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On Fri, 29 Nov 2002, pixel wrote:
> 1. pure turbine has to be placed in some kind of tunnel but not exactly
> funnel
> the tunnel has to be as a part of ball (sphere) without hats :)) at the
> upper and the lower side
> because the stream of air has to compact and air cannot escape near the
> blade of rotor or turbine
Bingo.
> 2. lego motor http://peeron.com/inv/parts/2838c01 is the only one useful
> because the new motor has no enough speed
Take a look at some of these micro motors that are being used in the new
mini-RC cars. You can buy a whole car kit, radio, and controller for about
$75US.
> 3. propeler has to be non-lego beacause of weight and shape and stability
A helo tail rotor is your best bet. Wood or a composite is your best bet.
Stay away from -any- metal blades as they are a serious safety hazard in
this application.
> 4. turbine can be weighty so motor can rotate it and keep the speed
> (flywheel)
No, you don't need a turbine. What you're missing is the ratio of the
inlet area to exhaust plenum area and the delta-v of the air flow.
200lb's will get a good lift from 1/4hp.
200lb's weight of hover
------- = ---------------
1/4hp power of motor
> 5. good turbine is cd-disc :)) cut on chords and bent termicaly (it's heavy
> enough) (you need some tools to do it)
Yuck. A CD disk is -way- too big across, and it's aerodynamic efficiency
is insufficient to move enough air. At high air speeds the flat 'blades'
will stall and you will find the flow going down with increases in fan
speed. Your fan shouldn't be more than about 4 inches across.
> 6. for me it's impossible to do lego frame light enough (in fact lego parts
> are heavy especialy axles)
I suspect this isn't true. I'd start with a standard green plate and
eschew the whole idea of a frame, insufficient rigidity in Lego plastic.
> 7. making skirt is very important (i did it from plastic bag) it's a little
> bit hard to do it
Shouldn't be. I'd suspect it's your process, remember you -must- pleat the
corners or the skirt will dump. Hint, the pleats -must- be vertical with
respect to the running board/ground reference frame.
If you're making a tubular skirt then you want to make it in eight (8)
seperate sections. Four (4) straight tubular pieces, use a wood dowel
or a similar form to make. Then the four (4) corner pieces.
--
____________________________________________________________________
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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but wher is the fun?
my skirt has been done as a cut of the sphere
the same shapa as the tunnel has to hav (i think)
so it was a middle part of sphere without upper and lower domes
that's why i said "a little bit hard to do it" :))
you said CD is too big
?
CD has 5 1/4 inch so it's not much bigger than you said - 4 inches
but i suppose you are right!
have a look here
http://web.mit.edu/sp.742/www/motor.html
i must check the weight of lego-motors to use your formulas
but they are useful - thanx
i've been trying 12V
and read somewhere that 18V quadruple torque!
so:
aprox:
0.37W * 4 = 1.5W
and 1hp = ca 750W
so lego motor has 0.002 hp
so
we can lift ca 0.3lb
so i think lego motor cannot lift itself
so end of topic isn't it?
the answer is: you stole whole fun from this issue :((((
and now - me too :(((((((((((((
:)
best regards
pixel
"Jim Choate" <lego-robotics@crynwr.com> wrote in message
news:Pine.LNX.4.33.0211290805310.1275-100000@einstein.ssz.com...
> On Fri, 29 Nov 2002, pixel wrote:
>
> > 1. pure turbine has to be placed in some kind of tunnel but not exactly
> > funnel
> > the tunnel has to be as a part of ball (sphere) without hats :)) at • the
> > upper and the lower side
> > because the stream of air has to compact and air cannot escape near • the
> > blade of rotor or turbine
>
> Bingo.
>
> > 2. lego motor http://peeron.com/inv/parts/2838c01 is the only one useful
> > because the new motor has no enough speed
>
> Take a look at some of these micro motors that are being used in the new
> mini-RC cars. You can buy a whole car kit, radio, and controller for about
> $75US.
>
> > 3. propeler has to be non-lego beacause of weight and shape and • stability
>
> A helo tail rotor is your best bet. Wood or a composite is your best bet.
> Stay away from -any- metal blades as they are a serious safety hazard in
> this application.
>
> > 4. turbine can be weighty so motor can rotate it and keep the speed
> > (flywheel)
>
> No, you don't need a turbine. What you're missing is the ratio of the
> inlet area to exhaust plenum area and the delta-v of the air flow.
>
> 200lb's will get a good lift from 1/4hp.
