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Hello pneumatics fans,
I have been working a lot with pneumatics lately, and have made some
interesting discoveries. I think the most notable is a method of using the
old style red cylinders with the new pneumatics system. I came across this
as I was working on a recent robot, and I wanted to minimize the amount of
air required. There was a thread not too long ago about pneumatic check
valves, creating a vacuum, etc. When I read this post:
http://news.lugnet.com/robotics/?n=16764
It jumped out at me. C.S. Soh was saying you can't use the old single acting
cylinders with air tanks. Not true! I wanted to reply, but I didn't have any
pictures up on my site at the time, so I have waited until now. Anyway, have
a look:
http://www.ecf.utoronto.ca/~stehlik/ideas.html
On the pneumatics page, you will also see some unusual compressor designs
and a valve switching unit that controls two valves with one motor.
Eventually I would like to make Ldraw instructions for this unit, as it is
very useful and reliable. You can see an application of the single acting
cylinder here:
http://www.ecf.utoronto.ca/~stehlik/projX.html
Oh yeah, this is old news, but if you want to see an application of vacuum
tanks, see my window walker:
http://www.ecf.utoronto.ca/~stehlik/wwpics.html
Enjoy,
Rob
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Wow!! That is a fantastic model, it's a shame they're not produced
anymore - I wonder if TLG would be capable of manufacturing parts which
function the same way as the old ones did? If it were possible to obtain
new parts that performed the same function, I'd certainly have a few uses
for them. :-)
--
Cheers ...
Geoffrey Hyde
(Remove spamblock to reply.)
"Rob Stehlik" <robbby31@hotmail.com> wrote in message
news:GsB2x2.58x@lugnet.com...
> Hello pneumatics fans,
> I have been working a lot with pneumatics lately, and have made some
> interesting discoveries. I think the most notable is a method of using the
> old style red cylinders with the new pneumatics system. I came across this
> as I was working on a recent robot, and I wanted to minimize the amount of
> air required. There was a thread not too long ago about pneumatic check
> valves, creating a vacuum, etc. When I read this post:
> http://news.lugnet.com/robotics/?n=16764
> It jumped out at me. C.S. Soh was saying you can't use the old single • acting
> cylinders with air tanks. Not true! I wanted to reply, but I didn't have • any
> pictures up on my site at the time, so I have waited until now. Anyway, • have
> a look:
> http://www.ecf.utoronto.ca/~stehlik/ideas.html
> On the pneumatics page, you will also see some unusual compressor designs
> and a valve switching unit that controls two valves with one motor.
> Eventually I would like to make Ldraw instructions for this unit, as it is
> very useful and reliable. You can see an application of the single acting
> cylinder here:
> http://www.ecf.utoronto.ca/~stehlik/projX.html
> Oh yeah, this is old news, but if you want to see an application of vacuum
> tanks, see my window walker:
> http://www.ecf.utoronto.ca/~stehlik/wwpics.html
> Enjoy,
> Rob
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Hi there, Rob
That thread led to an extensive discussion into the depths of "vacuum
storage". It would appear that storing compressed air is no problem but
'the whole concept of "storing vacuum" is a little disturbing.'
Well, you can certainly pump air into a blue air tank (using the
recommended 30-35 strokes of the new hand pump) and power your pneumatic
device from off the compressed air for say 5-6 cycles before you need to
charge up the air tank again. As a matter of fact, Mario Ferrari has
used the compressed air stored in 7 of the blue air tanks to drive
"Eolo" his Sumo robot to victory.
Now try to *store* vacuum in one or more of the blue air tanks. Stop
your pump and try to work your pneumatic device from off the "stored
vacuum". How many cycles do you think your old pneumatic based device
would work before you have to regenerate the vacuum?
It is in this context that Christophe and I said that the air tank would
not work with the old style pneumatics.
