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Ok, so we have the 4, 3 and 2 (LegWay :) wheel bots...
and the 8, 6, 3, 2, 1(?) leg BOTs.
...but, what about a 0 (zero) Wheel / Leg Bot ?
Ok, there's the pseudo-flying bots :)) but, apart from some trials with
blimps (helium balloons?) and pseudo-Helicopters and drawings for
delta-wings solutions... is there a Hovercraft-type solution ?
Questions:
1) Has anyone done / tried this ?
2) Is there a LEGO-only solution to this ?
(the "rubber" around to trap the air flow underneath doesn't count.)
Even if all the Batteries and/or the controlling unit (be it an RCX or the
radio receiver from RC Buggy) not onboard.
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 :)
mc.
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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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Marco Correia wrote:
> 3) Is there a LEGO-only way to generate enough air flow (pressure) ?
The experiments we've done with the helicopter suggest that you can
generate some pretty impressive volumes of fairly slow moving air -
but high speed/low volume is hard.
The RDS insect wings that we used on our helicopter work really well,
but I don't think they'd be much use for a helicopter unless you had
a funnel to take the large volume low speed air and speed it up into
a narrow stream that could inflate a hovercraft's skirt.
I've seen toy hovercraft that worked well with very small motors.
> 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.
Hmmm - interesting.
---------------------------- 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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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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A ducted fan approach may work.
Ducted fan hovercraft have one or two big fan blades on the back that push
the craft forward, but a duct takes some of the air and uses it to fill the
skirt. This is probably the "lightest" design approach. Direction
(including reverse) is controlled by vanes on the very back.
There is also the famous British hovercraft that had a HUGE thrust fan in
the center of it. The duct looks similar to those nuclear plant tower
hourglass shapes. Although, this design (in LEGO) would be very heavy and
the thrust probably wouldn't be enough.
In either case, one might consider using a thin baseplates for the deck.
- Rob
----- Original Message -----
From: "Steve Baker" <sjbaker1@airmail.net>
To: <marco@soporcel.pt>
Cc: <lego-robotics@crynwr.com>
Sent: Tuesday, November 26, 2002 5:00 PM
Subject: Re: "real" LEGO Hovercraft ? (with/without batteries/RCX "onboard")
> Marco Correia wrote:
>
> > 3) Is there a LEGO-only way to generate enough air flow (pressure) ?
>
> The experiments we've done with the helicopter suggest that you can
> generate some pretty impressive volumes of fairly slow moving air -
> but high speed/low volume is hard.
>
> The RDS insect wings that we used on our helicopter work really well,
> but I don't think they'd be much use for a helicopter unless you had
> a funnel to take the large volume low speed air and speed it up into
> a narrow stream that could inflate a hovercraft's skirt.
>
> I've seen toy hovercraft that worked well with very small motors.
>
> > 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.
>
> Hmmm - interesting.
>
> ---------------------------- 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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On Tue, 26 Nov 2002, Rob Limbaugh wrote:
> A ducted fan approach may work.
>
> Ducted fan hovercraft have one or two big fan blades on the back that push
> the craft forward, but a duct takes some of the air and uses it to fill the
> skirt. This is probably the "lightest" design approach. Direction
> (including reverse) is controlled by vanes on the very back.
Basic LCAC design. The air that drives the skirt is -not- derived from the
direction fans but rather from the turbine input plenums (those babies
will suck as much air in just a few 10's of sec. as goes through your
entire house in year). If you took air from the vector fans you wouldn't
be able to fill the skirt until -after- you started to move, which
requires the skirt to be filled. And reverse is -not- derived from vanes,
but rather a PTO with a reverse gear, turbines only turn one way. Most
LCAC's -won't- go backward, they rotate around their 'center of thrust'
(as compared to center of gravity), which does use the vanes.
The ones that -used- to ply the English Channel were always favorites of
mine. It's a pity I'll never get to ride one now.
--
____________________________________________________________________
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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On Tue, 26 Nov 2002, Steve Baker wrote:
> That was the SRN1 - the worlds first working full-sized
> hovercraft - which (amazingly) didn't have a skirt.
Several of the original hovercraft didn't have skirts, they were the
running board sitting on the ground.
There is a simple childrens science experiment to demonstrate the effect.
Take a sewing thread spool (the old wood kind work best) and put a straw
down the middle. Then blow down the straw, the spool will float.
--
____________________________________________________________________
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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Hi Rob :)
> A ducted fan approach may work.
Yes, I *think* that's the only way.
> There is also the famous British hovercraft that had a HUGE
> thrust fan in the center of it.
That's my first approach. I'll deal with motion next.
> The duct looks similar to those nuclear plant tower
> hourglass shapes. Although, this design (in LEGO) would be
> very heavy and the thrust probably wouldn't be enough.
100% LEGO yes, but I'm planning on using LEGO (maybe ZNAP at first, then a
mix of Technic) as the "wire-frame" and then use plastic film to "fill" the
all thing.
mc.
PS: A cool thing would be if LEGO became interested in this, and could build
custom light ducted propellers and/or an electric ducted air turbine...
erm... and then release it as another Mindstorms Expansion or as a complete
(working) Hovercraft Technic set ;)
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In lugnet.robotics, Marco Correia writes:
> Ok, there's the pseudo-flying bots :)) but, apart from some trials with
> blimps (helium balloons?) and pseudo-Helicopters and drawings for
> delta-wings solutions... is there a Hovercraft-type solution ?