>
> 200lb's weight of hover
> ------- = ---------------
> 1/4hp power of motor
>
> > 5. good turbine is cd-disc :)) cut on chords and bent termicaly (it's • heavy
> > enough) (you need some tools to do it)
>
> Yuck. A CD disk is -way- too big across, and it's aerodynamic efficiency
> is insufficient to move enough air. At high air speeds the flat 'blades'
> will stall and you will find the flow going down with increases in fan
> speed. Your fan shouldn't be more than about 4 inches across.
>
> > 6. for me it's impossible to do lego frame light enough (in fact lego • parts
> > are heavy especialy axles)
>
> I suspect this isn't true. I'd start with a standard green plate and
> eschew the whole idea of a frame, insufficient rigidity in Lego plastic.
>
> > 7. making skirt is very important (i did it from plastic bag) it's a • little
> > bit hard to do it
>
> Shouldn't be. I'd suspect it's your process, remember you -must- pleat the
> corners or the skirt will dump. Hint, the pleats -must- be vertical with
> respect to the running board/ground reference frame.
>
> If you're making a tubular skirt then you want to make it in eight (8)
> seperate sections. Four (4) straight tubular pieces, use a wood dowel
> or a similar form to make. Then the four (4) corner pieces.
>
>
> --
> ____________________________________________________________________
>
> 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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Jim Choate wrote:
> Take a look at some of these micro motors that are being used in the new
> mini-RC cars. You can buy a whole car kit, radio, and controller for about
> $75US.
The micro cars (the ones about an inch long) are down to $30 -
including two channel RC and battery charger.
However, the motors aren't all that powerful.
I read somewhere that the motors they are using are from the
'vibrators' inside pagers and cellphones. I can't imagine those
being very powerful. Their main design goal was small size and low
battery consumption.
---------------------------- 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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pixel wrote:
> but wher is the fun?
Non-lego motor -- for lower weight and higher RPM.
Non-lego skirt -- because there isn't anything in Lego
that can do that.
Non-lego propellor -- because the Lego ones are crap
Non-lego decking -- for lightness and rigidity.
...hmmm it's looking a lot like a no-Lego solution!
We all know that electric hovercraft are possible - there
are a couple of R/C hovercraft at my local toy store. Building
one from scratch would be easy...however, the challenge here is
to build one out of Lego...either 'pure' Lego or 'mostly-pure'.
> you said CD is too big
> ?
> CD has 5 1/4 inch so it's not much bigger than you said - 4 inches
> but i suppose you are right!
Remember, the area goes up as the square of the radius. Going from
a 4" radius propellor to a 5.25" CD increases the AREA swept out
by the propellor by a factor of 1.72 - so your CD is not just a little
bigger - it's 72% larger!
I don't see the reason to restrict ourselves to 4" propellors
though. What's the logic behind that?
Presuming you have appropriate duct-work, a larger prop spun
at the same speed as a smaller prop will generate more air flow -
and that's what we need here.
If our motors have poor RPM but high torque (as is certainly
the case with the geared Mindstorms motor) then a larger propellor
makes a lot of sense...it's just like changing the gear ratio's
driving it - but without the frictional losses in the gears train.
Sure there are complicated problems of losses in the propellor
design - but I suspect the size of the prop is a small factor
compared to the poor aerodynamic efficiency of any 'toy'
propellor we might pick up.
> have a look here
> http://web.mit.edu/sp.742/www/motor.html
...whoever maintains that page needs to play with the newer
geared Mindstorms motor and do an update!
> i must check the weight of lego-motors to use your formulas
> but they are useful - thanx
>
> i've been trying 12V
> and read somewhere that 18V quadruple torque!
> so:
> aprox:
> 0.37W * 4 = 1.5W
> and 1hp = ca 750W
> so lego motor has 0.002 hp
> so
> we can lift ca 0.3lb
> so i think lego motor cannot lift itself
> so end of topic isn't it?
That's not true.
It takes ZERO energy to support something against gravity.
My chair is supporting my (not inconsiderable) weight using
no energy at all.
So, supporting the weight of the hovercraft on an air cushion
doesn't necessarily have to consume more energy than the lego
motor can provide.
If you sealed up the bottom of the skirt so it was like a
balloon with no holes in it, the air pressure would support
a LOT of weight with no energy expenditure at all.
The motor is *ONLY* keeping the pressure topped-up because of
the air leaking out around the bottom of the skirt.
That's the difference between a hovercraft and a helicopter.
I'm quite prepared to say that a pure lego helicopter that can
fly freely (no counter-weights!) is impossible. But I wouldn't
rule out the possibility of a pure lego hovercraft.
---------------------------- 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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In lugnet.robotics, Steve Baker <sjbaker1@airmail.net> writes:
> Jim Choate wrote:
>
> > Take a look at some of these micro motors that are being used in the new
> > mini-RC cars. You can buy a whole car kit, radio, and controller for about
> > $75US.
