ArduPilot setup checklist

This is a short guide for setting up ArduPilot on a flying wing. I use an Omnibus F4 that was previously set up for INAV (so motor on 1, elevons on 3/4), so most of this guide will be geared to that. If you use a different controller, your mileage may vary.

You should keep the full list of ArduPilot parameters open, for your reference while tuning.

Helper utility

I have created a utility that lets you easily get/set/backup/restore parameters from the command line. It’s called Parachute, and you can download it here:

https://gitlab.com/stavros/parachute

Building ArduPilot

See Building ArduPilot for instructions on how to build the latest version.

Hardware setup

The values in this section are specific to the Omnibus F4, but the settings aren’t, so you’ll usually need to adjust your outputs to your specific configuration but you probably won’t need to skip many of the steps here.

  • Connect GPS to UART 6 (SERIAL4). You don’t need to do anything else for GPS, it should work out of the box. If it doesn’t, set SERIALn_PROTOCOL=5.
  • Change the FC’s orientation with AHRS_ORIENTATION and monitor the artificial horizon to see if it moves correctly.
  • Make sure the artificial horizon is level when the plane is level on the ground. Use the β€œcalibrate level” button or AHRS_TRIM_Y to correct it if it’s not.
  • Calibrate the accelerometer. β€œForward” here needs to be the forward direction of the plane, not the arrow on the FC.
  • Connect Fport to a UART. I chose UART 3 (SERIAL2). If you want to use UART 1, you should set the RC input jumper to PPM on the F4 to disconnect the SBUS inverter from the pin.
  • To get Fport working with UART 3, you need to set BRD_ALT_CONFIG=1, to get UART 3 to act like a UART instead of I2C on the Omnibus F4.
  • Set the following for Fport on UART 3: 
    SERIAL2_PROTOCOL=23  # RCIN
SERIAL2_BAUD=115
SERIAL2_OPTIONS=4
RSSI_TYPE=3
  • Once Fport works, reverse the elevator with RC2_REVERSED=1.
  • Set up your servo functions and trims: 
    SERVO1_FUNCTION=70  # Throttle
SERVO1_MIN=1000
SERVO1_MAX=2000
SERVO1_TRIM=1000

SERVO3_FUNCTION=77  # Left elevon
SERVO3_MIN=1000
SERVO3_MAX=2000
SERVO3_TRIM=1500

SERVO4_FUNCTION=78  # Right elevon
SERVO4_MIN=1000
SERVO4_MAX=2000
SERVO4_TRIM=1500
    All these values are necessary, because usually the SERVOn_TRIM won’t be at 1500.
  • Switch to FBWA and validate that the control surfaces move correctly. If they don’t, set SERVOn_REVERSED=1. It needs to be FBWA and not MANUAL because FBWA has some additional processing like PIDs, etc.
  • Set SERVO_BLH_OTYPE=4 for DShot150 and SERVO_BLH_MASK=1 to enable it for the motor.
  • Set COMPASS_ENABLE=0 if you don’t have a compass, otherwise calibrate it (not detailed here).
  • Set TERRAIN_ENABLE=0 to get rid of the terrain warning.
  • Set the FC’s pitch relative to the body with AHRS_TRIM_Y and check that FBWA mode flies level.
  • If you don’t use logging, set LOG_BACKEND_TYPE=0. If you do use logging, set LOG_DISARMED=1 LOG_FILE_DSRMROT=0 to prevent the EKF from diverging and causing problems on takeoff.
  • Check the preflight errors to warn on, though usually leaving it set to β€œall” is fine.
  • Set up the OSD (Mission Planner has a very nice UI for that). Keep in mind that ArduPilot’s airspeed and windspeed estimation are quite good, so you may want to add those even if you don’t have an airspeed sensor. You may also want to set up multiple screens, I use a potentiometer to switch between the four different screens of the OSD:
    • One with everything on (for debugging), which is also set as the OSD_ARM_SCR/OSD_DSARM_SCR.
    • One with the artificial horizon, system messages and some basic info like RSSI, battery, ground speed and altitude.
    • A minimal screen with just system messages and battery/RSSI/speed/altitude.
    • A screen with just system messages, for when I want to enjoy the scenery.
  • Set your radio channels to AETR and run the radio calibration in the calibration section of ArduPilot.
  • Add a killswitch to the radio that overrides the mode to manual and the throttle to 0. This way it’s really easy to kill the motor right away, but you still need to go through the arming procedure to get the motor running (thanks to Michel Pastor for this great idea).
  • Set up modes, possibly having switches override the mode channel to the mode you want.
    What I do is set a given channel as the mode channel, and make that channel always output -100% on the radio. Then, I set up channel overrides for each switch, keeping in mind that overrides in OpenTX are executed in order (so the bottom override has the highest priority).
    That way, I set MANUAL/ACRO/FBWA to be lowest priority (on the same switch), then CRUISE to override those, then LOITER, RTL in that order. Finally, I add AUTO to a switch on its own channel.
    Keep in mind that whatever mode you have on its own channel might be overridden if you flick a different switch.

