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Feb 21, 2019, 08:51 PM
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Build Log

LED Afterburner(s)

I have never really worried much about not having any 'Afterburners' on jets that the full scale version does have it, but I had bought a few of the various Afterburner 'kits' that have been around over the years. eg RC Lander, done as a ring of LEDs to go on the very exhaust of the jet.
These had numerous fitting issues and downsides so I never actually used any.....

When RCgeek started selling some, and with the 'new' idea of using LEDs on the actual EDF motor, it began to seem a more useful idea.
But the cost to get those to Australia is a LOT!! Too much for even one jet, let alone a bunch of them!
So I decided to make up my own version.

4stripes from RCG also 'reminded' me of the idea to make my own, based on that 'on the motor' idea, and it raised my enthusiasm to actually do something!

A single 10W LED makes it easier to do than using many smaller LED's.....

If you only switch the LED On... and Off.... then the driving circuit is extremely simple.
If you want it to Flicker at the On/Off transition region then that gets notably more complex compared to just On/Off, but is still not that hard to implement.

Then there is a third option/possibility, where you have 'unlimited' control of the colours and timings - though what variations and true needs of these possibilities are there? This would be done with the use of a microprocesser unit, such as an Aduino Nano etc. Very small and very cheap.

I decided that my criteria is to at least have 'Flickering'.
So HOW to achieve that?
There seems to be two main ways for the moment. A 'local' on board controller. Or via using another TX channel and doing it at the TX itself.

On the TX you could just form a process Mixed from the Throttle Channel, to vary the On/Off behaviour of the on board RC Switch you would have to control the LED in the aircraft. Thus any form of flickering etc you could want is easy enough to create.

For an on board controller, you need some circuitry designed to form this desired flickering pattern. One simple way is to use an Arduino, though seems like an overkill. But it is small and would do it all fine - with infinitely more capability than you would ever even need or use.
Another circuit would be to build some system that checks the throttle command value and then uses a timer, or more, to generate pulsing/flickering..... hmmm, the effort to design and build this is much more effort than using a SIMPLE and cheap, overkill, Arduino!!
An Arduino also has a 'standard' ability to read PWM signals too - so in all ways it is all ready set and tailored to do everything and anything this task could need!

Using an Arduino means it is all self contained - no need for TX setup/programming at all..... so really, this is the most universally workable idea!

Another Arduino benefit is that is could be used to do other tasks too... many other tasks! Like.... ummm... who knows....
It can also drive an RGB 10W LED version, which then means you can ue any colours you want... in any sequences, patterns, reasons, you want.

An Arduino cannot drive a 10W LED directly itself..... the LED needs too much Current. So a little bit of extra circuitry is needed to take the Arduino signals and switch a more powerful Transistor or FET to drive the LED. Just one channel to drive a plain 'yellow' LED, or three channels to drive and RGB LED version.

This whole assembly (of all required electronics) would be done as a 'control unit' and all that needs is the input lead (12v), and the output lead that runs to the LED. You would either heatshrink it all, otherwise put it into a small case/box.

An Arduino Nano costs approx AUD$3.80 from China. And the rest of the few components about 30c....
The 10W LED in Yellow or RGB, is approx AUD$4.00 (You can get 10W, 20W, 30W, 50W, 100W !!)
So in total all the parts are well under $10.

Hmmm, you also need a roll of Aluminium Tape... $10 approx. This is to line the exhaust ducting of the jet, so that lighting reflects all the way down to the rear end.
But that roll/amount would do a LOT of jets! So in total the cost is still sub $10.

I have pondered over the way I would want the Afterburner to work/look......

I wondered if I want... need.... any colors. Maybe at various AB stages. I sort of thought that maybe you see some 'blue', or orangey/blue, at some stages.
So I looked at a heap of jets with AB's in use, or coming into use..... overall it seems that really they most often are just 'nothing' there, and then a pretty well instant switch to yellow/WHITE. Not Orange... not Yellow... but more White than Yellow.....