>
> The micro cars (the ones about an inch long) are down to $30 -
> including two channel RC and battery charger.
>
> However, the motors aren't all that powerful.
>
> I read somewhere that the motors they are using are from the
> 'vibrators' inside pagers and cellphones. I can't imagine those
> being very powerful. Their main design goal was small size and low
> battery consumption.
>
> ---------------------------- 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
After reading thru most of this thread, and trying to work out in my mind as
to how to do it...
After work I'm going home and rip apart my modified 8448, take the 8475
motors out of it, and throw on a znap prop on those motors and see what the
air flow's like.
Putting my current project on hold, I'll try and whip something together.
If it doesn't work, oh well. I am curious though, after reading these many
good ideas.
The only thing I have to formulate in my mind is how to get an enclosure
around the znap prop so that air doesn't escape up around it.
I'll see what transpires tonite!
Dave K
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> From: Steve Baker
> I'm quite prepared to say that a pure lego helicopter that can
> fly freely (no counter-weights!) is impossible. But I wouldn't
> rule out the possibility of a pure lego hovercraft.
When I was about to give up, after some tests with a non-LEGO propeller and
*without* a "skirt", I saw this interview of LEGO Master Builder Hans Madsen
(http://www.lego.com/build/features/mbuilder/madsen/default.asp) where he
says he made one (I assume) *LEGO* "Hovercraft that really flies":
"What is the coolest model you have ever built?
Apart from the destroyer I mentioned above, I think that the coolest models
I have made are the AT-ATT, a Super Car #8448 with an RCX inside, and a
Hovercraft that really flies! Also, some of the other models from the Dark
Side Developer Kit (#9754)."
If only we could see some photos or specs of it...
mc.
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Hi Dave :)
> After reading thru most of this thread, and trying to work
> out in my mind as to how to do it...
Cool :)
> The only thing I have to formulate in my mind is how to get
> an enclosure
> around the znap prop so that air doesn't escape up around it.
I'm thinking of a thin "plastic film" usually used to wrap around food to
keep it fresh and air tight (I don't know how's it called in english).
mc.
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On Fri, 29 Nov 2002, pixel wrote:
> but wher is the fun?
You'll have to answer that for yourself. A lot of what I find fun would
probably bore/scare most to death. For example, I find all these
transformers and such that a lot of Mindstorm folks rave over completely
and utterly uninteresting, and I'm a major Transformers (c) freak. If you
like 'em, rage on. I also find the Brick to be a toy (Styx-on-a-Brick
being the major exception) and not worth the effort to mess with, though
the Lego pieces themselves are great!
> my skirt has been done as a cut of the sphere
> the same shapa as the tunnel has to hav (i think)
> so it was a middle part of sphere without upper and lower domes
> that's why i said "a little bit hard to do it" :))
Last time I checked a sphere didn't have a 'middle' per se. The piece
you're talking about is a rubber sheet toroid. Also, there is a specific
term for the 'upper and lower domes'...;)
> you said CD is too big ?
> CD has 5 1/4 inch so it's not much bigger than you said - 4 inches
> but i suppose you are right!
That extra inch is a problem (pi*r^2), a 5in circle is a -lot- bigger
than a 4in circle. A similar problem a lot of folks have is e=m*v^2.
In general they spend way(!!!) too much time playing with m when they
should be looking for improvements in v since it grows much faster (Hint).
The show stopper for using a CD is that it has zero aerodynamics. Flat
plates don't move air well, most especially at high speed (there's that v
again...).
> i must check the weight of lego-motors to use your formulas
> but they are useful - thanx
NO...the 'mass' of the hovercraft is what you want compared to the torque
of the motor coupled with the efficiency of the air handling.
Force over area is what you need to pay attention to.
Also, they're not my formula. They come straight out of any physics book.
> i've been trying 12V
> and read somewhere that 18V quadruple torque!
That would depend on the motor design I suspect.
> so:
> aprox:
> 0.37W * 4 = 1.5W
> and 1hp = ca 750W
> so lego motor has 0.002 hp
> so
> we can lift ca 0.3lb
> so i think lego motor cannot lift itself
> so end of topic isn't it?
A simple experiment with levers and pullies....you forgot
time. Horsepower is a -time dependent- quantity. I can say that you can
build a rope climber with Lego (and that requires a motor to lift it's own
weight and then some).
> the answer is: you stole whole fun from this issue :((((
> and now - me too :(((((((((((((
-You- asked, be carefull for what you ask. You might get it. I can't
help it if hovercraft are a major interest of mine (check out the roll in
the new James Bond movie, I think that is a first).
