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Mr.RC-Cam

Artificial Horizon

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Okay, here is my turn (at last).

I just come back from a 2-week holiday with a friend at the seaside in France. Of course, it wouldn't be holidays without having planes, so we each had a parkflyer, and we took our new 1.90m wingspan RPV (simple cheap trainer, but with a huge fuselage with enough room for lots of nice stuff :P ) so we could build it there.

It was equipped with a 100mW TX, 620-line CCD on a servo, 4MP digital camera, TL100, and of course the MAHI ;)

We also added a second TX with a KX131 for a different viewing angle (on the rudder).

So, test results: Very nice, no glitches, really like we would expect it.

Wouldn't be normal if it was 100% OK, we just had strange black trails at the right of the MAHI graphics, but that was not really disturbing (see capture). I noticed that if I swapped the MAHI and TL100 in the chain it behaved a bit differently, that is the pitch display appeared 3 times aside. But I suppose that this must be due to the length of the video cables disturbing a bit the sync. Could this be right? At least it didn't happen when I had wired the stuff without the TL100 the first time on my desk.

I must say that when flying in FPV mode with the camera on a tilt servo it's really cool to be able to see if you are still flying level :)

We just noticed that the MAHI had some difficulties when facing the sea, but that's normal, question of temperatures... what was funny though was that the pitch indication seemed more sensitive to this than the roll one...

Well, thanks again for this ;)

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Congrats -- It's good to see that your MAHI is finally up in the air. The ghosting in the video graphics is an indication of signal ringing. It could be Tx's video cabling, or your video transmitter, or even the video Rx's end of things. Since MAHI's graphics appear to be affected a lot, you should be able to mask the ghosts a little bit by increasing MAHI's R10 value (currently 22 ohms). Higher values will reduce MAHI's brightness, so don't go crazy with it. Start with a 50 ohm and go from there.

BTW, the vacation area shots look great.

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Okay, will try this. Will also try reducing the cable lengths, as they are too long anyways.

Yeah, it was really a great place, and we've been lucky as the beach where we were flying atually is restricted to local residents, so we had plenty of space and nobody would come and ask thousands of questions per second... :P

Also been experimenting hydroplanes by taking off from the swimming pool :)

And BTW, the KX131 stands salted water as long as it is rinsed with clear water and left to dry for half an hour at the sun :lol:

IMGA0697.jpg

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A question regarding thermopiles….

I see that there are phototransistors availed that have IR bandpass filters on them. The filters pass wavelengths from 700um to 1100um which is the same range thermopiles function in.

I was wondering why we (or the Copilot) can not use IR phototransistors instead of thermopiles. They both function in the same band of wavelengths. It seams that a phototransistor would have an output proportional to the IR intensity just like a thermopile.

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Can you post a link to the data sheet of the phototransistor candidate? I would like to see what you had in mind.

Phototransistors that have the IR wavelength sensitivity you need are typically expensive, whereas thermopiles have traditionally been cheaper to use and required less complex instrumentation interfaces. But perhaps things have changed.

I see that there are phototransistors availed that have IR bandpass filters on them. The filters pass wavelengths from 700um to 1100um which is the same range thermopiles function in.

I have a feeling that the phototransistor wavelength specs you saw were 700nm to 1100nm (that is, nm instead of um). Thermopiles are typically 5-15um. For the Co-Pilot-like sensing devices, I understand that the 2-100um spectrum is usable.

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Good catch, you are right. I got my nano and micro mixed up. I new it seemed too good to be true (the phototransistors I was looking at were $1.20) I suspect that these are what the Futaba PA2 copilot uses though.

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Someone mentioned earlier they could draw up the schematic of the FMA sensor unit (the block that contains the four thermopiles and has the proportional voltage output).

I am trying to make my own version and would like to see what their circuit looks like. Can someone please draw up the FMA circuit for me.

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I looked on the site but I was unable to find it so I emailed them. As soon as I hear from them I will post it here.

I was wondering if you could give me your engineering expertise:)...

I am making a 3 axis sensor instead of a 2 axis like the FMA. This means I will have 6 thermopiles (two for each axis).

My question is, which would be better to do.

1) Have one voltage output for each axis, like the FMA does (3 total outputs)

2) Or have 6 output voltages, one for each sensor (6 total outputs).

3) Or maybe it does not matter

My goal is to make an artifical horizon on a ground PC through an RF link.

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I vote for #1. It might be best to start a new thread on your project to keep this discussion dedicated to the MAHI project.

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cyber-flyer,

You said you could draw up the schematic of the FMA sensor block a while back, would you mind doing that for me.

I heard back from the guy over at http://autopilot.sourceforge.net. He said he does not have the schematic :(

What are other peoples opinions about my question two posts above.

Edited by jheissjr

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Using Google, I found a schematic to the 2-axis thermopile sensor on the UAVS.net site: http://www.uavs.net/schematic.jpg

What are other peoples opinions about my question two posts above.

(1) Fewest required ADC inputs, inherent common mode rejection and ratiometric operation.

(2) 2X as many ADC inputs and instrumentation OpAmps. No common mode rejection.

(3) See the two comments above.

EDIT: Jheissjr's 3-axis thermopile project discussion has moved to here: http://www.rc-cam.com/forum/index.php?showtopic=989. Please continue to use this thread for MAHI project remarks.

Edited by Mr.RC-Cam

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