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New Project: Arduino based AOA solution (G3X)

Brantel

Brantel

Well Known Member
I am thinking of working on an Arduino based AOA solution as a side project.

My plan is to make a low cost AOA computer out of an Arduino and a small list of components.

Why? Well my plan to upgrade my panel includes a G3X based design and they do not currently support AOA. I have grown to love having a remote AOA display being driven by my current Dynon EFIS. Details on that project here. Also the off the shelf models are too dang expensive and I like to build projects and tinker so here we go....

This new AOA computer/display will be based on and very similar to the prior project only it will do it's own AOA calculating instead of relying on an EFIS to do it.

So far the rough BOM has these major components:

1ea Arduino UNO (This is what I have on hand. One of the smaller cheaper ones most likely will work after the prototype is developed.)
2ea Differential Pressure Sensors (I have ordered two ranges to experiment on what gives the best resolution. +-3psi and +-1psi 0Vmin/2.5v@0DP/5Vmax. This is what is readily available off the shelf)
1ea Dynon AOA pitot (I will tap into the Pitot/Static/AOA lines existing in my A/C)
1ea Array of LED's of choice
1ea Ambient Light Sensor for auto dimming
1ea small switching transistor for PWM dimming the LED array
1ea small project box

Design intent:

It is pretty simple. Take the two DP sensors, tie one pneumatic port of each of them together with some tubing/T and connect that to the static line of my A/C. Take the other port of sensor1 (AOA Pressure) and connect it to the AOA line off of my Dynon AOA Pitot. Take the other port of sensor2 (Pitot Pressure) to the pitot line off of my Dynon AOA Pitot.

Bring those variables into the Arduino via the analog ports.
Scale to the AD converter output to something human readable.
Divide the "AOA Pressure" variable by the "Pitot Pressure" variable and create a "Raw AOA" variable.

Develop some sort of calibration routine that scales the "Raw AOA" variable across 4 calibration points.

1. Zero lift
2. Best performance ~ 1.5 x stall
3. Best approach ~ 1.4 x stall
4. High angle warning ~ 1.15 x stall
Since the Raw AOA variable should be fairly linear, there is no need to go all the way to a stall, it can be calculated.

There will be two calibrations to account for flaps and no flaps. I plan to use the Arduino serial port to monitor the G3X's datastream for the flap position in order to not require an additional flap deployed switch.

Thinking of another glare shield mounted LED array display similar to the one I did before.

Planning the following LED configuration:

rwnebd.jpg


I will also provide a tone generator output that will provide progressive tones as one approaches #4 above.

There will be an ambient light sensor that will enable automatic dimming of the LED array using the PWM output of the Arduino to control a small switching transistor sinking the LED array current. I did this on my prior project and it works great.

This should be able to be built for less than $100 not counting the Dynon AOA Pitot. Several examples of how to build your own AOA probe are in the archives of this forum.
Anyone got any additional ideas or suggestions?

FYI, this project will be open source, not for profit, not commercially produced and for personal use/education only.
 
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Brantel said:
I am thinking of working on an Arduino based AOA solution as a side project.

My plan is to make a low cost AOA computer out of an Arduino and a small list of components.

Why? Well my plan to upgrade my panel includes a G3X based design and they do not currently support AOA. I have grown to love having a remote AOA display being driven by my current Dynon EFIS. Details on that project here. Also the off the shelf models are too dang expensive and I like to build projects and tinker so here we go....
Click to expand...

I'm in. I downloaded the Arduino development suite last night. It is pretty cool; I retired from a career of C programming and now get to use it to add features to "Sky Terrier" :D
 
Fun!

I've been messing with Arduino hardware for about a month now. Fun stuff! My day job is software development at a very high level of abstraction so I find it very refreshing to work in such a simple environment much closer to real hardware. I have an Arduino UNO sitting on my desk with some flashing lights, buttons, and a few sensors.

It's only a matter of time before some Arduino project finds it's way into my airplane. :D

Would love to help you develop this in the hope that I might learn something. My airplane has an AoA sport from before Advanced Flight Systems bought it. This configuration of pressure ports doesn't require any fancy pitot tube so, from that perspective, is cheaper. But, it does need 3 pressure sensors. See here.

Where are you sourcing your pressure sensors?

Send me a PM or email ([email protected]) if you want to collaborate and we'll work out a good method of sharing knowledge and communicating. I use GIT for work and have access to all kinds of online resources.

Great idea!
 
FYI because I failed to mention it in the original post, this project will be open source, not for profit, not commercially produced and for personal use/education only.
 
I'd be interested in getting invloved! I built something sort of similar once upon a time... It was a boost gauge for turbo cars, used a little SMD pressure sensor, a pic micro, a dc/dc power supply, and a 9 led SMD arc display and a 2 digit 7seg numeric readout.

I've also got a bunch of arduino stuff on hand and some pressure sensors leftover from the last project.
 
Brantel said:
FYI because I failed to mention it in the original post, this project will be open source, not for profit, not commercially produced and for personal use/education only.
Click to expand...

And for those of us who have no chance in the world of doing this on our own, will there be kits or at least schematics and instructions etc available?
 