I note that your window walker has an umbilical that leads to one of the
old hand pump which I figure has to be worked continuously. So you are
not really relying on stored vacuum but have to generate it
continuously. In which case an air tank to *store vacuum* would not be
needed. I wonder if the creature may work better without the air
tanks...
Cheers!
Rob Stehlik wrote:
>
> Hello pneumatics fans,
> I have been working a lot with pneumatics lately, and have made some
> interesting discoveries. I think the most notable is a method of using the
> old style red cylinders with the new pneumatics system. I came across this
> as I was working on a recent robot, and I wanted to minimize the amount of
> air required. There was a thread not too long ago about pneumatic check
> valves, creating a vacuum, etc. When I read this post:
> http://news.lugnet.com/robotics/?n=16764
> It jumped out at me. C.S. Soh was saying you can't use the old single acting
> cylinders with air tanks. Not true! I wanted to reply, but I didn't have any
> pictures up on my site at the time, so I have waited until now. Anyway, have
> a look:
> http://www.ecf.utoronto.ca/~stehlik/ideas.html
> On the pneumatics page, you will also see some unusual compressor designs
> and a valve switching unit that controls two valves with one motor.
> Eventually I would like to make Ldraw instructions for this unit, as it is
> very useful and reliable. You can see an application of the single acting
> cylinder here:
> http://www.ecf.utoronto.ca/~stehlik/projX.html
> Oh yeah, this is old news, but if you want to see an application of vacuum
> tanks, see my window walker:
> http://www.ecf.utoronto.ca/~stehlik/wwpics.html
> Enjoy,
> Rob
--
C S Soh
CSSoh's Lego Pneumatics
http://www.geocities.com/cssoh1
... where air is power!
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> Well, you can certainly pump air into a blue air tank [...]
> Now try to *store* vacuum in one or more of the blue air tanks [...]
Now things get a little philosophical :)
The air tank itself has no idea about vacuum or pressure. The only thing
the tank stores is a pressure difference. The difference between the outer
pressure and the inner presure. This difference might be positive or
negative.
In case of positive difference ("high pressure") the only limit for the
system is the point where the tubes drop from the pumps because the presure
gets too high.
In case of negative difference ("vacuum") the outer air pressure will press
the tubes (whats the english word for it? You know, the flexible things
between the pump and the valves etc...). Might be, outer pressure will in
the end bring the inner diameter of the tube to zero.
I don't have a single acting pump to experiment with vacuum, but I think
the main problem is that the technic system is developed for high pressure,
so it will be more effective on that.
It could be interesting to experiment with a stiff tube that can not be
shut by outer air pressure to increase vacuum efficiency.
Mike
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> It could be interesting to experiment with a stiff tube that can not be
> shut by outer air pressure to increase vacuum efficiency.
You cold use the "stylish" hard plastic tubing that came with a lot of
Technic sets in late '90ies and also act's as outer hose for flexi
cables.
Of course you'll still need small portions of pneumatic hoses but at
least the amount is limited.
/Tobbe
http://www.arnesson.nu/lotek/
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Hi,
Can anybody tell me what gears drive the old caterpillar tread chainlinks
(service pack 5244 I think) and at what spacing the axles would be for a
pack of 54 (I'm assuming you need two packs, one for each side)
Thanks
William
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"c s soh" <cssoh@singnet.com.sg> wrote in message
news:3C8076A2.E27D98A@singnet.com.sg...
> Hi there, Rob
>
> That thread led to an extensive discussion into the depths of "vacuum
> storage". It would appear that storing compressed air is no problem but
> 'the whole concept of "storing vacuum" is a little disturbing.'
You most certainly can store vacuum. How would a TV set work, otherwise?
When the tube is finally smashed or broken at the end of it's life, the
vacuum promptly disappears.
> Well, you can certainly pump air into a blue air tank (using the
> recommended 30-35 strokes of the new hand pump) and power your pneumatic
> device from off the compressed air for say 5-6 cycles before you need to
> charge up the air tank again. As a matter of fact, Mario Ferrari has
> used the compressed air stored in 7 of the blue air tanks to drive
> "Eolo" his Sumo robot to victory.
