Monday, 1 July 2019

Collection of Fixed Wing iNAV tips

This page will record any clever Fixed Wing iNAV tips I pick up over time.

Most of these tips come from
Facebook iNav Fixed Wing Group
Pawel Spychalski's YouTube Channel
and some very helpful YouTube subscribers.

Transmitter Trims (Pawel)
Trims should not be used with iNav flight control boards, don't touch them.
In fact you can disable them totally
In the Taranis Flight Modes screen change all the trim values on the default flight mode FM0 from (: 0) to (- -)
The trims will disappear from the transmitter screen and no longer be active  The trim switches now can be setup as normal switches for other uses. Which is quite useful because it's easy to run out of normal mode switches on transmitters like the QX7.

Only need one model setup (Stewie - UAVFutures)
Programming setup in your transmitter is identical for all iNav models. Wings, planes and even quads need the same 4 channels and mode switches. So you only actually need one iNav Model in your transmitter. If you set the receiver number to 00 you can bind as many receivers as you need to this one OpenTX model.
You can have all the extra functions like flaps and pan/tilt programmed in and just not use them on models that don't require them.

Forget about Angle and Horizon Modes (Pawel)
Well, maybe not totally.
I never use Angle as an actual flight mode because you have to hold the stick at the angle you want the plane to maintain, and the board has to be perfectly aligned. It's a self-level mode which might appeal to beginners but to me it feels like you have to fight the board to make the plane fly where you want.
However Angle Mode is necessary to initially setup the board alignment (mainly pitch degrees) and is used automatically with the GPS modes. That's why when you select one of the GPS modes, before satellites are acquired, Angle Mode will be activated.
Angle is also useful on the bench to check that the control surfaces move in the correct direction for stabilisation.

If you want your plane to fly level without stick input use Altitude Hold. That mode uses GPS to maintain level flight and Angle Mode for stabilisation. Or even Acro mode will hold the current attitude.

PIFF (PID) Tuning (Wiki, Pawel)
Increase FF (D) until control surface movement in Acro (or Angle) is 90% of Manual Mode
This will give you all the control surface movement you need while saving some for stabilisation.
One of the biggest problems in a new iNav build is that you start with much less pitch and roll control  in Acro and Angle compared to Manual. I have been caught a few times with insufficient pitch control to get over trees while testing stabilised modes.

My FF ends up at 50 to 100 depending on the model. D and I terms are less important for fixed wing. Mine seem to end up around D=7 and I=10 but I'll do some further PIFF testing to confirm.

Autotune attempts to do these adjustments for you, but doesn't always get it right. I prefer to set them in the field using the  iNAV OSD Menu. Access the OSD Menu by using the Enter OSD Menu Stick Command. You can make all the adjustments using your transmitter sticks.

Check List before your first flight

On the bench and hooked up to your computer

1. iNav Configurator Receiver screen - Ail, Ele, Thr and Rud values must increase when you move the transmitter sticks up and to the right. This means the stabilisation will work in the correct direction. If one channel value doesn't increase, reverse the weight in your transmitter mixing.

2. Check that values range from 1000 to 2000 when you give full movement to the sticks. Adjust end points in your transmitter mixing if the range is out. I have to use -97 to +97 on my Taranis.

3. Check control surface movement using the transmitter sticks. If a servo is moving in the wrong direction go to the Servo screen in iNav Configurator and click Reverse for that servo.

4. Check that your Modes switches are working as expected and have no modes selected with all switches UP. With nothing selected the plane will be in ACRO Mode (also called Rate Mode, but will show in the OSD as AIR)

5. Check that the GPS is working and acquires more than 6 satellites. You will not be able to arm the board otherwise. Motor will not be active until the board is armed.

If all the above checks out you will be good to go. Time to be brave and throw that plane in the air.

Start in Manual Mode and fly up to a safe height, switch Manual off when you're flying calmly to see how ACRO mode performs. Be prepared to switch back to Manual if something unexpected happens.

Check other modes as your confidence builds.

More tips coming as I find them

Wednesday, 26 June 2019

Sky Hawk V2 Twin Fin Tail

I'm not convinced about the value of V and A tail configurations. They may serve practical purposes but seem to reduce yaw stability, and even pitch stability in turbulent wind.

So to try and improve the performance of the Sky Hawk I changed to a twin fin configuration.

