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HelicopterAerial Photography and Video › need feedback on this Altitude hold board
08-10-2007 10:29 PM  10 years agoPost 1
46Taylorcraft

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AZ

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http://www.u-nav.com/circuitboards/alt3.html

They say not to use it with heli's on the website because of rotorwash pressure inaccuracies, but my Zlog does fine when mounted in a ported plastic box.

I'm thinking of throwing one of these on my Logo 10 test ship.

Any opinions, ideas, warnings?

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08-10-2007 11:08 PM  10 years agoPost 2
Disciple4123

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USA

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Yes, it is something I am planning on putting on an airplane system within a year (with the GPS to base device). Testing it on the heli first has crossed the mind as well, do we know if it has a pipe out, or just internal reading. At least I could pipe a line out the boom, 6" past on a small fiberglass pole, this hose would read air that is somewhat out of the rotorwash??

I know Carvec uses baro alt lock, and I've seen plenty of video results of it working within a meter, so conceptually it is proven. Now as far as gain tuning, sensor accuracy, plumbing, and the like, I'd say it may take a little R&D to adapt the UNAV.

Try it DJ, you seem to accomplish most everything else you try

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08-10-2007 11:24 PM  10 years agoPost 3
GauchoVolador

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Tx

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DJ,
It seems to be an old fashion barometric sensor that is probably why it is affected by rotor downwash, sensor itself accuracy is 1ft and +-20ft the altitude hold resolution.
Im testing a MEMS barometric sensor with less than 4 inch resolution, still working on the software.

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08-11-2007 12:55 PM  10 years agoPost 4
ssozonoff

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Switzerland

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This was the coversation I had with the UNAV guys.
Serge,
Yes we've had a few customers try the ALT3 on heli's....that's why we don't recommend using it (on heli's).
You're welcome to try it but the warranty is void for that application (ie. no returns).

Mark, Sales
UNAV, LLC

----- Original Message ----- From: "Serge Sozonoff" <serge@sozonoff.com>
To: <mark@u-nav.com>
Sent: Monday, May 07, 2007 11:37 AM
Subject: ALT3 and a Heli

> Dear Sirs,
>
> I know you don't recommend the Alt3 in a heli but I am thinking that
> there must be a way to mount the thing to avoid turbulence from the main
> blades. Do you know of anybody who has tried the Alt3 in a heli?
>
> Kind thanks,
> Serge
>

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08-13-2007 10:19 PM  10 years agoPost 5
lele

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italy

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Well...

I have ordered one and it's been some months I received it, but never had time to test it. I will probably make a test this week on a T-rex 450 ccpm, I will connect the ALT3 to the 6th Ch. between the RX and the Helicommand. I will make sure to be very high before giving it a try!
I am not planing to test with a pipe out of the boom because I have seen that some others altimeters (although not controlling the elevator but only for video overlay) are working fine if the sensor is protected by some foam. In any case I have already bought a plastic pressure pipe to test that one too.

Does any of you have any idea if the ALT3 (I have the ALT-E type) out-put works in P(proportional) or PID (proportional-integral-derivative) that is a great difference in out put control, if it is only Proportional I am expecting some great oscillations from the heli trying to follow what the sensor out put is.

Anyway for the first test I will go with almost zero gain...and let's see...

As soon as I test I will post..
Any suggestion before I test would be appreciated!

thanks
lele

To be correct: Unav that is the producer of the ALT3 device kindly advised me against the use of their device in helicopter since it was not developed for that. I am aware that I am doing a test on my own risk.

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09-09-2007 09:21 PM  10 years agoPost 6
Disciple4123

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USA

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Any results on the test Lele?

Thanks,

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09-09-2007 09:42 PM  10 years agoPost 7
lele

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italy

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I was to try but,

once everything was connected properly (the alt was between the 6ch and the helicommand) there was no way of having it (the Alt) turned off, it's led was always on. And that is bad! since it means that the ALT is the only one having control on collective! I renounced to test it also because the manual says that you should feed it with 6V and that is not my case since my bec gives only 5,4V. Anyway it seems strange to me that one could not turn it off remotely because of the 5,4V, could my ALT be defective?
I also bought from the UNAV the pico-tilt board and that was not working with Futaba PCM signal requiring an FMA Direct buffer, have to say that even when the buffer was connected and the Pico-Tilt worked I was very disappointed of it's jerky performance.
I did not think of testing the ALT with the buffer, since I can't think of having so many items all connected to such an important channel as collective is.
As soon as I will have some spare time I will make some bench tests to see if it could work with the 6V.
Sorry for not having any better informations.

Lele

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09-10-2007 01:06 AM  10 years agoPost 8
Disciple4123

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USA

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I don't know if yours is defective. My plan is to evenutally use that device ALT3 and RTL "return to launch" to operate a powered glider for UAV. So I have looked into UNAV over time, and it seems that some people are happy with them on the rcgroups forum.

Are you running Futaba 2048 resolution? Perhaps there are interactions as the 2048 I hear is very finicky, I just use a JR9303 w/2.4 module.

And it could be the undervoltage you are discussing, if I was designing such a product I'd try to accomodate the 4.8's and 6.0 systems

Thanks for the information.

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09-10-2007 01:40 AM  10 years agoPost 9
ErichF

rrElite Veteran

Sutton, NH

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The best way to stabailize a static altitude sensing system is to use two ports, one on each side of the aircraft. The two ports are tee'd together at the exact center, and the 3rd line connected to the static sensor port.

The way it works is, any turbulence or pulses introduced to one port pass straight through the tee to the other port (path of least resistance). You won't have pulses at both ports at the exact same time, as the blades pass one side and then the other. Also, you want to have at least 6 inches of line from the Tee to the sensor, the more the better. This allows any residual pulses to flatten out before getting to the sensor.

Also, if you have a crosswind acting on the aircraft, the sensor will not act like a pitot tube, as ram air pressure from the sideways air movement will pass straight out the opposite port.

A real simple way to do this, is use a small enclosure with ports on each side. If the enclosure is small enough, you don't really need to use any plumbing.

Hope this helps some. This is the method I've used on several UAV conversions I've completed on RC Aircraft.

Erich

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