Auxiliary Functions

This feature is firmware versions 4.0 and higher. In Copter versions before 4.0 similar functions were implemented using the CHx_OPT parameters. See Auxiliary Function Switches (3.6 and earlier) page.

This page describes how to set up additional features which can be invoked from the transmitter’s auxiliary function switches.

Configuring which transmitter channel is used

Any RC input channel can be assigned any auxiliary function. However, the RC channel should not be used by any other function, such as flight mode selection or flight controls. By default, channels 1-4 are used for flight controls, channel 8 is used for flight modes in Plane and Rover, as is channel 5 in Copter.

Assigning the Feature

The RCx_OPTION parameters control these features. For example, the RC7_OPTION parameter controls which feature is assigned to RC input 7. Each RC channel has its own RCx_OPTION parameter that can be accessed in the full parameter list.

Supported Features

RCx_OPTION value Feature Description Copter Plane Rover
0 Do Nothing (Default) X X X
2 FLIP X    
3 SIMPLE mode (Copter) X    
4 RTL mode X X X
5 Save Trim X   X
7 Save Waypoint X   X
9 Camera Trigger X X X
10 Rangefinder X    
11 Fence X X X
12 ResetToArmedYaw      
13 SUPERSIMPLE mode X    
14 Acro Trainer X    
15 Sprayer X    
16 AUTO mode X X X
17 AUTOTUNE mode X    
18 LAND Mode X    
19 Gripper X    
21 Parachute Enable X    
22 Parachute Release X    
23 Parachute 3 Pos Switch X    
24 Reset Auto Mission to start X X X
25 Attitude Controller FF X    
26 Attitude Controller AccLim X    
27 Retract Mount X    
28 Relay 1 On/off X X X
29 Landing Gear X X  
30 Lost Vehicle Sound X X X
31 Motor Emergency Stop X X X
32 Motor Interlock X    
33 BRAKE X    
34 Relay 2 On/Off X X X
35 Relay 3 On/Off X X X
36 Relay 4 On/Off X X X
37 THROW mode X    
38 ADSB Avoidance Enable X    
39 Precision Loiter X    
40 Object Avoidance X   X
41 Arm Disarm X X X
42 SMARTRTL mode X   X
43 Inverted Flight X X  
46 RC Override Enable X X X
47 Rsvd for custom function X    
48 Rsvd for custom function X    
49 Rsvd for custom function X    
50 Learn Cruise     X
51 MANUAL mode   X X
52 ACRO mode X   X
53 STEERING mode     X
54 HOLD mode     X
55 GUIDED mode X X X
56 LOITER mode X   X
57 FOLLOW mode X   X
58 Clear Waypoints X X X
59 SIMPLE mode (Rover)     X
60 ZIGZAG mode X    
61 ZIGZAG mode - Save Waypts X    
62 Compass Learn X X X
63 Sailboat Tack     X
64 Reverse Throttle   X  
65 GPS Disable X X X
66 Relay 5 On/Off X X X
67 Relay 6 On/Off X X X
68 STABILIZE mode X    
69 POSHOLD mode X    
70 ALTHOLD mode X X  
71 FLOWHOLD mode X    
72 CIRCLE mode X X  
73 DRIFT mode X    
74 Sailboat Motor 3Pos Sw     X
75 Surface Tracking Up/Down X    
76 STANDBY mode X    
77 TAKEOFF mode   X  
78 RunCam Control X X X
79 RunCam OSD Control X X X
80 Viso Align X    
81 Disarm X X X
82 Q_Assist 3Pos Sw   X  
83 ZIGZAG Auto X    
84 AIRMODE(not a flight mode) X X  
85 Generator X X X
86 Non Auto Terrain Follow Disable   x  
87 CROW Mode Switch   X  
88 Soaring Enable   X  
89 Force Flare   X  
90 EKF Position Source X X X
91 Airspeed Ratio Calibrate   X  
92 FBWA Mode   X  
94 VTX Power X X X
97 WindVane home dii offset     X
102 Camera Mode Toggle X X X
105 GPS Disable Yaw (testing only!) X X X

Intended as continuous PWM range control inputs:

RCx_OPTION value Feature Description Copter Plane Rover
201 ROLL Input X X X
202 PTCH Input X X X
203 THROTTLE Input X X X
204 YAW Input X X X
207 Mainsail     X
208 Flap Control   X  
209 Forward Throttle   X  
210 Airbrakes   X  
211 Walking Robot Height     X
300-307 Scripting RC channels X X X

Description of Features


in descriptions below, LOW and HIGH for a channel refers to PWM <1200us and >1800us, respectively.

Mode Switches

Any feature ending with “mode” provides the ability to switch the vehicle into that mode by setting the RC channel to high. You can have multiple “mode” option switches and more than one can be high at a time. The last “mode” change switch will determine the current mode, as well as any change of the normal mode switch.