Mike,

We will make it open source and post all the info you would need to build your own educational project right here.
 
I'm in and strongly recommend hosting source, schematics, etc. at github.com. Git is without question the most powerful collaborative software development tool I have seen in my professional career.

Oh yeah, I have also done quite a bit of tinkering with Arduino. Very cool stuff.
 
jbagley said:
But, it does need 3 pressure sensors.
Click to expand...

Pretty sure it only uses two DP sensors. One on the 2 wing ports and one for pitot/static.

I think we can get away with two with one side of em tied common to the static system. That way we can use the Dynon pitot or people can roll their own AOA probe or make their own wing ports.
 
If you guys want to think about drawing up some examples of DIY probes, I may be able to machine some up...

Thinking maybe something like the alpha systems aoa uses... in case anyone wants to run AOA without a dynon pitot:

Angle-of-Attack-probe-1-HR.jpg
 
Brantel said:
Mike,

We will make it open source and post all the info you would need to build your own educational project right here.
Click to expand...

I think you might be seriously underestimating the level of my incompetence when it comes to things in the electronic/computer world.
 
Whoa Nellie!!!!

Well we may have to put the brakes on in respect to this project.....

Looks like in the US it is illegal to build something that is patented even for your own personal use. (at least that is what I understand)

I have been studying the patent 6,271,769 B1 and it does not leave much room for us building an open source AOA device similar to the one proposed above.

I don't know enough about patents to even begin to know that if we did what is proposed, would it infringe on this patent or not.

What I do know is that I really appreciate Rob and his company and what he has done in the experimental market to bring awesome products to the table. I would never want to do anything that would negatively impact his sales.

So that is where it is at for the moment.....any patent attorneys or someone with significant experience with them want to chime in on the subject?
 
The Jim Franz AOA patent is not a very good one. Its very easy to circumvent with some changes in architecture and software. The killer part is if you got a nice letter from an attorney saying you are in violation of the patent, do you have the time/effort/reason for putting up a challenge? If one were a corporation selling thousands of them it might be viable, but for a project like this I doubt it.
 
I hear you Bob, I don't have the resources to fight something like that so that is the reason for the pause....
 
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You won't have to fight anything.

Go ahead with your project. The worst that can happen is you get a letter from some company's lawyer claiming patent violation. If so, you quit working on the project and write a letter back, stating so. You take down whatever website and materials you posted, end of story.

It's an interesting project, though I have in mind something a bit more involved. I'll PM you to see if you're interested.
 
Buggsy2 said:
You won't have to fight anything.

Go ahead with your project. The worst that can happen is you get a letter from some company's lawyer claiming patent violation. If so, you quit working on the project and write a letter back, stating so. You take down whatever website and materials you posted, end of story.

It's an interesting project, though I have in mind something a bit more involved. I'll PM you to see if you're interested.
Click to expand...

Always interested in a fun project...
 
I would love to have an AOA in my RV-9A. I can solder wires and machine parts but programming is not something I know much about. If this gets to the point of someone like me assembling one I am all in. Sounds like a neat project. Always interested in learning something new.:)
 
"There will be two calibrations to account for flaps and no flaps. I plan to use the Arduino serial port to monitor the G3X's datastream for the flap position in order to not require an additional flap deployed switch. "


Correct me if I'm wrong, but isn't AOA going to be the same regardless of flap position? In other words, if you calibrate it clean, the speeds that will correspond to a particular point on the AOA curve might change with flaps, but the angle will be the same relative to the stall... 1.5x clean stall speed vs 1.5x dirty stall speed ought to report roughly the same angle I'd think.
 
The flaps do alter the critical AOA. Some systems just simplify it to worse case but others do have two or more configurations.

It also depends on what type of flap you have. The RV6/7's flaps alter the lift for about 20degrees and the rest is just drag.
 
Consideration of vibration, temperature and moisture on the hardware is obviously important. Here's some anecdotal info on "potting" electronics which may be useful for this project:

Look up conformal coating ? it isn?t expensive.

If you have a reasonable supply of water, you can produce boards as good as any manufacturer who doesn?t use a clean room.

After you make the board and shield the IO/Power connectors, you need to obtain some saponifier.

These make water wetter and can be bought from many places in small quantities.

It is amazingly close to a certain dish detergent that leaves things ?virtually spotless?, and which works well enough for most purposes if you have access to dishwasher. In either case, run the boards through a dishwasher and dry them.

Then bake them in an oven @200F for a while (think about your solder?s melting point and work backwards) ? or set it to 125 or 150 and leave it for a few hours. The goal is to bake out any residual moisture.

After that, purchase any conformal coating ? it?s sold as such, and comes in a spray can. One or two coats and air dry is adequate. Wait a day or more if you can ? everything out-gasses.

Then ? and only then ? do you pot the product.

For high vibration, you use epoxy, for high chance of corrosion/water/etc, use silicone. For inserting it into a body, medical grade silcone.
You can even do both.

