h a l f b a k e r yExpensive, difficult, slightly dangerous, not particularly effective... I'm on a roll.
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What about a self winding clock (or clockwork motor) using one of those solar glass 'radiometers' that spin around in sunlight suitably geared.
If you are not sure what a radiometer is, see http://www.physlink.com/estore/cart/SolarRadiometer.cfm
My idea is to drive a clock movement from
the spinning blades so that the clock would wind iteslf during the day and run 24/7. The same idea could be used to drive all sorts of gadgets, you could make the blades bigger to provide more power if needed.
Crooke's Radiometer
http://science.hows...com/question239.htm
[Amos Kito, Oct 04 2004]
Pitch Black.
http://www.rottento...1095092/reviews.php
Aliens, Hot Babes, Vin Diesel, and Radiometers. It's got it all. [Amos Kito, Oct 04 2004]
Dracula's Library
http://www.miamisci...ula/radiometer.html
[angel, Oct 04 2004]
Thermal Transpiration
http://math.ucr.edu...ill/light-mill.html
Yeah, sounds weird, but... [lurch, Oct 04 2004]
[link]
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Watching those things spin like crazy, I've often thought they could be used as a mechanical drive. They're usually on a low friction bearing like the point of a pin. How much torque do you get out of one? |
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The movie Pitch Black [link] used radiometers in toys and generators. |
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They are on low friction bearings but its usually just a glass tube, nothing like the low friction bearings in watches and clocks. I suspect that the output power is very high,as you say they whiz around like crazy and in strong sunlight they can even vibrate enough to move!
One obsticle is the fact that the are contained in a vacume (you wouldn't want to evacuate the whole clock!), so I propose the use of 4 small magnets attached to the blades they could be used to transfer the momentum out side the sealed glass container, then you could slowly wind a small mainspring, over the course of several hours. It is interesting to note that they also work on a cloudy day providing the daylight hits them, so I think the power is there! |
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Anyone know if making the blades bigger would give you correspondingly more power? or is there a finite limit to the amount of thrust that can be generated? |
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I would have thought they are more effieicent than solar panels since the energy goes direcly into momentum, rather than converting to electricity and then driving a motor |
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What he said. Over time, even the tiny amount of air within the bulb stops providing much drag, as it gets to spinning along with the blades. There is a little friction drag with the walls of the bulb that slow it just a tiny bit, but not much. The radiometer works purely on heat. As the black face heats up slightly, the air molecules on that side of the paddle will move faster and hit that face harder than the cooler air molecules on the white side, yielding a net positive torque. This torque is extremely small, and it is doubtful that any meaningful work could be extracted from the system. |
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Pffft. You with all your "scientific evidence" and "laws of physics". Hooey. If Vin Diesel says it works, then it works. Period. |
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//The radiometer works purely on heat.//
I think you'll find that it works on light. I've just activated mine with a little 3V flashlight shining through an empty coffee jar. |
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The effect ("thermal transpiration") that moves the vanes only applies on the edges of the vanes. I find it odd that the design of the radiometer has never changed from what was originally intended to demonstrate photonic momentum. Vanes with slots, or, even better, a large number of small holes, would produce substantially more torque. |
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It would take some careful engineering, but I am reasonably certain that a way could be developed to capture the rotational energy. (My first impulse is to use regenerative braking, only tapping the energy when the rpm's climb above a certain level.) |
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Sealorator, thank you for clarifying my statement. Lurch, the effect does not act only at the edges, it acts across the entire surface of the blade. |
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// does not act only at the edges, it acts across the entire surface // Nope. Very common misconception; see link. |
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I will be doing some experiments on this as and when time permits, I will report back when I get somewhere. |
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Thanks Lurch for the idea about putting fins or holes to improve performance is inspired nice one dude! |
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Perhaps abandon radiometer altogether and create a solar stirling rotary engine using vanes. The vanes could be painted white on one side/dark on the other for heating and cooling cycles. |
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The radiometer has 'nothing' to do with sunlight and is basically a variant of a stirling heat engine.
There are current experiments in progress to extract substantial power from these kind of devices. |
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Lunatrick... instead of using magnets the approach that's currently being taken is not only to add holes, but to have a horizontal fin on each vane to give the assembly lift and have it levitate on it's own. |
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