For example, if you have a “LOITER mode” switch active and then an “AUTO mode” switch is switched high, the mode will change to AUTO. Changing the normal flight mode switch will again change the mode to the new flight mode setting, even though both RCx_OPTION mode switches are high. Lowering an active RCx_OPTION mode switch back to low, will return the flight mode to whatever is set on the flight mode channel, but only if the current mode matches the mode set by that switch. Otherwise, it will have no effect.


Copter and Rover mode changes are not guaranteed. They may be denied if the conditions required for that mode are not met. For example, changing to LOITER mode in Copter would fail if GPS lock is not active, whereas Plane will always change to the demanded mode and operate as best as it can.


If mapped to a three-position switch then the SUPERSIMPLE mode function will allow SUPERSIMPLE and SIMPLE modes to be enabled using the high and middle switch positions, respectively (a two-position switch will enable/disable SUPERSIMPLE mode only). See here for more details .

Other functions are:

Option Description

Vehicle will flip on its roll or pitch axis depending upon the pilot’s roll and pitch stick position. See Flip Mode .

Save Trim

In Rover,a high saves the current steering channel trim, see Save Steering Trim . In Copter, it adjusts the vehicle level position using the current roll and pitch stick inputs. See details here .

Save Waypoint Save the current location (including altitude) as a waypoint in the mission. If in AUTO mode no waypoint will be saved, instead the vehicle will RTL
Camera Trigger

Camera shutter will be activated. See more details here.

Range Finder

RangeFinder is disabled when switch is in low position, enabled when in high position.

Fence Fence is disabled when switch is in low position, enabled when it high position.
Acro Trainer

Turn on automatic leveling in the ACRO flight mode.


Turn on the crop sprayer when switch is pulled high.


Operates the gripper. Switch pulled low releases the gripper, high closes or grabs.

Parachute Enable

Enables the automatic release of the parachute (this does not immediately trigger the release).

Parachute Release

Immediately triggers the release of the parachute as long as the vehicle is not landed or too low.

Parachute 3Pos

Switch pulled low disables the parachute. Switch in middle enables the parachute for automatic release. Switch pulled high triggers release of the parachute as long as vehicle is not landed or too low.

Mission Reset

Reset AUTO to run the first mission command in the command list.

AttCon Feed Forward Turns on/off attitude controllers feed forward. For developers only.
AttCon Accel Limits Turns on/off attitude controller acceleration limits. For developers only.
Retract Mount

Move the camera mount to its retracted position.

Relay 1 On/Off

Switch pulled low turns off the first relay, pulled high turns on the first relay.

Landing Gear

Deploys or Retracts Landing Gear

Lost Vehicle Alarm

Plays the lost copter alarm though the buzzer

Emergency Stop Motors

Stops motors immediately (video)

Motor Interlock

Motor Interlock controls the way the heliRSC (motor throttle control) output is generated in Traditional Helicopters and HeliQuads. If > 1200us, it enables the Motor Interlock function, below it is disabled. When <1200us, it is similar to what is sometimes referred to as Throttle Hold in RC Helicopter terminology for Traditional Helicopters and HeliQuads. For Mulit-copters, it is used as a motor stop function when <1200us. (video).


Invokes the Brake flight mode when switch goes high. Bringing switch back to low will return the vehicle to the mode indicated by the ch5 flight mode switch.

Relay2 On/Off

Switch pulled low turns off the second relay, pulled high turns on the second relay.

Relay3 On/Off

Switch pulled low turns off the third relay, pulled high turns on the third relay.

Relay4 On/Off

Switch pulled low turns off the fourth relay, pulled high turns on the fourth relay.


Invokes the Throw flight mode when switch goes high. Bringing switch back to low will return the vehicle to the mode indicated by the ch5 flight mode switch.


When switch is high, ADSB avoidance (avoidance of manned aircraft) is enabled, otherwise it’s disabled

Precision Loiter

Turns on/off Precision Loiter. I.e. holding position above a target in Loiter mode using IR-Lock sensor.

Object Avoidance

When switch is high, avoid objects using Lightware SF40c or TeraRanger Tower. When low, object avoidance is disabled.


Arms the vehicle if the switch goes high (subject to arming checks). Disarms the vehicle if brought low.

Inverted Flight

Enabling inverted flight only changes how ArduPilot stabilizes the vehicle. It will stabilize it with a roll of 180 degrees from normal whenever inverted flight is enabled in a stabilized mode. Unless the vehicle is capable of inverted flight, do NOT use this option.

RC Override Enable

This is a 3 position switch which enables (high) or disables (low) the use of RC overrides from the Ground Control Station.

Learn Cruise

This starts the cruise speed and throttle learning sequence on Rover when switched to high. See Tuning Speed and Throttle .

Clear Waypoints

Clears currently loaded mission waypoints.

Compass Learn

Inflight compass offset learning. See Automatic Offset Calibration section of Advanced Compass Setup .