Once I sorted out a twitchy elevator servo the results were very good.

Twin fins dimensions
150mm high
200mm long
50mm top

The forward extensions add strength and may help to organise the flow across the horizontal stabiliser.

Horizontal stabiliser is made from the old A-Tail halves, just cut off and glued together flat, with 20mm x 6mm depron added to the leading edge for extra area.

The wing foam flexes a bit around the boom mounts (shown by the icy pole sticks) so I may add some stiffening there

Flights with the new twin tail mod

Sunday, 23 June 2019

Sky Hawk V2 Mods

This excellent 960mm wingspan A-Tail can be set up as a twin motor or a single pusher.

I really like it's size and adaptability, small enough for easy handling, but has heaps of internal space for big batteries and flight control boards. Very similar size and performance to the Talon GT

However there are a few things that can be improved.
It's a bit lacking in yaw stability, which basically means it wiggles in any wind, mainly due to the A-Tail being too small. I have added more tail area using 6mm depron which has reduced the wiggle.

The battery bay cover is flat, meaning thicker batteries will not fit. I'm using a 3000 4S which just fits, but a domed cover would allow room for Li-Ion bundles.

For the moment, to create more battery space I have cut off the nose tab and made a tape hinge for the cover

The twin motor set up is very cool and makes for a very fast plane with a sweet twin motor sound, but it's less efficient than a single pusher setup. I changed to a single 2212 980kV SunnySky motor with a 9 x 6" prop running on 3000mAH 4S. It cruises at under 4A and has heaps of extra power for fast fun. Suprisingly the weight dropped by 10g changing from twins on a 2200mAH 3S to single pusher on a 3000 mAH 4S.

I have also sliced off the boxy FPV camera mount under the nose for less drag and to reduce grass and mud entering the nose.

Flying weight - 700g without FPV and FCB
850g with all the gear.

Banggood - Sky Hawk V2 PNP / KIT 

Single motor maiden

I'm adding a Matek F411 Wing flight control board running iNav 2.1 (June 2019) with a Runcam Eagle camera and Eachine 5.8GHz 200mW VTx.

Strange behavior and crash video

Monday, 3 June 2019

Smeg Head 1060mm Canard Pusher

This cruising FPV canard pusher is inspired by the Experimental Airlines APD

The original APD uses elevon mixing and a fixed canard, but I wanted to test ailerons and a separate elevator with a central fin.

Here is the Canard Center of Gravity calculator I used to get the balance right (after the maiden)

Maiden flight video

Build overview, mods and follow follow up flight

Carboard Box version

Tuesday, 28 May 2019

RSSI for iNav - X8R L9R XM+

RSSI (Received Signal Strength Indication) is a measure of the RC signal strength between the RC transmitter and model.

Having RSSI as one of the OSD (On Screen Display) items in your FPV feed means you can see the signal strength as you are flying.

According to this excellent RSSI setup video by Droneracer101 there are 5 different ways to configure your receiver, transmitter and flight control board to enable RSSI for your OSD. He is demonstrating with Betaflight but the same setups work for iNav.

This post is just my interpretation of Droneracer101's instructions that relate to my three types of SBUS receivers.

1. X8R, X6R and X4RSB Telemetry receivers
The X series receivers transmit RSSI to your transmitter by default. You can use this value as an Input for a spare channel, which is transmitted back to the receiver / FCB.

On your Taranis

In the INPUTS page create a new input

I chose I-01 and renamed it I-RSI  but it can be any input.

Change Source to RSSI
Change Scale to 100dB

In the Mixer page create a new mix for a spare channel (eg. Ch 11 but can be any spare channel)

Change Source to I-RSI (I-01)
Change Weight to 200
Change Offset to -100

This adjusts the RSSI value to a meaningful number in the OSD

Using iNav configurator

Configuration page - Turn Analogue RSSI Off

Receiver page - change the RSSI channel to Ch11

OSD page - enable RSSI and position it where you want on the screen

2. XM+ SBUS receiver
Digital RSSI on SBUS Ch 8 or Ch 16 from receiver to flight control board.
Requires the specific firmware upgrade for the XM+ receiver.

XM+ RSSI firmware upgrade and OSD setup video

Once you have installed the RSSI firmware, follow the iNav Configurator instructions above but choose Ch 8 or Ch 16 depending on your firmware choice.

