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Inav setup for flying wings

Here we will detail the setting up of Inav for flying wings using the Inav FC we stock which has a M8n GPS module included. There are other FCs that are compatible and can be used, including the Matek F405 OSD however there pinout and functions may differ slightly.

Also note that the Inav FC bundle we have includes an integrated barometer, which isnt commonly found on most miniquad FCs these days.

 

Inav bundle 

 

A typical parts list for a Inav flying wing is as follows:

1 x airframe (S800 or AR wing  or Eachine Fury  or TBRC etc)

1 x miniquad motor (F80 used in this build, 2205-2408 low Kv for efficiency, high Kv for top speed)

1 x 30-45A ESC

1 x Inav compatible FC and GPS module

1 x PDB (5v minimum 2 amp regulator essential)

2 x servos (digital preferred)

1 x camera (HS11XX)

1 x Vtx and antenna

1 x receiver

1 x battery

Consumeables including glues, tapes, wire, solder, laminate, paint etc.

 

Upon opening the package you can see that the GPS module comes pre soldered to the board. 

Note the connections as Ive found it is easier to work on the FC with the GPS disconnected. For flying wings you may find the top two magnetometer connections (SCA/SDL) are unnecessary as wings can derive heading from GPS alone. They are red and white in this picture and can be removed from the FC permanently. You can leave the 3.3v white cable and 1k resistors in place incase you choose to use the magnetometer connection at a later date.

 

Also I like to add a small dab of epoxy to the USB connector. Just add a little to the top edge to reinforce it.

At this stage I like to modify the board so that it can tolerate higher voltages. To do this we will remove/disconnect the linear regulator on the underside. Cutting the two legs is sufficient enough but you can go further and remove it entirely. This means we will need to power the board with an external 5v regulator to the motor pins, as it will no longer power off vbatt alone.

 

Next I add a jumper across from the motor pins to the 5v rail on the other side. Below is a pic followed by a schematic of the FC that you can use throughout this post.

 

The board is an Omnibus F3 and the first thing we will do is flash Inav onto it and do some calibrations. Download the Inav configurator and plug in your FC. Select the correct COM port in the top right hand corner and enter the firmware flasher.

Once inside select the OMNIBUS board and the most recent release (1.8 at the time of writing). Hit Flash Firmware. Once this is completed you can go back to the welcome tab and click CONNECT. Those of you who are familiar with Cleanflight or Betaflight will recognise the next screen, along with a number of new tabs.

 

The board comes setup for quadcopter flight so the first thing we need to do is change it to the type of craft we are flying. For those of you who are setting it up for an AR wing you can simply dump this file into the CLI and type save.

AR wing CLI dump

I recommend reading through the INAV wiki for flying wings which can be found here. Take note of the calibration procedure as it require a 6 point calibration which is different from Betaflight.

Connections to the FC are fairly straight forward. 

ESC signal wire will connect to Motor 1

Servo signal wires connect to M3/M4, the picture in the Configuration tab will assist you in determining which servo connects to which port (make sure you have selected Flying wing.

Before gluing servos in you need to center them and attach the servo horns. A servo tester is a good way to do this. It is likely that one of the horns will be slightly off when compared to the other one, we will adjust this out in the control linkages.

Connect your servo power lines directly to your 5v regulator, or if you are using the same 5v reg to power your FC you can connect them to the FCs 5v rail.

Using the FC allows you to run PPM, SBUS or Crossfire protocols, which means you will only need 3 to 4 wires connected to your receiver. Wire your receiver to the appropriate UART port and turn on the serial switch in the Ports tab in INAV. Then dont forget to set your receiver type in the Configuration menu as well.

You can also now connect your GPS to its UART port and switch it on in the ports tab. 

Check your servos are responding correctly by doing a hi five test. You will most likely have to reverse one of them in the servo tab by changing the value to a negative number, though if you have used the dump file above it should be correct already.

Dont make any changes on your TX, your TX must be in quadcopter mode and use no mixing for this to work correctly.

 

In your first flight you want to check that the craft is flying level. There are two things that need to be checked. First and perhaps easiest is to trim your control surfaces for level flight. Ideally you will attempt to get it flying level by trimming them mechanically first, however if you find that its out of alignment in flight you can set one of your switches to trim your servo midpoints for straight flight. 

The procedure is as follows.

  1. This is intended to use in air.
  2. Fly straight, choose what mode that suites you best. (passthrough, angle or acro)
  3. Enable SERVO AUTOTRIM mode, and keep flying straight for 2 seconds. After 2 seconds it will set new midpoints based on average servo position during those 2 seconds.
  4. If your are NOT happy with new midpoints disable SERVO AUTOTRIM mode and it will revert back to old settings. If you want to keep new midpoints keep SERVO AUTOTRIM turned on, land aircraft and disarm. New midpoints will be saved.

This method can be used any time to readjust servo midpoints during flight.

 

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