So I did buy both the Yellow LED version and the RGB version in case. To get a more White biased Yellow (or any other shades/colors) you would need to use RGB.....

Plus if you are more towards 'White' then that uses more light to achieve that, so the output is even brighter - than say for just yellow.

Using the RGB version also means you can CHANGE it simply just via the Arduino programming to whatever you want in the future also.

Another thing I was pondering was CONTRAST.
White/Yellow is less of a contrast to the outside of the aircraft than, say, Orange would be... or even plain Yellow.....
So you have this trade-off issue of better contrast versus true colors of a full scale jet AB.

Then another pondering....
With the Arduino being massively more capable, you can even take another TX/RX Channel dedicated to real-time color changing. In various ways, but for eg you could use a Pot that runs the LED output across a colour range. eg from White, through yellow to orange, to red - and via all the shades between those.
Or use an OpenTX LUA script that gives you a complete colour control panel! To dial in ANY colour... RGB... set you want!
I guess this is something it should include in the Arduino coding done, as it is pretty easy and may as well be ready to utilise it... or just not use it if you don't want to.

So next is on to the prototyping.............
Last edited by PeterVRC; Mar 06, 2019 at 06:01 PM.
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Feb 21, 2019, 09:34 PM
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Full scale jets

So off I went to check more images and videos of various jet types, to see what AB colors they have....
Hmmm, mainly towards a darker orange.... and I could not find any of the ones I had seen in more of a white/yellow....

Interesting was the F-4 Phantoms having anything from orange, darker orange, to a BLUISH color!
This video below, of a group of F-4's taking off, has a number of variations across them.

So what this means is the best is to make it PROGRAMMABLE, with the RGB LED version, Then you can make any jet have its 'right' colors, or even alter them at times etc.

8 x F-4 AUP Phantom II taking off with full afterburner (3 min 58 sec)
Mar 18, 2019, 03:47 AM
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Design Choice

It took a while for some of the possible useful parts to come from China.....

The first useful item is a Constant Current LED Driver module, which you can set to feed the exact Current (MilliAmps) to optimise the LED output, but it also makes it a constant no matter what charge level the Voltage source, battery, is at.
It is actually a DC-DC Step Down device, but the IC used supports Constant Current output also. So this means it can take any Input Voltage from 5v to 35v, and output a Constant Current - which is done by varying the output VOLTAGE precisely to achieve that resultant.
It is just perfect for this use because it means you can use any Lipo source up to 8S, plus the unit also has a PWM Control Input which can alter the output level. This input is sort of an On/Off input that a PWM signal means it will turn on and off rapidly, at the PWM High/Low ratio. A LOW input turns it ON, and a High turns it Off. So if a PWM signal is 70% high, and 30% Low periods, the LED will be run at 30% brightness.

This unit is ALMOST all you need... but unfortunately not quite.....

It is not actually needed as a DIMMER at all..... but just as a Constant Current source, to assure constant full brightness for any input Voltage.... plus the ability to turn the LED On and Off,, under a Digital Signal Level control (The PWM input control).
For this use it will be OFF..... for Throttle levels under, say, 70%. Then ON.... for Throttle levels 80% or higher.
And for 70% to 80% Throttle range it will FLICKER On and Off erratically - plus the 'erratic flicker' will increase in ON time as it rises from 70% to 80%, where it then becomes that solid ON.

So this needs a way to form those control inputs to the unit.....
An RC "PWM signal" is NOT the same form of PWM !!! RC is more of a "PPM on PWM" sort of signal, and is not just a 'normal' PWM signal then.
But we want to... need to.. use the RC Throttle PWM signal to form the real PWM signal. To read the Throttle value to do the LED Driver module On/Off controls.

This could be done with circuitry made up, but the multiple parts and their costs - even though low - cannot beat an Arduino Nano, which is only $5
This LED Driver Module is $1.75
An Arduino can read RC PWM.... and coding, programming it, can form whatever 'normal' PWM output you need to control the LED Driver module..
An Arduino can also be reprogrammed to any changes you might ever think to want/need.... changes in anything.... On or Off points, Flicker manner etc. It is also very small, and about the same footprint as the LED Driver Module so it can sit back to back with that (I think).
So it is just the best choice/option to use!