Auto modes

  • Set SERVO_AUTO_TRIM=1 so the aircraft trims itself while flying.
  • Set FS_SHORT_ACTN/FS_SHORT_TIMEOUT/FS_LONG_ACTN/FS_LONG_TIMEOUT. I tend to disable the short action and set long to RTL.
  • Set FLIGHT_OPTIONS+=16 so the aircraft climbs first before starting to return to home.
  • Change AUTOTUNE_LEVEL according to how aggressive you want the tune.
  • Set ACRO_PITCH_RATE/ACRO_ROLL_RATE according to your craft.
  • Set THR_PASS_STAB=1 so you have total throttle control in ACRO/FBWA/STABILIZE.
  • Set ARSPD_FBW_MIN/ARSPD_FBW_MAX to the minimum and maximum airspeed you want auto modes to fly (see the TECS tuning guide below for details).
  • Set MIN_GNDSPD_CM=833 (30 km/h) so the craft makes an effort to return even under high winds.
  • Set RTL_SINK_MAX=2 to enable a very slow descent on RTL (you generally don’t need to descend fast on RTL).

Auto takeoff

  • Change TKOFF_THR_MAX to the desired max takeoff throttle.
  • Change TKOFF_ALT to the altitude you want takeoff to reach.
  • Set THR_SUPP_MAN=1 so you can manually set the autolaunch β€œidle” throttle (before the throw).
  • Set TKOFF_THR_MINACC=18 for the takeoff throw to activate takeoff with a minimum of 2g.
  • Set TKOFF_LVL_PITCH to your desired angle (20 is a good value).
  • Set TKOFF_THR_DELAY to the number of deciseconds that you want the motor to wait before it starts up.
  • Set FLIGHT_OPTIONS+=64 so the aircraft doesn’t oscillate on auto takeoff without an airspeed sensor.
  • Potentially set TKOFF_THR_SLEW=-1 to make the throttle spin up faster.

See the recommended settings page for other recommended defaults.

In the field

  • Run an autotune.
  • Fly in FBWA and see if you’re gaining/losing altitude. Pitch up/down to fly level, check the pitch on the OSD, and use the formula old_value+pitch*Ο€/180 to get the new value for AHRS_TRIM_Y (in radians).
  • After you set AHRS_TRIM_Y correctly above, fly in FBWA at full throttle (or whatever throttle you feel is β€œfull” enough, and note that value), and note the pitch you need so that the wing doesn’t climb or sink. Then, set KFF_THR2PTCH with the formula pitch_value_in_deg * 100 / throttle_percentage. pitch_value_in_deg should be positive if you needed up pitch and negative if you needed down pitch.

(Many thanks to Michel Pastor and mfoos for their help with everything in this note.)

Last updated on April 15, 2023. For any questions/feedback, email me at hi@stavros.io.