Channel Output Functions

All servo outputs may be mapped to any function supported by ArduPilot. The default settings are for the first 4 channels to be Aileron, Elevator, Throttle and Rudder (commonly known as AETR), but you can re-assign them as needed.

This page describes how to configure these output channels and what each of the available functions is.

The SERVOn_FUNCTION parameters

In the advanced parameter view of your GCS you will find that each SERVO output channel has a SERVOn_FUNCTION parameter. For example, SERVO5_FUNCTION controls the output function of channel 5, SERVO6_FUNCTION controls the output function of channel 6 and so on.

The values you can set these parameters to are shared with copters and rovers, and not all of them have been implemented on fixed wing aircraft. The ones that are implemented on fixed wing are listed below:

  • Disabled=0
  • RCPassThru=1
  • Flap=2
  • Flap_auto=3
  • Aileron=4
  • mount_pan=6
  • mount_tilt=7
  • mount_roll=8
  • camera_trigger=10
  • mount2_pan=12
  • mount2_tilt=13
  • mount2_roll=14
  • DifferentialSpoilerLeft1=16
  • DifferentialSpoilerRight1=17
  • DifferentialSpoilerLeft2=86
  • DifferentialSpoilerRight2=87
  • Elevator=19
  • Rudder=21
  • FlaperonLeft=24
  • FlaperonRight=25
  • GroundSteering=26
  • ParachuteRelease=27
  • QuadPlaneMotor1=33
  • QuadPlaneMotor2=34
  • QuadPlaneMotor3=35
  • QuadPlaneMotor4=36
  • QuadPlaneMotor5=37
  • QuadPlaneMotor6=38
  • QuadPlaneMotor7=39
  • QuadPlaneMotor8=40
  • MotorTilt=41
  • RCPassThru1=51
  • RCPassThru2=52
  • RCPassThru3=53
  • RCPassThru4=54
  • RCPassThru5=55
  • RCPassThru6=56
  • RCPassThru7=57
  • RCPassThru8=58
  • RCPassThru9=59
  • RCPassThru10=60
  • RCPassThru11=61
  • RCPassThru12=62
  • RCPassThru13=63
  • RCPassThru14=64
  • RCPassThru15=65
  • RCPassThru16=66
  • Ignition=67
  • Starter=69
  • Throttle=70
  • ThrottleLeft=73
  • ThrottleRight=74
  • TiltMotorLeft=75
  • TiltMotorRight=76
  • ElevonLeft=77
  • ElevonRight=77
  • VTailLeft=79
  • VTailRight=80

The default values for the first 4 channels are Aileron, Elevator, Throttle and Rudder. The default for all other channels s is 0, meaning disabled. A disabled channel will output the trim value for that channel (for example, if SERVO5_FUNCTION is 0 then channel 5 will output SERVO5_TRIM) unless it is overridden by a mission command.

All of these functions may be used on multiple channels. So if you want 3 elevator channels for some reason you can set SERVOn_FUNCTION to 19 on 3 of your output channels.

Disabled

For normal operation, the Disabled output function sets the output value of the channel to the trim value. The exception to this is when a MAVLink override of the channel or a mission servo set is used. So in some ways “disabled” could be called “mission-controlled”.

When you fly an auto mission you can ask for a servo to be set to a value as part of that mission. In that case you should set the SERVOn_FUNCTION for that channel to Disabled, so that the value doesn’t get changed by another output function immediately after the mission sets the value.

RCPassThru

Setting a channel to RCPassThru means it will output the value that is coming into the board from the corresponding input channel. For example, if SERVO5_FUNCTION is 1 (meaning RCPassThru) then channel 5 output will always be equal to channel 5 input.

Flap

When a channel is set as a flap it’s value comes from the flap input channel (controlled by the FLAP_IN_CHANNEL parameter). The reason you may want to use this instead of a RCPassThru is that you can setup multiple flap channels with different trims and ranges, and you may want to take advantage of the FLAP_SLEWRATE to limit the speed of flap movement.

Flap_auto

The flap auto output function behaves like the Flap output, except it can also accept automatic flap output from the TKOFF_FLAP_PCNT and LAND_FLAP_PERCNT parameters, as well as the FLAP_1_SPEED, FLAP_1_PERCNT, FLAP_2_SPEED and FLAP_2_PERCNT parameters.

If you have both a FLAP_IN_CHANNEL set and a Flap_auto output function set then the amount of flap applied is the higher of the two.

Aileron

The aileron output function adds additional aileron outputs, with separate per-channel trim and range. This is useful when you want to trim each aileron separately, or if your main aileron is setup as an elevon mixer (using the ELEVON_OUTPUT option), and you also want some normal ailerons.

Mount_pan, Mount_tilt and Mount_roll

These control the output channels for controlling a servo gimbal. Please see the camera gimbal configuration documentation for details.

The Mount2_pan, Mount2_tilt and Mount2_roll options are the same, but control a second camera gimbal

Camera_trigger

The Camera_trigger output function is used to trigger a camera with a servo. See the camera gimbal documentation for details.

Elevator

The elevator output function adds additional elevator outputs, with separate per-channel trim and range. This is useful when you want to trim each elevator separately, or if your main elevator is setup as an elevon mixer (using the ELEVON_OUTPUT option), and you also want some normal elevator.

Rudder

The rudder output function adds additional rudder outputs, with separate per-channel trim and range. Separate rudder channels is particularly useful for nose wheel steering where the nose wheel may need to be reversed as compared to the normal rudder channel or for multi-wheel planes.

GroundSteering

The GroundSteering output function acts much like the rudder output function except that it only acts when the aircraft is below GROUND_STEER_ALT altitude. At altitudes above GROUND_STEER_ALT the output will be the trim value for the channel.

Flaperon1 and Flaperon2

Using the flaperon1 and flaperon2 output functions you can setup flaperons, which are ailerons that double as flaps. They are very useful for aircraft which have ailerons but no flaps.

See the flaperon guide for more details.

Note that flaperons act like Flap_auto described above for the flap component of the output.