Tuesday, 24 October 2017

iNav fixed wing tips

October 2017 - Betaflight is the most recent firmware for flight control boards (FCBs) and iNav is the GPS enabled
re-write of Betaflight which also caters for fixed wing models.

All the setup is done using the Chrome App called iNav Configurator. Works on PC and Mac as long as you can locate the correct drivers for the board you have. All the information on iNav is kept in the iNav Wiki on GitHub

I'm quite new to all this auto pilot stuff and there is a steep learning curve, so I thought I could pass on what I have learned so far.

So far I have experience with the Paris Sirius AIR3 F3 board with GPS from Multiwiicopter

and the Omnibus F4 V1 board and Ublox Neo M8N GPS module from Banggood.

The value of the AIR3 board is that it comes mounted in a gel damped housing with all the connectors and GPS sensor, and it's pre-loaded with the latest stable iNav firmware. Most of the tricky stuff is already done for you.

The AIR3 is an F3 board and doesn't have a built in OSD, but an addon OSD is available. The AIR3 OSD is configured using the MWOSD Chrome App, and partially by using your transmitter sticks.

If you're handy with a soldering iron and want to do it all yourself, you can follow Matt Ogbourne's video series on the Omnibus board setup. You will have to do all the soldering, firmware flashing and setup yourself. The Omnibus F4 does have a built-in OSD, which is configured in the iNav Configurator.

About Flight Control Boards
The connections to FCBs are a little more tricky than normal ESC/receiver/servo connections because FCBs are more sensitive to incorrect or fluctuating voltage supply. With voltage spikes, FCBs can shut down, brown out or reboot causing total loss of control of the model.

It is highly recommended that the board and servos are powered by an accurate and stable 5.0V BEC like the AIR3 iNav BEC. You need to make up a power distribution cable so the BEC can plug into the board, and power the servos separately. As the 5.0V is being supplied to the FCB by the BEC you must disconnect the 5V line (red wire) from the ESC. Not a good idea to have two power sources for the FCB. Then all the signal wires from the servos and ESC connect to the board. The ground wires can either connect to the BEC or the board.

Another recommended precaution is to plug a voltage smoothing capacitor into your FCB, like this 3300uF 25V from MultiWiiCopter. The capacitor connects to any spare output pin-set across the power and ground pins, and absorbs any voltage fluctuations. Can also be plugged into receivers for added safety.

If you want to live dangerously you can just plug the servos and ESC straight into the board. like you would with a receiver, but you are only one voltage spike away from a crash.

Transmitter setup
You do not use any mixing, rates, expo or trims in your transmitter.
Just program in 100% for each stick and whatever Mode switches you need.

My setup on the Taranis is:
Ch1 100 Aileron
Ch2 100 Elevator
Ch3 100 Throttle
Ch4 100 Rudder
Ch5 Switch E (Arming)
Ch6 Switch A (Air, Horizon and Angle modes)
Ch7 Switch D (Loiter and Return to Home modes)
Ch8 Switch C (Pass through and Launch assist modes)

iNav tips
There are three types of Modes available in iNav.

Full control modes

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.

Air Mode
Slightly stabilised, 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. Actually what we need is the board mounted level with the airfoil chord line a few degrees up. It varies with different wings and different flying speeds so to get this right you need to fly the plane and make appropriate adjustments to the board alignment in the field, without using Transmitter trims. See Plane Trimming Tips below.

Angle mode
Fully stabilised, bank and pitch angles limited. 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 when combined with Angle or Horizon modes 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.

Important plane trimming tips
The correct way to trim your plane is to adjust the push rods and servo arms mechanically so it flies level and the control surface throws are OK with no trims or rates needed in the transmitter. Then you trim the FCB alignment, either physically or in iNav (using a laptop in the field), so the plane flies level in Angle or Horizon modes.
If you don't do this the plane will behave differently depending on which mode you're in. It might, for example, go nose up in Passthrough mode and nose down in Horizon mode. Of course GPS modes can mask any trim issues.

Here are all my iNav related videos on YouTube - iNav Playlist

Thursday, 10 August 2017

The Boxler - Packing box plane

For years I have wanted to make a plane from an RC plane polystyrene packing box.

In the recent Hobby King sale I bought a Bix3, so here was my opportunity to give this project a go.

For speed and simplicity I decided to make a simple 3 channel motor glider with no ailerons. I covered the foam with packing tape and used fibre reinforced tape like spars on the wing and fuselage. I also decided to try a flat wing with no airfoil and dihedral tips.

This video shows the build from start to finish.

Here's the maiden flight which went better than expected.