--
____________________________________________________________________
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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In lugnet.robotics, Marco Correia writes:
> Hi Dave :)
>
> > After reading thru most of this thread, and trying to work
> > out in my mind as to how to do it...
>
> Cool :)
>
> > The only thing I have to formulate in my mind is how to get
> > an enclosure
> > around the znap prop so that air doesn't escape up around it.
>
> I'm thinking of a thin "plastic film" usually used to wrap around food to
> keep it fresh and air tight (I don't know how's it called in english).
>
> mc.
I was thinking of more a complete LEGO solution--the only thing non-LEGO in
my plans is the skirt, which probably will be a bicycle innertube.
What I plan first is to get hte motor, the fan and turn it on and see if I
can dry my hair with it ;)
Secondly, set up a platform, possibly 4 32 x 32 baseplates, with 6x8 plates
joining them together at the edges, hopefully leaving a 6x6 hole right in
the middle where I'll mount the prop and motor and see if it can get enuf
air blown under the plates to at least move across a vinyl floor if pushed.
At least that's as far as I got in my head right now.
Maybe the castle arches have the same diameter as the Znap fan--we shall see.
Dave K
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On Fri, 29 Nov 2002, Steve Baker wrote:
> The micro cars (the ones about an inch long) are down to $30 -
> including two channel RC and battery charger.
>
> However, the motors aren't all that powerful.
>
> I read somewhere that the motors they are using are from the
> 'vibrators' inside pagers and cellphones. I can't imagine those
> being very powerful. Their main design goal was small size and low
> battery consumption.
We aren't interested in power, we're interested in moving a volume of air.
They are very fast, high rpm. Trade off rpm with suitable gearing. You may
need two or more (which is why small may be better).
I've never used them myself except for nervous network sorts of stuff. It
was meant as a suggestion.
If they don't work you've still got a nifty little toy car to drive around
;)
--
____________________________________________________________________
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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Marco Correia wrote:
> When I was about to give up, after some tests with a non-LEGO propeller and
> *without* a "skirt", I saw this interview of LEGO Master Builder Hans Madsen
> (http://www.lego.com/build/features/mbuilder/madsen/default.asp) where he
> says he made one (I assume) *LEGO* "Hovercraft that really flies":
So is Hans Madsen on this list?
I'm always skeptical of things that are just throwaway lines like
that...was this pure lego? How much cheating was involved?
There was a couple of photos of a lego helocopter that could
really fly on the list a few days ago...I don't think anyone
truly believes that it wasn't faked in some way.
You need proof - still photo's of the mechanisms taken up close.
Just like any scientific claim, it's not gonna be believed until
someone can reproduce it - and "Extraordinary claims require
extraordinary proof".
> If only we could see some photos or specs of it...
Yes - exactly.
---------------------------- 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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"Jim Choate" <lego-robotics@crynwr.com> wrote in message
news:Pine.LNX.4.33.0211291016430.1095-100000@einstein.ssz.com...
> On Fri, 29 Nov 2002, pixel wrote:
>
> > but wher is the fun?
>
> You'll have to answer that for yourself. A lot of what I find fun would
> probably bore/scare most to death... <cut>
no comments
man! i've been asking rhetotical :))))
i've got fun experimenting even if i know they lead to nowhere
> > my skirt has been done as a cut of the sphere
> > the same shapa as the tunnel has to hav (i think)
> > so it was a middle part of sphere without upper and lower domes
> > that's why i said "a little bit hard to do it" :))
>
> Last time I checked a sphere didn't have a 'middle' per se. The piece
> you're talking about is a rubber sheet toroid. Also, there is a specific
> term for the 'upper and lower domes'...;)
what is with your sense of humor
you have really sharp tongue :)))
that's ok but i thought we are playing here
this is not a real school :))
i like your comments...
> The show stopper for using a CD is that it has zero aerodynamics. Flat
> plates don't move air well, most especially at high speed (there's that v
> again...).
in my former posts i said that the cd has to have cuts leading by chords and
has to be bent
> Also, they're not my formula. They come straight out of any physics book.
yeah i know that
i have them in my books too but as i said
the fun (for me) is discovering america again
>
> > i've been trying 12V
> > and read somewhere that 18V quadruple torque!
>
> That would depend on the motor design I suspect.
yes but it ussually works
> > the answer is: you stole whole fun from this issue :((((
> > and now - me too :(((((((((((((
>
> -You- asked, be carefull for what you ask. You might get it.
that is really good answer :)
but my dear adversary :)
look at my next post on this group
everything wiil be clear
best regards Jim
and all
paul pixel kleniewski
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