> For the complete documentation index, see [llms.txt](https://docs.auterion.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.auterion.com/vehicle-operation/dragon-setup/dragon-mr-lr/control-surfaces-and-actuators.md).

# Control Surfaces and Actuators

To setup control surfaces and actuators follow: [**PX4 Actuator Configuration**](https://docs.px4.io/main/en/config/actuators.html).

### Control surface trims & prearm behavior

There are two ways to control the neutral position of a control surface:

* `PWM_MAIN_CENTx` / `PWM_AUX_CENTx` : always use these for PWM servos
* `CA_SV_CSx_TRIM` : use these for non-PWM servos

Whether or not the trim and center values are applied while the vehicle is disarmed is determined by the `COM_PREARM_MODE` parameter. 

* `0` Disabled: surfaces sit at their `PWM_*_DIS`  position
* `1` Safety Button: Trims are applied when a safety switch is flipped
* `2` Always: Trims are applied as soon as servos are powered

In general, we do recommend to set `COM_PREARM_MODE=Always` for easier on-ground preflight checks.