Ch 8 or Ch 16 must be spare in your Taranis.

3. L9R long range non-telemetry receiver. Analogue RSSI
Analogue RSSI via direct connection. This will only be possible if the FCB supports Analogue RSSI by providing a solder pad or pin, and the receiver provides an Analogue RSSI pin.

Matek F405 Wing and F722 Wing boards support Analogue RSSI. F411 Wing board requires MATEKF411_RSSI firmware to allow RSSI on the STI pin (Thanks for the update Samantha)

Connect the RSSI pin on the L9R receiver to the RSSI pin on the FCB. Only the signal wire is needed.

Configuration page - Turn Analogue RSSI On

Trouble shooting
If you are having problems getting the OSD information to show up in your FPV feed the issue may be your camera, TV standard choice or ground wire connection. 

Try swapping to a different camera. Some FPV cameras will not play nicely with iNav OSD and flight control boards.

Make sure you are consistent with your PAL or NTSC choices for camera, video transmitter and iNav OSD.

Make sure your camera and video transmitter share a ground connection.

Sunday, 26 May 2019

Cardboard Canard Pusher

This canard pusher is made from the Sonic Modell Skyhunter Racing cardboard box.

Based on Ed's Ansley Peace Drone with a few mods.

I changed to a central vertical fin, and added a canard elevator rather than just elevons.

Here is a rough sketch plan. The design can be scaled to whatever box or materials you have.

CG is roughly half way between the canard and main wing.

Build and flight video

Some sloping in this video

Here's my original depron Ansley Peace Drone

Saturday, 2 March 2019

iNav Basics - Trim and Modes


IMPORTANT: Do not use any mixing, reduced rates, expo or trims in your transmitter.

The Flight Control Board handles all the mixing for you, including elevon mixing for wings and V-Tail mixing. All you need to do is program in 100% weight for each stick on Channels 1 to 4, and assign Mode switches to other channels.

My latest setup on the Taranis Q X7 (27th April 2019)

Ch1 100 Aileron
Ch2 100 Elevator
Ch3 100 Throttle
Ch4 100 Rudder
Ch5 Switch F (Arming) 
Ch6 Switch B (Angle and Launch Assist)
Ch7 Switch C (Alt Hold with Nav Cruise, and Alt Hold with Position Hold)
Ch8 Switch D (Manual and Return to Home)
Ch9 Switch A (Auto Trim and Auto Tune)


IMPORTANT: Do not trim the plane using the transmitter trims

There are three types of trimming required for consistant behaviour across all modes

1. Trimming the control surfaces for level flight in Manual mode

First you must fly the plane in Manual mode and adjust the push rods (not the transmitter trims) for "hands off" level flight. iNav will ignore the transmitter trims in all Modes apart from Manual.

If your pushrods are not adjustable you can use the new iNav Auto Trim mode. See below for details.

2. Trimming the board alignment for level flight in Angle and Horizon modes

One of the most common problems with a new iNav installation is that the plane will lose altitude in Angle and Horizon modes. Don't be tempted to use the transmitter elevator trims to fix this behaviour.

Level flight in Angle or Horizon depends on the mounting alignment of the board. Most planes need some positive angle of attack or "nose up" to maintain altitude.

So it is usually necessary to add about +3 to +5 Pitch Degrees in the Configuration screen for the plane to maintain altitude in Angle / Horizon Mode. This depends on the plane and how you mount the board relative to the wing chord.

Angle and Horizon mode trim depends on board alignment (gyros and accelerometers)
Manual mode trim depends on control surfaces (Pushrods and servo angles)
GPS modes depend on GPS satellite information.

So you can see that switching out of a GPS mode may give nasty surprises if the control surfaces and board alignment are not quite right.

3. Auto Trim and Tune Modes

Auto Trim (for Manual Mode)
This mode attempts to adjust the servo mid points for level flight in Manual mode. Good for fine tuning trims once the pushrods have been adjusted correctly, or for fixed pushrods.

Pick a calm day, and while flying level in Manual mode, switch Auto Trim on.
The servo mid points over the first 2 seconds will be recorded.
If you are happy that the plane stayed level during those 2 seconds leave Auto Trim On and land the plane, disarm the board and the new trims will be saved.

Auto Tune (for Stabilised Modes)
This is another new mode that attempts to tune your PIFF values (Proportional, Integral and Feed Forward) for smooth stabilised flight with good control from stick inputs. iNav will learn how much control you need after analysing the reaction of the plane to your stick inputs.