I then made a hot-wire cut Clark Z airfoil wing to compare to the flat wing.

The airfoil wing had a much better glide slope and smoother flight performance.

Here are some mad wing tests using the flat and Clark Z wings.

Dimensions in cm

Length 100cm
Flying weight 590g
with 1300 3S Lipo
Motor 2822 1450kv
7" x 4" prop

Thursday, 20 July 2017

What FPV cameras do I use?

I'm no FPV expert and actually prefer line of sight flying. However I do dabble with fixed wing FPV occasionally and really enjoy having the plane in the video view. This could be called Third Person View maybe. I have very little interest in FPV multirotors.
Here is a playlist of all my FPV reviews - Youtube link

FPV Cameras
There are so many options these days with Foxeer and Runcam competing almost weekly with new dedicated FPV cameras, and most action cams offering FPV or TV Out as well.

It's important to note that our analogue video transmitters only send standard definition video. The picture quality is not great compared to even the most basic Action cam recording. High definition video transmitters are currently too expensive, too bulky and too slow, so they are not often used for FPV.

You can use dedicated FPV cameras or Action cams for FPV, but it's probably safer to use a dedicated FPV camera because Action cams can shut down or freeze with low battery or insufficient storage space. Dedicated FPV cameras tend to have much less delay or latency in the video feed than action cams as well, which is important for control at high speed. FPV cameras are usually 4:3 aspect ratio and Action cams are 16:9.

Dedicated FPV cameras
These are really just fancy security cameras, mostly with CCD sensors but a few with CMOS sensors. They usually have screw mounted lenses ranging through 2.8mm, 2.5mm and 2.1mm. I prefer the widest view of a 2.1mm lens and these can be purchased from places like Banggood for a few dollars.
Either the sensor or the lens will have an Infra Red filter fitted. In most cases the IR filter is on the sensor so you would buy a lens without the IR filter. Most are 4:3 aspect ratio and standard definition. 16:9 aspect ratio cameras are becoming available. If the option is available it is a good idea to turn on High Dynamic Range or DHDR in the camera setup to give the best video feed in difficult lighting conditions.

Surveilzone, Foxeer and Runcam HS1177
This is the first FPC cam I bought, mainly for it's small low drag casing. It turned out to be the most commonly used FPV camera in the RC community. It has a 4:3 600TVL CCD sensor which handles light and dark areas better than the cheap CMOS cameras.

Here is a review of the Runcam PZ0420M and Foxeer HS1177

Runcam OWL plus 4:3 - Gearbest link
In the above review I also look at the Runcam OWL plus with it's enhanced low light sensitivity.
This camera is a night flight specialist.

Runcam EAGLE 16:9 CMOS - Runcam link
The Eagle is the first of a new breed of FPV cam using a CMOS sensor with enhanced global high dynamic range. That means that the video image is processed to ensure there are no blown out skies or dark foreground. The effect is amazing and makes FPV flying a wonderful experience. With cheaper cameras on cloudy days it's almost impossible to fly because all you see in the goggles is black ground or white sky. The Eagle brings back all the detail and comes in a wide screen 16:9 aspect ratio version. Most other cameras are 4:3 aspect ratio. This is quite an expensive FPV camera at about A$80 and the default sharpening settings are too high, giving jaggy and shimmering edges, but after adjustment this is a superior FPV cam. This is my favourite FPV camera for old school cruising because it fills the screen of my 16:9 goggles with an unstretched image. However it doesn't have flight battery voltage OSD.

Foxeer MONSTER (Version 1) 16:9 - Tomtop link
This is a cheaper 16:9 aspect ratio camera with 1200TVL CMOS sensor and 2.8mm lens. It's a great camera in sunny conditions with that lovely screen filling 16:9 view.
There is a second version now available with on screen display and WDR added.

Foxeer New Arrow - Tomtop link
Foxeer Arrow 3 - Banggood link
Runcam Swift 2 - Runcam link

These are the latest high quality 4:3 aspect ratio FPV cameras and are currently the most commonly used in the RC community. They have evolved from the early HS1177 to offer excellent HDR and On Screen Display of flight battery voltage, pilot name and flight time. This is a fantastic development meaning you don't need a separate system for OSD to keep track of your battery voltage. However you do need to connect an extra wire from the battery + lead to the camera.

See my FPV playlist for reviews.
Any of these three are my favourites for fast flying wings, because of the voltage OSD and easier to view 4:3 aspect ratio at high speed.

Runcam Swift mini - Banggood link
This is a smaller version of the Runcam Swift without the OSD, designed for mounting in smaller spaces.

