This is a short guide for setting up [ArduPilot](https://ardupilot.org/) 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](https://ardupilot.org/plane/docs/parameters.html) open, for your reference while tuning.
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`.
- [ ] 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.
- [ ] 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:
- [ ] 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.
Unfortunately, the way the mode system in AP works, there's no good way to have a list of prioritized modes, which would be ideal though now I have opened a PR to extend the modes to 12, which solves this).
- [ ] 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).
- [ ] 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*π/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 "full" enough, and note that value), and note the pitch you need so that the wing doesn't climb or sink. Then, set `KFF_THR2PITCH` 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.