>
> Questions:
>
> 1) Has anyone done / tried this ?
http://www.ucl.ac.uk/~uczxhpf/
This is a nice project, they built a human-powered hovercraft that was
just able to lift a person from the ground. I read a dutch article
on it, they also refer to a few books on hovercraft design.
> 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.
The project above uses styrofoam to make the unit as light as possible.
Combining these lighter materials with lego might be a solution.
Mark-Jan
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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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Hi Dan,
> There was an excellent episode of JunkYard Wars where they
> demonstrated just how easy, relatively speaking, it is to build a
> hovercraft.
>
> http://tlc.discovery.com/fansites/junkyard/episode/season_042.html
Yeah =) I saw it too !
> Now piloting it once it's built, there's the tricky part...
ok, I think that now everyone knows that I like hovercrafts... never had
one... but then, I always liked helicopters and never had one also.
hmmm... I just remembered I have a cpu cooling fan laying around... maybe...
well, it's becoming less and less a LEGOish, but, won't hurt trying it also.
mc.
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While doing my initial searches to check if this could be done, I found
this:
http://www.lego.com/build/features/mbuilder/madsen/default.asp
Take a look at this:
"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-AT™, 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)."
WOW! "a Hovercraft that really flies!" YEAH! ...now, if only LEGO could
release it as a set ;) ...or more realistically (price), as an "add-on"
kit/pack with only the custom parts necessary to do it (a bit like the
pneumatic pack or mindstorms expansion kit)
Hans Madsen could at least release some photos, specs or describe what kind
of "cheats" he used so it could "fly".
mc. :)
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no! cpu fan doesn't work in this aplication even if you increase voltage 2
times
pixel
"Marco Correia" <lego-robotics@crynwr.com> wrote in message
news:000a01c2963b$e3ede210$610b010a@soporcel.pt...
> Hi Dan,
>
> > There was an excellent episode of JunkYard Wars where they
> > demonstrated just how easy, relatively speaking, it is to build a
> > hovercraft.
> >
> > http://tlc.discovery.com/fansites/junkyard/episode/season_042.html
>
> Yeah =) I saw it too !
>
> > Now piloting it once it's built, there's the tricky part...
>
> ok, I think that now everyone knows that I like hovercrafts... never had
> one... but then, I always liked helicopters and never had one also.
>
> hmmm... I just remembered I have a cpu cooling fan laying around... • maybe...
> well, it's becoming less and less a LEGOish, but, won't hurt trying it • also.
>
> mc.
>
>
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pixel wrote
> Marco wrote
> > hmmm... I just remembered I have a cpu cooling fan laying around...
> > maybe...
> no! cpu fan doesn't work in this aplication even if you
> increase voltage 2
> times
yup, I confirmed that yesterday :/
though now I have a nice ZNAP micro ventilator, for the hot summer, ehehe
now... let's see what happens tonight, with the 9v ungeared LEGO motor and a
non-LEGO propeller together with an "air trap".
mc.
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if i will use non lego or znap propeler will you disqualificate me? :)
be cause IMO some kind of turbine is needed here
i'll try to do it tonight
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pixel wrote:
> if i will use non lego or znap propeler will you disqualificate me? :)
LOL! No ! I myself am doing tests with a non-LEGO one also.
it would be nice if it could use a LEGO motor... and material usually found
in every home, so anyone could build one... if we ever find a way to make it
possible.
> because IMO some kind of turbine is needed here
Yep. Do you have any clever trick to do it ?
(besides using a turbine from a hovercraft kit ;)
> i'll try to do it tonight
good ! the more trying the better :)
mc.
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hi!
so i did tests
and my discoveries are sad
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
2. lego motor http://peeron.com/inv/parts/2838c01 is the only one useful
because the new motor has no enough speed
3. propeler has to be non-lego beacause of weight and shape and stability
4. turbine can be weighty so motor can rotate it and keep the speed
(flywheel)
5. good turbine is cd-disc :)) cut on chords and bent termicaly (it's heavy
enough) (you need some tools to do it)
6. for me it's impossible to do lego frame light enough (in fact lego parts
are heavy especialy axles)
7. making skirt is very important (i did it from plastic bag) it's a little
bit hard to do it
so this is 7 sad observations
now i'm not really suprised to hear taht even small planes has very big and
powerfull engines
(those ones which haven't big engine have big wings)
but i'll keep trying
and i hope all of you guys too
br
pixel
"Marco Correia" <marco@soporcel.pt> wrote in message
news:004201c296f9$fe447e80$610b010a@soporcel.pt...
> pixel wrote:
> > if i will use non lego or znap propeler will you disqualificate me? :)
>
> LOL! No ! I myself am doing tests with a non-LEGO one also.
>
> it would be nice if it could use a LEGO motor... and material usually • found
> in every home, so anyone could build one... if we ever find a way to make • it
> possible.
>
> > because IMO some kind of turbine is needed here
>
> Yep. Do you have any clever trick to do it ?
> (besides using a turbine from a hovercraft kit ;)
>
> > i'll try to do it tonight
>
> good ! the more trying the better :)
>
> mc.
>
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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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