I already have those, and other Arduinos, so I began the coding the other night - but found some simple things I didn't know how to achieve and need to read up a bit on those. But all things are simple and quick enough to find, read, learn anyway. I should get it working within a few days....
Plus I need to test if the Arduino Nano and LED Driver Module being NEAR each other will bother the Arduino (interference due to the Switching Circuit of the LED Driver). At worst they would need to be kept as separate items, which is no worse than if you have a unit that needs to run from an SBEC anyway.

Mar 18, 2019, 03:57 AM
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Thread OP
Hmmm, I just thought of a better idea....
In the Arduino programming, it could be made to have read TWO RC PWM inputs.
The Throttle, and also another dedicated Channel just for Afterburner Control.
The reason for this is that you could control it as per I laid out above..... but have multiple programmed sequences, and use the 'Control Channel' to choose alternate operations.
There are even a lot of other uses that reading another Channel, or even more, could have it do.

And if there is no Control Channel connected, it defaults to one of the sequences....

Which just made me think of the recent years of Freewing jets that include a Control Unit.... which is probably just an Atmega processor set up to do all the tasks that each plane has it do...? I have not checked if it is Atmega (as per Arduino use) or some other dedicated LSI chip. But that concept is the same thing as this Afterburner 'processor'. Create a unit that can be 'made' to control things you want/need....
Mar 19, 2019, 06:00 AM
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Version 1

I joined the Arduino Nano and 350mA Constant Current Driver back to back - the Nano is just a bit longer than the driver board, but also a bit narrower.
There is no interference affecting the Nano operation.
I have not decided how to Enclose it yet..... box? Acetate sheet box? 3D Printed light weight box? Thin wall heatshrink?

I did discover a 'problem'. The Nano needs 7v to 12v (technically up to 20v even) to run it, whilst the LED Driver can be 5v to 35v - thus the Nano sets the Voltage to choose.
That is a range of value in Lipo cells from 2S to 3S .
To make it 'universal' up to 8S you would need an SBEC or cheap regulator - but with that 7v to 12v range of output. You can modify any SBEC to do that... or notably cheaper is just to buy the common DC-DC convertors from eBay.
BUT this method means another small module = larger total volume/size.

OR...... you could just use 3S of the balance connector, to any battery type....
You can modify a 6S JST-XH connector to take 3,4,5,6S with still one KEY at one end, so that it clips on securely to any of those 3,4,5,6S balance leads still.
The Current used by the AB System is very low, so any cell imbalance from doing it that way will be insignificant.
I will most likely use this method.

For Version1 I just whipped up a system that a RISING Throttle signal passing through 2000uS will trigger a rapidly increasing frequency flickering sequence which then turns to solid LED ON. But coming down through that it just changes to LED OFF instantly.
There are various ways to make this real-time programmable - to change trigger points etc. Either via attached Trim Pot(s), or via RC command - or include both. eg a Trim Pot you can alter to set where the trigger/flash point begins.
For the moment the plain "Flicker-ON, instant-Off" seems fine enough.... though I guess I should just add the on board Trim Pot control mode also really. Just in case I want to 'tune' it.
Without either type, you can still plug in a PC (Notebook etc) and alter the programming that way.

My 3D Printer is 'sick' and awaiting some parts to fix/improve it, so I can't make the 3D Printed motor mount for the LED yet!!
Though even that needs to be made "EDF Specific" to suit the motor/EDF type it will be attached to.
I am not sure how Universal I can make that be.

It is also possible that making a LED mount to the Ducting WALL, right after the EDF, could still light it all up just as well anyway.... so I will try that idea too. The aluminium tape that the Ducting will be lined with could very well 'scatter' the light enough/plenty and thus still even it all out fine anyway.

AfterBurner LED unit (0 min 56 sec)

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