All of the above cameras can be powered by 2S to 4S batteries or 5 to 17 volts. Some other cameras can only take 5V. You must read the specs to determine what your camera requires.

Coming next - FPV transmitters, receivers and antennas

Tuesday, 18 July 2017

What cameras do I use?

This would be the most frequently asked question on my YouTube channel, so it merits a more detailed explanation.

For onboard footage I use a Mobius C2 purchased from Ebay seller eletoponline365  (Recommended seller on the RCGroups Mobius thread)
It's fairly basic with no image stabilisation and maximum res of 1080 30P but the image quality is very pleasing and the audio is the best of all flat form action cams (that I have tested). The Runcam 2 and Foxeer Legend 1 may be slightly sharper and offer higher res, but the results from the Mobius just look and sound better in my opinion. I also use this Mobius for audio recording when I'm flying FPV and need to narrate. I set up Mode 2 to be WAV Audio only recording. Initially I used the smaller 808 #16 key chain camera which did a good job but was limited to 720 resolution.

For hatcam footage and narration while flying I use a Mobius A (narrower field of view lens) This gives a closer view of the plane in the air without being too magnified. I have modded the microphone to be external and enclosed in a very effective wind sock. This means I can narrate a flight in strong wind and still have decent voice quality.

For a tripod mounted camera out in the field and "talking to camera" reviews I use an SJCAM M20 for it's nice contrast and sharp lens. I use it on 1080 30P which gives a slightly narrower field of view than the full fisheye. It also renders skin tones smoothly too which is a bonus for my ageing weather beaten face.

For close-up cut away shots I use a Canon S100 compact camera. It does a decent job but struggles with auto focus accuracy occasionally.

Audio recording for the indoor reviews is on a Zoom H1 audio recorder with Clippy lapel microphone from Micbooster in UK. That usually works well but has started letting me down with fuzzy recordings and scratchy connection interference lately. I'm now trying a Rode smartLav+ mic with my iPhone as the recorder and that sounds promising. Occasionally I will clean up the sound using the free Audacity program.

For editing I use iMovie on a Retina display 27" iMac. That's all I need for my quick and dirty Youtube videos.

I have tested many GoPro style action cams, and there are some good and some not so good options. My first action cam was a  GoPro 2 which I loved at the time, then a GoPro 3+ Silver which was a waste of money with poor focus and green colour cast. The first "post GoPro" action cam I tried was the SJCAM M20, and that prompted me to throw the GoPro 3 in a drawer and stop using my Nikon D7000 DSLR for video.

I divide the Action cams into 3 categories:

The SJCAM SJ7 and ThiEYE T5e give the best video image quality with great sharpness and natural smooth colours and tones. But the audio on both of these cameras is not perfect, a bit muddy and ever so slightly out of sync with the picture.

The SJCAM M20, SJ5000 and SJ6 fit in this category with sharp video and bright colours. However they produce slightly posterised tones and compression artefacts in some situations. The Eken V8s also just makes it into this level with nice features but slightly less sharpness in the video.

These cameras are cheap and work fine but cheaper lenses and electronics compromise image quality more than I am happy with, like the Andoer AN5000, Hawkeye Firefly 7S and Tomtop 4K action cam.

Reviews on all of these cameras can be found in this Action Cam playlist 

Saturday, 18 March 2017

DIY Wing incidence meter

Here is my simple home made wing incidence meter. Used to determine the correct mounting angle for wings.

There is much debate about the correct angle of incidence required for efficient flight but a good starting point is to have the horizontal stabiliser and wing both at zero angle, then adjustments can be made after flight tests.

A4 sized plans - download and print for your own use.

Video explaining how to use the Newton Incidence meter
(You can buy a proper one made by Robart)

Sunday, 22 January 2017

Eachine VR D2 FPV goggles

Banggood sent these goggles to me for review. I needed to add 2 x plus 4 close-up glasses before I could focus on the screen. I really like the diversity receiver with antennas supplies. One clover leaf and one patch antenna. And I love the built in DVR.

BANGGOOD purchase link

Here are the recorded video sizes with examples, and the review video with some flight footage.
(Images are not exact scaled sizes - limited by Blogger image display options)

4:3 camera - VGA recording 640 x 480 (4:3)

4:3 camera - D1 recording 720 x 480 (3:2)

4:3 camera - HD recording 1280 x 720 (16:9)

Mobius 16:9 camera - VGA recording 640 x 480 (4:3)

Mobius 16:9 camera - D1 recording 720 x 480 (3:2)

Mobius 16:9 camera - HD recording 1280 x 720 (16:9)

Review video on YouTube