Subject:
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RE: "real" LEGO Hovercraft ? (with/without batteries/RCX "onboard")
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 1 Dec 2002 06:19:51 GMT
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Original-From:
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Rob Limbaugh <[RLimbaugh@]nomorespam[greenfieldgroup.com]>
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Viewed:
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822 times
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Brushless DC motors, such as those used in PC cooling fans, won't generate
enough power, even if the voltage is increased. This is because they actually
have a switching circuit that changes polarity of the electromagnetic coils.
I've gotten a small (less than 1 square foot) piece of foam board to hover using
an older 12v fan with brushes and two 9v batteries in series.
Doesn't the thrust fan also have to overcome air leaking around the edge of the
fan blades and the thrust fan shroud?
> -----Original Message-----
> From: Steve Baker [mailto:sjbaker1@airmail.net]
> Sent: Friday, November 29, 2002 3:36 PM
> To: PeterBalch
> Cc: [unknown]
> Subject: Re: "real" LEGO Hovercraft ? (with/without batteries/RCX
> "onboard")
>
>
> PeterBalch wrote:
> > I just tried
> >
> > a 5V processor cooling fan
> > a 12V computer PSU cooling fan
> > a 3V ducted fan of the sort used to cool your face
> > (run at 5V without on-board batteries)
> >
> > with a 16cm dia polystyrene plenum.
> >
> > None could really lift their own weight - although the • processor cooling
> > fan just became a little easier to move.
>
> I think you need a MUCH bigger area under the craft. If all the
> motors and stuff on top weighed (say) 100 grams, and you have just
> 16cm diameter skirt then you need a pressure of:
>
> 0.1 / (PI x 0.008 x 0.008 ) kilograms/square meter
>
> ...in order to have it hover.
>
> If you double the diameter of your skirt, you'll only need one quarter
> as much pressure! If you could build a light enough skirt that was
> 100 times bigger (1.6 meters in diameter), you'd only need one
> ten-thousandth the amount of pressure to make it hover!
> ---------------------------- Steve Baker -------------------------
> HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
> HomePage : http://web2.airmail.net/sjbaker1
> Projects : http://plib.sf.net http://tuxaqfh.sf.net
> http://tuxkart.sf.net http://prettypoly.sf.net
>
>
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