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Old Oct 06, 2005, 05:36 PM
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The High Altitude Slug Project - A cheap high altitude UAV!

http://glider.phatmonkey.org.uk/

If anyone's interested in the project we're working on! We're quite a way in and have almost everything covered.
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Old Oct 06, 2005, 06:32 PM
Professor of Wood
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Nampa. Idaho
Joined Nov 2004
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Quote:
Originally Posted by phatmonkey
http://glider.phatmonkey.org.uk/

If anyone's interested in the project we're working on! We're quite a way in and have almost everything covered.
phatmonkey,

Here's some pictures of a mechanical cutaway device I designed that uses a micro servo. This would allow your cutaway to work with your existing flight computer and servo power system. I use a P channel mosfet to power the servo at cutaway time then power it back off for energy conservation.

http://www.tvnsp.org/modules.php?set...view_album.php

I have run up to three servo's in this high altitude capsule without the mosfet switch with no troubles. It features a servo to watchdog the GPS, a servo to perform the mechanical cutaway, and a servo to deploy the chute before impact.

http://www.tvnsp.org/modules.php?set...view_album.php

We use Nimh (older capsules) or LiIon batteries. We haven't flown Lipo's but we know you can freeze the dogsnot out of LiIon's and they'll still perform. Nicds and alkalines freeze up and quit at about 32f. Oops, I mean 0c.

Keep us posted. I'm curious if a thermopile calibrated at ground level will still work when it's at -60f or colder with the sky black and the earth curving away. For the same reason as you as a matter of fact. I'm not working on my glider yet though. Let me know if there's anything we can provide. It's cool stuff. Feel free to peruse our site.

http://www.tvnsp.org/index.php

Dan
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Old Oct 07, 2005, 05:13 AM
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That looks like a very good idea actually. We used a similar thing on a kite release mechanism. It would have been useful if the kite ever got off the ground!

Does the pin hold up well under extreme loads? If it gets bent, it will probably jam, won't it?
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Old Oct 07, 2005, 10:24 AM
Professor of Wood
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Nampa. Idaho
Joined Nov 2004
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The T pins we get in hobby shops over here are stainless steel. They are very strong. We load tested one of those units in my garage with 25 pounds hanging on it. I also grabbed it by hand and pulled even harder and still activated it. I don't know how hard the pull was but it was running the lines painfully deep into my hands. Maybe 50 pounds? It activated just as easily as with no weight. It's harder to bend that pin than it is to bend an equal diameter of piano wire. Look at the mechanics of the device not just with the pin holding the nylon bellcrank, but the angle the bellcrank sits at when under load. It's tipped downward at ~45 degrees to the upward pull. That slides the lions share of the load towards the hub of the bellcrank and the steel bolt. There isn't much of a load on the steel pin this way and no load at all on the little servo. It takes the leverage moment away from the force of pull. Also, when the capsule gets powered up, an initialization piece of code seats the pin as one of the processes. That pin goes through the far wall for flight. It is supported by passing through both walls around the bellcrank. The holes drilled in are just big enough to allow the pin to slide freely. On that last picture in of the devices you can see a small block glued on where the pin exit hole is. That covers the tip of the pin just so no one gets poked by it when it's stowed into the flight position.


I use a micro controller called the Basic Stamp 2 from parallax to activate it. I write the code so it just pulls the pin far enough to release but not all the way out of the wall of that unit. You can see I doubled up the material where the pin enters at. This does two things. It keeps the single wall from getting wallowed out, and it gives me more room to pull the pin so I'm well clear of the nylon bellcrank.

I plan on putting one of these in the tail of my glider when I get to building it.
It can be done much lighter than the nicrom wire method that has to bring it's own power supply. We have flown these or some version of these to in excess of 100,000 feet routinely for the last two years. They work flawlessly as long as you write the code to the servo well. Give it at least 50 pulses to clear. I tried using a byte on the first flight but it didn't pull it far enough. Things slow down when they get that cold. It worked on the ground without fail but didn't pull far enough at the 75,000 foot test flight. I give them a full word now and over do the pulse count. You can go to 256 pulses if you want to. We have code that cut's away at specific altitudes but also watches the GPS altitude. If a descent is detected, it will still cutaway. Just in case the balloon pops before it's predicted to.

I agree that this has to be done. You can't trail that mass of latex on a load line and expect a glider to glide. This is a good means to unfetter your aircraft.

Dan
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Last edited by kd7ost; Oct 07, 2005 at 10:38 AM. Reason: added info
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Old Oct 07, 2005, 10:43 AM
I AP'd myself again......
aviatordave's Avatar
Yawn....Iowa
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Dont you want to protect your page, I can go in and edit everything - can anyone else see that?
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Old Oct 07, 2005, 11:57 AM
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Yeah, it's a wiki. That's one of the points of it really, people can add their information and things (seen Wikipedia?). Vandalism is surprisingly low.

Thanks for the help on release mechanisms, we'll probably use something like that. It'll be much simpler and more reliable (but a tad less strong) than melting it.
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Old Oct 07, 2005, 12:10 PM
Professor of Wood
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Nampa. Idaho
Joined Nov 2004
4,266 Posts
Quote:
Originally Posted by aviatordave
Dont you want to protect your page, I can go in and edit everything - can anyone else see that?
Yep, It was set up so everyone in the group could add, edit etc. We haven't had any problems. Generally everyone that goes there is kinda scientific and all.

Maybe I should be more careful about posting it here?

Dan
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Old Oct 07, 2005, 12:51 PM
I AP'd myself again......
aviatordave's Avatar
Yawn....Iowa
Joined Mar 2005
2,500 Posts
Oh in that case its a good idea, if you get vandals, just erase it....usually vandals are too lazy to check out sites like this anyways.

cool work guys.

-Dave
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Old Oct 07, 2005, 04:11 PM
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United States, TX, Wimberley
Joined Mar 2004
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Hey Phatmonkey,

Looks good man.. Glad to see some more guys doing research with wings!

Myron
www.rpflightsystems.com
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Old Nov 12, 2005, 07:28 PM
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UK
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We're now working on an uncontrolled payload to test various things (included IR horizon detectors!). I have made a mechanical release mechanism very similar to yours, kd7ost.
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Old Nov 12, 2005, 09:42 PM
Professor of Wood
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Nampa. Idaho
Joined Nov 2004
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Hey, looking good.

I'm very interested in how the IR (Thermopile?) sensors work at high altitudes. What do you have in mind for the upcoming flight test if it's not a trade secret. Thats the main reason I haven't launched a glider yet. I don't know if roll and pitch stabilization will be maintained by the co-pilot and need to test the same thing as you.

Dan
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Old Nov 13, 2005, 06:16 AM
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http://glider.phatmonkey.org.uk/wiki/Atlas

I will probably just throw on as much stuff to test as I can, since weight is not much of an issue. I will just record all raw input from the IR sensors for processing and analysis later.
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