offboard development.

### Enable Stick Override

In _QGroundControl_ the [MAN_OVERRIDE_SPD](../advanced_config/parameter_reference.md#MAN_OVERRIDE_SPD) parameter controls automatically switching from offboard (or autonomous) mode to Position mode when the remote sticks are moved. This is enabled by default; set it to -1 to disable.
This is the best way to ensure that an operator can easily take control of the vehicle and switch to the safest flight mode.

### Map an RC switch to offboard mode activation

In _QGroundControl_ you can set the [RC_MAP_OFFB_SW](../advanced_config/parameter_reference.md#RC_MAP_OFFB_SW) parameter to the RC channel that will be used to activate offboard mode.
This can be used to switch between offboard mode and the mode set by the mode switch ([RC_MAP_MODE_SW](../advanced_config/parameter_reference.md#RC_MAP_MODE_SW)).
You can also switch into offboard mode using a GCS/MAVLink so this is not "mandatory".

Note also that this mechanism is not as "safe" as using [stick Override](#enable-stick-override) to switch out of offboard mode, because the mode you switch to is unpredictable.

### Enable the companion computer interface

Enable MAVLink on the serial port that you connect to the companion computer (see [Companion Computers](../companion_computer/index.md)).

## Hardware setup

Usually, there are three ways of setting up offboard communication.

### Serial radios

1. One connected to a UART port of the autopilot
2. One connected to a ground station computer

   Example radios include:
   - [Digi International XBee Pro](https://www.digi.com/products/embedded-systems/digi-xbee/rf-modules/sub-1-ghz-rf-modules)

[![Mermaid graph: mavlink channel](https://mermaid.ink/img/eyJjb2RlIjoiZ3JhcGggVEQ7XG4gIGduZFtHcm91bmQgU3RhdGlvbl0gLS1NQVZMaW5rLS0-IHJhZDFbR3JvdW5kIFJhZGlvXTtcbiAgcmFkMSAtLVJhZGlvUHJvdG9jb2wtLT4gcmFkMltWZWhpY2xlIFJhZGlvXTtcbiAgcmFkMiAtLU1BVkxpbmstLT4gYVtBdXRvcGlsb3RdOyIsIm1lcm1haWQiOnsidGhlbWUiOiJkZWZhdWx0In0sInVwZGF0ZUVkaXRvciI6ZmFsc2V9)](https://mermaid-js.github.io/mermaid-live-editor/#/edit/eyJjb2RlIjoiZ3JhcGggVEQ7XG4gIGduZFtHcm91bmQgU3RhdGlvbl0gLS1NQVZMaW5rLS0-IHJhZDFbR3JvdW5kIFJhZGlvXTtcbiAgcmFkMSAtLVJhZGlvUHJvdG9jb2wtLT4gcmFkMltWZWhpY2xlIFJhZGlvXTtcbiAgcmFkMiAtLU1BVkxpbmstLT4gYVtBdXRvcGlsb3RdOyIsIm1lcm1haWQiOnsidGhlbWUiOiJkZWZhdWx0In0sInVwZGF0ZUVkaXRvciI6ZmFsc2V9)

<!-- original mermaid graph
graph TD;
  gnd[Ground Station] --MAVLink-- > rad1[Ground Radio];
  rad1 --RadioProtocol-- > rad2[Vehicle Radio];
  rad2 --MAVLink-- > a[Autopilot];
-->

### On-board processor

A small computer mounted onto the vehicle, connected to the autopilot through a serial port or Ethernet port.
There are many possibilities here and it will depend on what kind of additional on-board processing you want to do in addition to sending commands to the autopilot.
Some examples are provided in [Companion Computers](../companion_computer/index.md#companion-computer-options).

