Sunday 25 June 2023

Simplified INAV

How to simplify INAV model setup and start flying sooner.

The key to simplicity is having a plane that is trimmed and balanced well mechanically, and not starting with the confusing AUTO modes. With INAV 6.1.1 the default tuning PIFFs (stabilisation parameters) will be OK for most normal performance planes.

Auto Launch, Auto Tune, Auto Trim and Missions will greatly complicate your first INAV experience. It is much simper to get the model flying well first then add the fancy stuff later.

This article is intended for fixed wing pilots who know how to mechanically set up a model for correct throws, trims and CG. 

Start with an easy to fly model that has adjustable push rods.

Important first step 

Before you install the flight control board, adjust the pushrod lengths and connection holes to give reasonable throws. This can be done with a servo checker or using your radio and PWM receiver. 

Aim for reasonable throws using 100% servo travel because INAV manual mode uses 100% weight and 30% expo by default

Then fly the model to check aileron and elevator trims and CG placement. To adjust trims you need to land and adjust the pushrod lengths mechanically without touching the radio trims.  

Radio trims should never be used in INAV because they will be ignored in stabilised modes but active in manual mode.

Doesn't have to be perfect and it's OK if the plane is a little too agile with these full throws, as long as it is flyable.

Once the trims are close to correct you can enable "Continuously trim servos" in the Configuration page. This will continuously save fine adjustments to the servo midpoints for level flight in Manual.

Essential INAV Modes

The only modes you need to set up initially are ACRO, RTH, MANUAL and ANGLE 

ACRO is the default INAV mode and is active if no other mode is selected. In ACRO the plane is stabilised against any un-commanded rotations, like a side gust of wind. The model will tend to hold its attitude but respond normally to your stick inputs. ACRO is arguably the best general flying mode.

MANUAL is a mode that has to be selected, it is not the default mode. No mode means ACRO, not Manual. MANUAL is used to check trim and CG balance, and for safety if something is wrong with other modes. Experienced pilots may prefer to fly in MANUAL mode.

ANGLE is the fully self levelling stabilised mode. It is a mode by itself, but it is also active when any of the nav or GPS modes are used. In this simplified INAV setup it is also used to check board pitch trim. Model airplanes usually need a few degrees of nose-up angle of attack to maintain level flight. This trim setting can be found in the PIDS page - Mechanics Tab - LEVEL TRIM (deg). I usually start with +4 degrees then check if the plane is rising or descending in ANGLE mode and adjust as required.

Flying in ANGLE mode may feel odd to experienced pilots because you have to hold the sticks at the angle you want to fly at and it will self level when you centre the sticks. 

RTH mode uses GPS data to automatically fly the model back to the home location. It can also be set as the Failsafe action, to bring the model back home if RC signal is lost. In the INAV Failsafe screen choose RTH.

The above modes are all you need for a basic setup

Non-essential INAV modes to add once you have a working model

NAV LAUNCH is fun to play with but I prefer to launch normally with full control. It is easy to muck up the switch sequence and cause a failed launch. 

CRUISE and LOITER modes are useful for FPV flights but not essential.

AUTO TUNE / AUTO TRIM are not required if your model is mechanically trimmed with correct CG.

Mode switches

It is best to have your starting switch positions with no modes selected, which means the board will always start in ACRO

Here are my modes for the simple setup

CH 5 (2 position) Nothing - ARM (essential for ELRS receivers)

CH 6 (3 position) Nothing - ANGLE - MANUAL

CH 7 (2 position) Nothing - RTH

Add the fancy modes later

CH 8 (3 position) Nothing - NAV CRUISE - NAV LOITER

Note that when all switches are in the "Nothing" range the board will be in ACRO 


Check the control surfaces are responding correctly to stick movements. Do the High 5 check.

Check the control surfaces are responding correctly for stabilisation. Switch to Angle Mode and check Left wing lifted makes left aileron raise and right aileron go down, tail lifted makes elevator raise.

ACRO Throws

Check the control surface throws in ACRO Mode. They may be too small for sufficient control. Ideally they should be about 80% of the Manual Mode throws. If the throws are too small go to the PID Tuning page and increase the FF parameter for Roll and Pitch, then check throws again. If there is no difference between ACRO and MANUAL Mode throws reduce the FF parameters. 

This will ensure you have enough control to launch in ACRO Mode and some headroom for stabilisation.

First Flight adjustments

On the first flight I will launch in ACRO and fly a few circuits to make sure the plane is flying OK. 

Switch to ANGLE mode. Take note of whether the model holds altitude or climbs or descends. If you haven't entered anything in the Fixed Wing Level Trim window then the plane will most likely descend.

I usually start with +4ยบ and adjust more or less from there.

Launch again, climb to about 50m, fly out a bit then try RTH. Your model should turn and fly back to the arming site and circle above you at about 50m altitude and radius of 75m.

If that all works then you are ready to continue your INAV adventure.

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