Note: FF is the fixed wing replacement for D (Derivative). But it's still labelled as D in the iNav configurator PID screen.

Pick a calm day, launch and fly with no modes selected. The plane will be in Acro Mode (also called AIR) if no other modes are selected. Activate Auto Tune once you are flying comfortably.

Fly around giving full aileron stick movements left and right for at least 30sec, then repeat for the elevator, then the rudder. Initially the response will be very mild, but movement will increase as the test goes on.

Keep repeating the movements for a few minutes until the change in behaviour stabilises. Auto Tune records the new PIFF values every 5 seconds.

Turn Auto Tune OFF in the air, then land, let the plane sit for a few seconds then disarm.
The new PIFFs have not yet been permanently saved to the board. You need to Save with Stick Commands, or connect a Laptop and save using iNav Configurator.

Stick Commands
This is the simplest way to save the new PIFFs
While the board is disarmed, push the transmitter sticks full down and away from centre. The new settings will be saved.

The new PIFFs can be checked by opening the full OSD menu.

With the board disarmed, push the Throttle stick to the center, Rudder stick full left, and Elevator stick full up.

Note: Some users have trouble bringing up the OSD successfully. There are a few tricks to this.

Throttle, Rudder, Aileron and Elevator outputs must be active with full range and the board disarmed.

That means you can't have Throttle Cut or Channel Override activated (different to disarm), you must have a Rudder channel setup (even for flying wings) and you must ensure your stick movements give the full range output (1000 to 2000) in the iNav configurator Receiver page.

Full list of stick Commands. Arm and Disarm are deactivated if you use switch arming.

There are three types of Modes available in iNav.

Full control modes

Manual or Passthrough Mode
Normal flying with no stabilisation, only the Expo value in iNav is used. If something is going wrong with the FCB or GPS switch back to this mode to take control.

Acro or Air Mode
Slightly stabilised, holds the current orientation rather than self levelling, full control. Always active when no other mode is selected

Stabilisation modes 
These are Gyro and Accelerometer driven modes that rely on the board being level when the plane is in level flight attitude. Most planes fly level with the nose a few degrees up, so the board may need to be tilted down at the front, either in the mounting position or in iNav setup board alignment.

The Pitch Degrees required varies with different wings and different flying speeds. I usually start with +5ยบ and adjust from there after test flights.

Angle mode
Fully stabilised, bank and pitch angles limited, will return to level. Can't do loops and rolls in this mode.

Horizon made
Starts off like Angle mode but allows greater control as the sticks are moved further.

Launch Assist Mode
This is a magic mode. Select Launch Assist, arm the board, advance the throttle to a good launch percentage (the motor will not spin up yet) throw the plane and the motor will spin up 0.5 sec after the throw acceleration is detected. The plane will climb for 5 sec then switch into any other mode you have selected, or until you move the sticks. I have used Launch Assist and RTL combined, so I can can launch and let the plane circle above without picking up the transmitter. A big crowd pleaser.

It's important to get the switch sequence right for Launch Assist to work.

GPS modes
These are GPS controlled modes, and they can be combined with the Stabilisation modes.

Altitude Hold
Does what it says, holds the flight path at the Altitude when selected. Very useful for level and stable flight paths.

Position Hold
The plane will circle around the point where the mode is selected, at the radius selected in iNav setup. Relies on a properly aligned FCB for altitude. Best to combine with Altitude Hold mode for a very useful Loiter mode.

Heading Hold
Uses rudder to hold the flight path to the heading when selected. Combine with Altitude hold for fixed heading and altitude flight path.

Return to Launch (RTL)
This is what it's all about. Enter this mode and the plane will fly back to where it was armed, at whatever altitude and throttle percentage you have setup in iNav, then circle overhead at the iNav setup altitude and radius (or even land automatically if you're game)

Failsafe RTL
For me this is the main reason for using iNav. Failsafe can be setup to go into RTL mode, meaning that if you lose radio contact with your plane it will fly back home.
On FrSKY X series receivers I set the failsafe to No Pulses, then in iNav - Failsafe RTL - Don't Land.

Here is the iNav Fixed Wing guide which will answer most questions - iNav FW Wiki
Here are all my iNav related videos on YouTube - iNav Playlist