Subject:
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RE: LEGO RCX Skydivers
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 10 Nov 1999 00:09:30 GMT
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Original-From:
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Jim Thomas <Jim.Thomas@trw.com/nomorespam/>
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Viewed:
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771 times
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Robert's numbers look good, although compared to my numbers they look
conservative by about 10% -- I had 13.4 ft^3 per pound. As far as envelopes
go, you basically have to make one from scratch. It is not really that hard
you just need the right Mylar material and a hobby iron intended for heating
shrink covering for sailplanes (it looks like a small clothes iron on the
end of a handle). The Mylar film that is used in the fancy metallic looking
helium balloons actually is coated on one side with something that will melt
to create the seal. Unfortunately I don't remember what the composition was
or where we got it. To get a nice and smooth blimp shape, construct it
using the same technique as a football.
I'll try to pull some of this together on my website. I'm working on
getting picture scans of the one we built.
JT
> -----Original Message-----
> From: Pete Hardie [mailto:pete.hardie@dvsg.sciatl.com]
> Sent: Tuesday, November 09, 1999 2:15 PM
> To: lego-robotics@crynwr.com
> Subject: Re: LEGO RCX Skydivers
>
>
> Robert Munafo wrote:
> >
> > Either my calculations are wrong, or you have a different • concept of what is a
> > "staggering" amount of helium. Here are my calculations:
> >
> > Each gram-mole of gas at STP [1] takes up 22.41 liters • (cubic decimeters) of
> > space.
> >
> > The weight of a mole of air is about 28 grams (a little • more actually, but I'm
> > being generous), and the weight of a mole of helium is 4 • grams; thus the net
> > bouyancy per mole of helium is 24 grams [2]
> >
> > Net bouancy per liter of helium = 24 / 22.41 = 1.07
> >
> > Volume of a sphere 1 meter in diameter is 4/3 pi r^3, where • r is 5 decimeters,
> > which comes out to about 523.6 liters.
> >
> > So a spherical balloon of 1-meter diameter and filled with • helium would have
> > about 560 grams of bouyancy, or about 19 ounces for you • non-Metric dudes.
> >
> > For comparison, the "fish" blimp that swam around in the • Media Lab during its
> > first year or two was about 2-3 times this volume (same • diameter but about 3
> > times the length)
> >
> > What am I missing?
>
> Mostly my hyperbole....
>
> Still, getting envelopes for that amount of helium is difficult.
>
> --
> Pete Hardie | Goalie, DVSG Dart Team
> Scientific Atlanta |
> Digital Video Services Group |
>
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