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Marco Correia wrote:
> 3) Is there a LEGO-only way to generate enough air flow (pressure) ?
> One solution to "trap" the air underneath the unit is to build a LEGO
> framework (as light as possible) and then use plastic film (that used to
> keep vegetables fresh etc) to create something like the bottom of an
> hovercraft.
> ...I'm going to make some tests at home, but I don't think it'll work. But
> at least I tried :)
I'd be interested in knowing how this works.
The ZNAP green helicopter set (which I got three of last year at $9 each!)
had some little round turbine-like parts, basically a ducted fan. Never tried
them out to see if they're actually aerodynamically functional, but if they
were, you could put them in vertical ducts, driven by the ZNAP flexible drive
shafts to float the skirts.
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.
> mc.
Chris - Xenon
--
Chris Hanson | Xenon@3DNature.com | Life is too short to fold socks!
New World Construction Set 6 Demo Version!: http://www.3DNature.com/demo/
"There is no Truth. There is only Perception. To Perceive is to Exist." - Xen
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Hi Chris, :)
> The ZNAP green helicopter set (which I got three of last
> year at $9 each!)
> had some little round turbine-like parts, basically a ducted
> fan. Never tried them out to see if they're actually aerodynamically
I have that set. That was one of the first tests I did when I got it.
It's my only ZNAP set. I bought it because of the motor, the flex and those
wheel/"turbine".
From what I remember, it doesn't work that well. It's too tiny. It only
makes a little breeze.
I think it could make a water propeller though, using the flexible drive
shafts to keep the motors safe from the water. I never tried it... yet.
I'm keeping my LEGO away from the water for now. At least as long as I can
think of "dry" projects ;)
> functional, but if they were, you could put them in vertical ducts,
> driven by the ZNAP flexible drive shafts to float the skirts.
>
> Ground effect vehicles require quite a bit of power-to-weight,
Yeah, I know :( ...but at least if it could lift the "frame"+motor(s?).
With all the batts offloaded from it.
erm... <dream> If only LEGO could make some LEGO electric "turbo" air
generator like those found in micro-dust-blowers (I don't know the proper
name) and a LEGO rubber "skirt"... </dream>
> 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.
The keyword here (for now) is "powerful motor". Maybe the new RC-Buggy
motors could drive a fan fast enough for a decent air flow.
I don't own that set (yet?), so, I'll make some tests with the other two
types of motors, at home, tonight. I'll try LEGO and non-LEGO fan/blades.
mc.
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On Tue, Nov 26, 2002 at 04:44:31PM +0000, Marco Correia wrote:
> erm... <dream> If only LEGO could make some LEGO electric "turbo" air
> generator like those found in micro-dust-blowers (I don't know the proper
> name) and a LEGO rubber "skirt"... </dream>
Hi,
I'm not sure whether this would work or not but one possibility is using an
inner tube from a mountain bike tyre. They are strong, reasonably light and
look to be just the right size. Also small holes could be made on the inside of
the skirt to blow air in to the underside (as mentioned by someone else). As
for the motor/fan issue then I'm not sure but I guess model aeroplane shops
would be the best bet. Ducted fan models of fast jets are quite popular but I
think the torque required to drive one would be quite high.
Cheers,
Lee
PS The inner tube would have to be cut to make it a smaller diameter but it
should be reasonably easy to glue the two ends together.
--
--
leep@bogus.net DOC #25 GLASS #136
You can never break the chain
There is never love without pain - Secret Touch, Rush
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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?....
--
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