Sailboat Tack

Any high to low, or low to high change on this channel will start a tack with opposite direction to the last tack. See Sailboat Configuration and Setup .

Reverse Throttle

When switched high, forces throttle reverse in Plane for steepening descents. Normally, this is controlled by flight mode via the USE_REV_THRUST parameter. See Automatic Landing for more information on setup of reverse thrust.

GPS Disable

Simulates GPS failure by disabling GPS.

Relay 5 On/Off

Switch pulled low turns off the third relay, pulled high turns on the fifth relay.

Relay 6 On/Off

Switch pulled low turns off the third relay, pulled high turns on the sixth relay.

Sailboat Motor 3Pos Switch

This three position switch controls the Sailboat motor. Motor is always used when high, never used when low, and as needed, otherwise.

Surface Tracking Up/Down

This three position switch determines if surface tracking via rangefinder is toward the ground (low) or ceiling (high), or disabled, otherwise.


This puts the autopilot control loops into a soft standby mode so that a parallel, redundant autopilot or companion computer can assume control of the vehicle. The PID loops, position, altitude controllers are modified such that the autopilot can smoothly resume control of the vehicle when standby is subsequently disabled. Switching of outputs or other peripherals must be done by external circuitry.

RunCam Control

Allows starting and stopping video recording of compatible RunCam cameras. See RunCam Camera Support

RunCam OSD Control

Enables control of RunCam cameras OSDs. See RunCam Camera Support

VISO Align

Aligns external Visual Odometry with current autopilot AHRS


Disarm vehicle unconditionally and immediately. Unlike Emergency Stop Motors, which waits for DISARM_DELAY in Copter.

Q_Assist 3Pos SW

Low: disable Q_Assist entirely, Middle: Normal Q_Assist operation, High: Q_Assist active at all times. See Assisted Fixed Wing Flight section of Flying a QuadPlane

ZigZag Mode Auto Enable

Enable automatic zigzag and sprayer in ZIGZAG mode. See ZigZag Mode

AIRMODE (not a regular flight mode)

Enables and disables AIRMODE feature. See AirMode


Mode control for Richenpower Hybrid Power Generator

Non Auto Terrain Follow Disable

Disables Terrain Following in CRUISE and FBWB modes

CROW Mode Switch

Selects between different CROW aileron operating modes

Soaring Enable

Enables Soaring function operating modes

Force Flare

Moves tilt motors to upright position and optionally sets pitch for flare when landing Tilt Rotor Quadplanes. Middle: Pilot retains pitch control during flare. High: Pitch set to LAND_PITCH_CD.

EKF Position Source

Allows switching between up to three source sets manually for EKF3 (only). See GPS / Non-GPS Transitions

Airspeed Ratio Calibrate

Activates calibration of airspeed ratio in flight. Best results occur while executing course changes over 360 degrees over time, as in LOITER mode. See Calibrating an Airspeed Sensor.

VTX Power

Allows reading up to a 6 position switch for controlling Video Transmitter Power. See Smart Audio page (to be provided in the future)


Enables FBWA taildragger takeoff mode holding elevator and tail on ground until airspeed is reached


Forces mode switch to be re-read.

WindVane home direction offset

This is a continuous input channel providing a -45 to +45 degree offset the the initial wind direction when using WNDVN_TYPE = 2.

Camera Mode Toggle

Toggle camera mode (Photo/Video/etc.). Ideally, should be momentary switch since only low to high transitions toggle the camera mode. Used only with Solo gimbals presently.

GPS Disable Yaw

Disables yaw for testing (advanced users only!)

ROLL Input

ROLL input channel. (replaces RCMAP)


PITCH input channel. (replaces RCMAP)


THROTTLE input channel. (replaces RCMAP)

YAW Input

YAW input channel. (replaces RCMAP)


This RC channel will drive the output of the MainSail output ( SERVOx_FUNCTION = 89) instead of being set from the Throttle Input channel (useful if it has an auxiliary motor using that input). See Sailboat Configuration and Setup for more information about the main sail setup.


This RC channel provides manual control the amount of FLAP deflection and can also be used in conjunction with Automatic Flaps and/or flaperons . (Replaces the old FLAP_IN_CHANNEL parameter)

Forward Throttle

Manual forward motor throttle in QSTABILIZE, QACRO, and QHOVER modes


Controls deployment of Airbrakes

Walking Robot Height

Input channel for Walking Robot Height. See Walking Robots.

Scripting RC channels

Allows reading a dedicated RC channel for script inputs

Check the channel range


The configured feature will be triggered when the auxiliary switch’s pwm value becomes higher than 1800. It will be deactivated when the value falls below 1200.

You can check the pwm value sent from the transmitter when the switch is high and low using the Mission Planner’s Initial Setup >> Mandatory Hardware >> Radio Calibration screen. If it does not climb higher than 1800 or lower than 1200, it is best to adjust the servo end points in the transmitter.