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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Tue, 26 Nov 2002 23:32:18 GMT
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Original-From:
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Jim Choate <ravage@einstein.!spamcake!ssz.com>
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Viewed:
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2238 times
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On Tue, 26 Nov 2002, Chris 'Xenon' Hanson wrote:
> Ground effect vehicles require quite a bit of power-to-weight, and I'm not
> sure if this will fly. I suspect you'd have to cheat and use a more powerful
> motor/rotor combination than pure Lego can offer.
Actually they don't. You can create a hovercraft that will lift an
ordinary adult (say <200lb US) using nothing more than a half sheet of
plywood, a 1/4HP vacuum cleaner motor, a shower curtain, some tape, a
bunch of 1" washers to keep the groundside skirt down, a staple gun and
assorted hardware. If you scrounge the vacuum motor the whole thing is
less than $100. Takes about 4 hours to build. Mount the motor in the
center of the board with the exhaust blowing downward. You -will- want to
pleat the corners to get a good curved shape. Talk to somebody that makes
clothes for hints on how to fold if you can't figure it out yourself.
For Lego the optimal solution would -probably- be to use a tubular skirt
with holes in the bottom. The problem with a 'open plenum' design is so
much air gets lost and it really sucks in turns (the inner side of the
skirt dips while the outer lifts off the ground). The tubular skirt allows
you to maintane consistent distance between the ground and the 'running
board' of the hover. At the bottom of the tubular skirt you want to put
small holes for the air to excape (it might be better to put them slightly
up radius on the inside to help initial inflates and during turns -
experiment). Where the fan exhaust comes through the running board you'll
want another plenum. I'd use a smaller flat plate and some stand offs.
Then use the little tubes (one of the few non-decorative use of these
things in Lego robotics) to route air into the skirt. I'd use four (4) to
start, feeding front, back, R/L. Seal it with a hot glue gun.
As noted, the biggest problem is going to be air flow. The Lego motors
might work but I doubt most of the plastic 'propellers' have sufficient
efficiency. In addition the blades probably aren't sufficiently stiff to
handle the air flow without a lot of flexing (and that will dump a lot of
your air around the end of the blade in low velocity flow - something you
don't want). I'd go with something like a model helo tail rotor. The Lego
motors probably have the speed, but do they have the torque?....
--
____________________________________________________________________
We don't see things as they are, ravage@ssz.com
we see them as we are. www.ssz.com
jchoate@open-forge.org
Anais Nin www.open-forge.org
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