# Offboard Control


Offboard control 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 (opens new window) and the SET_ATTITUDE_TARGET (opens new window) messages.

# Offboard Control Firmware Setup

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

# Map an RC switch to offboard mode activation

To do this, load up the parameters in QGroundControl and look for the RC_MAP_OFFB_SW parameter to which you can assign the RC channel you want to use to activate offboard mode. It can be useful to map things in such a way that when you fall out of offboard mode you go into position control.

Although this step isn't mandatory since you can activate offboard mode using a MAVLink message. We consider this method much safer.

# Enable the companion computer interface

Enable MAVLink on the serial port that you connect to the companion computer (see Companion computer setup).

# 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:

Mermaid graph: mavlink channel (opens new window)

# On-board processor

A small computer mounted onto the vehicle connected to the autopilot through a UART to USB adapter. 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.

Small low power examples:

Larger high power examples:

Mermaid diagram: Companion mavlink (opens new window)

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 (opens new window)