[![Mermaid diagram: Companion mavlink](https://mermaid.ink/img/eyJjb2RlIjoiZ3JhcGggVEQ7XG4gIGNvbXBbQ29tcGFuaW9uIENvbXB1dGVyXSAtLU1BVkxpbmstLT4gdWFydFtVQVJUIEFkYXB0ZXJdO1xuICB1YXJ0IC0tTUFWTGluay0tPiBBdXRvcGlsb3Q7IiwibWVybWFpZCI6eyJ0aGVtZSI6ImRlZmF1bHQifSwidXBkYXRlRWRpdG9yIjpmYWxzZX0)](https://mermaid-js.github.io/mermaid-live-editor/#/edit/eyJjb2RlIjoiZ3JhcGggVEQ7XG4gIGNvbXBbQ29tcGFuaW9uIENvbXB1dGVyXSAtLU1BVkxpbmstLT4gdWFydFtVQVJUIEFkYXB0ZXJdO1xuICB1YXJ0IC0tTUFWTGluay0tPiBBdXRvcGlsb3Q7IiwibWVybWFpZCI6eyJ0aGVtZSI6ImRlZmF1bHQifSwidXBkYXRlRWRpdG9yIjpmYWxzZX0)

<!-- original mermaid graph
graph TD;
  comp[Companion Computer] --MAVLink-- > uart[UART Adapter];
  uart --MAVLink-- > Autopilot;
-->

### On-board processor and wifi link to ROS (**_Recommended_**)

A small computer mounted onto the vehicle connected to the autopilot through a UART to USB adapter while also having a WiFi link to a ground station running ROS.
This can be any of the computers from the above section coupled with a WiFi adapter.

[![Mermaid graph: ROS](https://mermaid.ink/img/eyJjb2RlIjoiZ3JhcGggVERcbiAgc3ViZ3JhcGggR3JvdW5kICBTdGF0aW9uXG4gIGduZFtST1MgRW5hYmxlZCBDb21wdXRlcl0gLS0tIHFnY1txR3JvdW5kQ29udHJvbF1cbiAgZW5kXG4gIGduZCAtLU1BVkxpbmsvVURQLS0-IHdbV2lGaV07XG4gIHFnYyAtLU1BVkxpbmstLT4gdztcbiAgc3ViZ3JhcGggVmVoaWNsZVxuICBjb21wW0NvbXBhbmlvbiBDb21wdXRlcl0gLS1NQVZMaW5rLS0-IHVhcnRbVUFSVCBBZGFwdGVyXVxuICB1YXJ0IC0tLSBBdXRvcGlsb3RcbiAgZW5kXG4gIHcgLS0tIGNvbXAiLCJtZXJtYWlkIjp7InRoZW1lIjoiZGVmYXVsdCJ9LCJ1cGRhdGVFZGl0b3IiOmZhbHNlfQ)](https://mermaid-js.github.io/mermaid-live-editor/#/edit/eyJjb2RlIjoiZ3JhcGggVERcbiAgc3ViZ3JhcGggR3JvdW5kICBTdGF0aW9uXG4gIGduZFtST1MgRW5hYmxlZCBDb21wdXRlcl0gLS0tIHFnY1txR3JvdW5kQ29udHJvbF1cbiAgZW5kXG4gIGduZCAtLU1BVkxpbmsvVURQLS0-IHdbV2lGaV07XG4gIHFnYyAtLU1BVkxpbmstLT4gdztcbiAgc3ViZ3JhcGggVmVoaWNsZVxuICBjb21wW0NvbXBhbmlvbiBDb21wdXRlcl0gLS1NQVZMaW5rLS0-IHVhcnRbVUFSVCBBZGFwdGVyXVxuICB1YXJ0IC0tLSBBdXRvcGlsb3RcbiAgZW5kXG4gIHcgLS0tIGNvbXAiLCJtZXJtYWlkIjp7InRoZW1lIjoiZGVmYXVsdCJ9LCJ1cGRhdGVFZGl0b3IiOmZhbHNlfQ)

<!-- original mermaid graph
graph TD
  subgraph Ground  Station
  gnd[ROS Enabled Computer] --- qgc[qGroundControl]
  end
  gnd --MAVLink/UDP-- > w[WiFi];
  qgc --MAVLink-- > w;
  subgraph Vehicle
  comp[Companion Computer] --MAVLink-- > uart[UART Adapter]
  uart --- Autopilot
  end
  w --- comp
-->