Autopilot parameters can be set in the groundstation and provide an easy way to tune the behavior of the firmware for your purposes. Typical parameters are the PID gains of the controllers. Others include the flight environment, calibration information (sensor offsets) and so on.

It is possible to tune the parameters in flight (e.g. PID gains), but it is only recommended if you absolutely know what you are doing. The controller apps (attitude control, position control) update their internal copy of the PID gains periodically.

A list of all on-board parameters can be found on this page: Parameter Reference

1. Make sure you have the Calibration and On-board Parameters widget visible in QGroundControl (menu bar/Tool Widgets/Calibration and Parameters).
2. Make sure you are connected to the FMU.
3. If you are connected, there should be a list with the current parameter values visible. If this is not the case, press Refresh.
4. Change the parameters' values.
5. Press Set.
6. If you are happy with the new parameter and want to save it permanently, press Write (ROM).

Binding a parameter to a potentiometer knob on your RC is handy for tuning control gains. You will need at least 1 unused channel on you receiver. If you only have 8 channels in total you can map the switches to one channel on your RC to free up 3 channels. PX4 supports mapping up to 3 knobs to a parameter.

The following sequence describes the setup for one channel.

1. Find the RC channel which your knob is controlling with the help of the RC Calibration tool in the Setup view
2. Set the parameter `RC_MAP_PARAM1` (or 2/3) to the value obtained in 1 as described in 'How to set a parameter using QGroundControl' (don't forget to press Write (ROM))
3. Make sure the knob on your RC is centered and the value visible in the RC Calibration tool in the Setup view is centered as well
4. Now right-click on the parameter which you want to bind to the knob and select Map Parameter to RC
5. In the dialog configure the values to your liking: The parameter value is given by:

   constrain(initial_value + scale * RC_value, minimum, maximum)

   where

   -1 <= RC_value <= 1

   is the position of your knob. Hit OK to activate the mapping on the AUtopilot .

6. When you turn your knob every second the parameter will be updated to the value defined by the RC knob. To get the current value right-click on the parameter and hit Refresh this param. The general idea is that you don't have to look up the value while tuning. slowly turn the knob until you are happy with the behavior.
7. If you are happy with the new parameter and want to save it permanently, press Write (ROM).

Note that if you restart the autopilot you will have to restart at step 4, as the settings are not stored for safety reasons.

Information on creating your own parameters can be found on this page.