A little foam or rubber around the edges helps with vibration isolation ? much more than simply bolting it down. If you have flexible leads that come from the board, knot them and then mechanically secure them to the board with a screw or bracket or hold-down that doesn?t permit movement. This prevents water from sneaking in.

Finally, you might bake the whole thing at a lower temp for a day or two. After that, if you want to shield for RF, thin copper (You can use steel or brass as well) foil origami with soldered seams will have you ready to take on sky net like a pro.

Need to verify that you?re turning out decent electronic hardware?

Pressure, temp and steam test ? old fashioned pressure cooker. Good for a couple atmospheres.

Vacuum/High altitude is harder, but you can get close with almost any vacuum pump and an old pressure cooker body. Or find a used commercial vacuum chamber. You can make one, and use multiple pumps to overcome your sloppy workmanship.

Vibration: Anything that shakes. Car frames work well, especially if you drive off-road or your city is too poor to care. Sweet talking someone with a paint shaker [really excellent] is easier
if you mount your device securely in a paint bucket and stay away from big chain stores.

Be sure to check at several regimes ? the hitachi giant wand/lawn mower deck/paint shaker trio will uncover almost anything.

Finally, RF ? go find someone with a 2 stroke dirt bike not made in japan and try to run your project board attached to the frame with the gnd lead attached to the frame. That will separate the men from the boys within two minutes.

When your project survives all this, it will be suitable for almost anything from submarines to low earth orbit. A good final test is to let your dog/children play with it for a quick game of fetch/keep away.
 
Very cool. I'll be eagerly watching this thread. We really will need a simple probe for those of us without Dynon. Will all the machinists in the group I don't doubt someone can whip one out quickly along with some sort of nice housing for the light display for the top of the panel.

Wow .. I love open source and creative people!

DWS
 
My sensors have arrived and I am now awaiting some tubing before I can build a test rig to be able to test this thing by sticking it out the window of the truck while my wife drives me down the interstate.

Here is what it looks like so far:

2i7vm1u.jpg


A bit of sample output while in development mode:

vdq1q1.jpg


So far the code is pretty simple.

Temperature compensation is built into the sensor so I do not have to worry about that.

I have developed a way to automatically cancel out the zero error that all of these type of sensors have to get both sensors on the same bias. Not sure if I will make this automatic at startup or require some sort of operator action to trigger it.

More to come...
 
Been working on this a little at a time in the evening and during lunch.....

Here is a video that shows where I am at:



First you see the hardware then you will see me blowing into the Pitot line and the results are shown on the LCD screen. Basically a pure Pitot input results in an IAS increase and a negative AOA %.

Next you will see me switch lines and blow into the AOA line and the results on the LCD and the results are shown on the LCD screen. Basically a pure AOA input results in an increase of the AOA%.

Finally you will see me switch to both lines and blow equally into them and the results are shown on the LCD screen. Basically an equal pressure to both results in a 0% AOA and an increase in IAS. The IAS cancels out the AOA% increase.

So now I am left with the challenge of developing some sort of calibration routine for setting the scaling of the LED's to the % of AOA. They are currently scaled linearly across the range of 0-99%. Any of you expert programmers have any suggestions of how to accomplish this task? Looking for different ideas so we can pick the most efficient one.
 
Cool project. Do you have a cost estimate on the current parts?

I've used arduino for some past projects, but have steered clear in the last couple of years because of cost. Using other embedded processors and boards are cheaper though they may be a little startup time for development.
 
Brian,

Are you powering your Arduinos straight from ship's 12V or are running them through a voltage regulator? I see the Uno is rated up to 20V but I'd rather not fry mine checking it.
 
There are several types of boards out there but yes I run my UNO and Mega straight off of ships power.
 
Brantel said:
There are several types of boards out there but yes I run my UNO and Mega straight off of ships power.
Click to expand...
Thanks, makes it a lot easier. Cobbled up a GPS logger tonight, I guess I'll test it without a regulator tomorrow.
 
AOA Solution

This thread was brought to my attention by a friend and I thought I could help. I'm going at risk here since we are not an advertiser on Vansairforce, at least not yet, but I'll try it anyway. I think it's great that you're looking into AOA. AOA is an enormous safety benefit and every airplane should be equipped with it.

There are just a few points I wanted to make.

First, Alpha Systems AOA is a stand alone system. It does not require sharing the existing pitot/static system. If something were to happen to the pitot/static system and fail or malfunction, Alpha Systems AOA will continue to perform normally and can be used to help safely guide you out of trouble.

Second, Alpha Systems AOA does not need any additional holes to be cut into the skin of your airplane as the static port style of sensors require. The probe mount replaces an existing inspection cover making installation simple. And it protrudes no further than a pitot tube, about 3 inches.

Third, functionality features are built into the display, no additional panel space is consumed by switches or buttons and the display orientation options allow unlimited mounting options.

Finally alphasystemsaoa.com has an unconditional warranty. If the product doesn't do what we say it will do, you get your money back.

-Chris


[ed. Chris, I emailed you advertising info. Let's talk. Kindest, Doug]
 
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Welcome to VAF!!!!

Chris, welcome to VAF:D

Your system sounds interesting, will be watching for more info.
 
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