Kite power

What is the best way to get electric power to a kite? I need enough to power a small CMOS camera, and small motors that aim it. I also need to intermitantly
power a larger motor that steers the kite. This is a BIG kite, about 2 meters by 4 meters, so it will be tethered by a rope, not a wimpy kid's kite string. My plan is to fly it over 1000 meters up (anyone know what the FAA limit is?), so the rope will need to be about 1500 meters long.
I don't want to use a separate wire, because it may get tangled, and will cause more wind resistance. So I am thinking of weaving a pair of wires into a nylon or kevlar rope. Anyone know if something like this is already available?
I could use a solar panel, but that will add weight, and won't work if it is cloudy or at night.
Another idea is to attach a mini-generator to a little propeller, and generate power from the wind. But my concern is that to provide enough power it will have to be too heavy.
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Bob wrote:

Lithium Polymer batteries weigh next to nothing an have plenty of power to run two R/C servos and a CMOS camera for hours, probably even including a HF transmitter to get video images to the ground. One and a helf kilometers of copper wires is definately heavier.
Besides the FAA, you might want to check what permissions you need for aerial photography from that height.
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Matthias Melcher wrote:

And besides that, who wants to be flying a kite connected to the ground with a wire?
Mitch
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"Mitch Berkson" wrote

Ben Franklin? 8^D
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Mitch Berkson wrote:

Good point, use wire in the string and you could have PLENTY of power. Especially if the wind dies down and the wire drapes over some HV power lines.
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"cbm5" wrote

In Brazil (my country of origin) a very popular sport amongst male teenagers is kite fighting. They don't look like these fancy kites we have here in the USA. They look like a pentagonal shape made with bamboo sticks and paper and a long tail made of plastic ribbons (cut from plastic bags). These kids develop amazing control skills and perform really nice aerobatics with their kites. The fighting consists of cutting the cord of other kites (of course while in the air) and retrieve the now loose kite to the winner's hand. In order to cut other kite's cords, they apply a home made preparation made of glue and glass smashed in very fine particles to their kite's line (of course every kid has it's own "secret formula"), which I believe increases the electrical conductivity of the cord. During summer months, it is very common to hear about kids being electrocuted when their kite's lines touch the HV power lines. (as it is common the news of dead motorcyclists who had their necks cut from these cutting lines)
Cheers
Padu
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Mitch Berkson wrote:

Well, then, that certainly answers the question of power doesn't it. Even on a sunny day, correct me if I'm wrong, some potential exists between ground and some altitude.
Y | | | Kite as antenna |______________L1 \ | / | \ R1 --- C1 / ___ \ | /________|_______L2 | | Wire to ground | | _____ ___ _
Take L1 and L2 and feed them into an H-Bridge rectifier, make sure you have some sort of surge protection before the rectifier. R1 prevents voltage buildup. C1 does some filtering and maybe spike protection.
Obviously, you won't be flying this sucker during a lightening storm.
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Bob wrote:

Well, you may want to consider weight, 1000 meters of wire is pretty heavy. A radio link may be lighter.
If you consider 26ga wire without insulation is about 3/4 pound per 1000 feet, you are looking at maybe 3 or 4 pounds per wire and insulator for your 1000 meters. If you have two wires, that's between 6 and 8 pounds.

A permanent magnet motor makes a great little generator, get it spinning fast enough, regulate it down to a manageable voltage and feed it into a few NiMH batteries.
I would look at two things, first, the payload capacity of the kite. It would be useful to know this. Second, you need to know the power requirements of your electronics.
Once you know these two things, you can figure out your options.
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I wonder if you've really thought this through. First of all, one of the first rules of kite flying is never include a conductor as part of the tether. In addition to the obvious "if it drapes over a power line, you're a crispy critter" aspect, it's generally bad to send long conductors up hundreds of feet, asking for a lightning strike.
Furthermore, it doesn't seem like you need anything more than simple battery power (lithium polymer batteries are especially light) to power a small cmos camera and enough servos to aim the camera.
    Mark
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One presumes that there's a good wind blowing when the kite is aloft. I would start thinking about a small BLDC hooked up as a generator. Main power should come from batteries. Use the generator to keep the batteries continually charged.
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Well besides the obvious dangers, I belive you could use a 32 gauge wire pair. You could run 300 volts at 10ma At that voltage the resistance is almost negligable. then on the kite use a light weight ( high frequency ) step down regulator to create 6 volts at 400 ma
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    --OBTW there's an article in a recent issue of Make magazine that goes on at length about kite photography. They're new and only up to issue #4 so it shouldn't be hard to figure out which one.
--
"Steamboat Ed" Haas : Whatever happened
Hacking the Trailing Edge! : to Pasquale Gumbo?
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