>
> Now try to *store* vacuum in one or more of the blue air tanks. Stop
> your pump and try to work your pneumatic device from off the "stored
> vacuum". How many cycles do you think your old pneumatic based device
> would work before you have to regenerate the vacuum?
You are confusing the stored vacuum that someone has created with the
operation of the old-style pneumatic system. Old-style pneumatics wouldn't
benefit from air tanks simply because there is no practical use for air
tanks in them - you could pressurize a piston and force it out to it's
maximum travel and have to do it with the handpump forcibly several times,
and then flip the switch the other way and watch the entire pressure
contained in the piston release itself in about 2 seconds. This was
especially true with a relatively light load on it.
> It is in this context that Christophe and I said that the air tank would
> not work with the old style pneumatics.
Because it did not rely on the concept of storing either air pressure or
vacuum, it relied on the creation of air pressure and of vacuum to take that
air pressure away.
> I note that your window walker has an umbilical that leads to one of the
> old hand pump which I figure has to be worked continuously. So you are
> not really relying on stored vacuum but have to generate it
> continuously. In which case an air tank to *store vacuum* would not be
> needed. I wonder if the creature may work better without the air
> tanks...
In conventional models, one has a need to generate air pressure
continuously, too. A vacuum has a negative pressure effect, without it if
you sucked the air out of everything the pressure of the atmosphere outside
would simply crush the object having air sucked out of it. Again, if vacuum
didn't have negative pressure where it exists, the TV wouldn't work! A note
here, the TV set does rely somewhat on the construction of glass that
comprises it's shape, but if the container you have has no physical strength
of it's own, there would be nowhere for the vacuum to be held, therefore the
vacuum is exerting negative pressure.
A vacuum could be said to be not just a space devoid of air or other matter,
it could also be said to be a physical force exerted on something that holds
it to a particular location. I wonder why they invented vacuum cleaners in
the first place, otherwise? ;-)
This is getting technical, I wonder if there's a lugnet.science or similar
discussion group? :-)
--
Cheers ...
Geoffrey Hyde
(Remove spamblock to reply.)
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Geoffrey Hyde wrote:
> ... Old-style pneumatics wouldn't
> benefit from air tanks simply because there is no practical use for air
> tanks in them
Exactly!
> > It is in this context that Christophe and I said that the air tank would
> > not work with the old style pneumatics.
>
> Because it did not rely on the concept of storing either air pressure or
> vacuum, it relied on the creation of air pressure and of vacuum to take that
> air pressure away.
That's right!
> In conventional models, one has a need to generate air pressure
> continuously, too.
Oh oh! Methinks you have not had the simple pleasure of playing with a
hand pump (the new type of course) and an air tank like in the 8250
Submarine or 8462 Tow Truck or such like. Try it!
> This is getting technical, I wonder if there's a lugnet.science or similar
> discussion group? :-)
No need, just build the model and try it out for yourself.
Nothing like the pleasure of finding things out, to quote Richard
Feynman :-)
--
C S Soh
CSSoh's Lego Pneumatics
http://www.geocities.com/cssoh1
... where air is power!
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c s soh wrote:
>
> Oh oh! Methinks you have not had the simple pleasure of playing with a
> hand pump (the new type of course) and an air tank like in the 8250
> Submarine or 8462 Tow Truck or such like. Try it!
Umm... you still need the recharge the pressure in the tank once in a
while, dont you?
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Trevyn Watson wrote:
>
> Umm... you still need the recharge the pressure in the tank once in a
> while, dont you?
But, of course. As was carefully explained in my earlier post at
http://news.lugnet.com/technic/?n=6795
Point is, you can store compressed air in a blue air tank (or as many of
them as you have in your possession) and then release it for use later
on. Then you charge it up again. Repeat as often as you like.
Try doing that with suction. Ouch, I hesitate to say *vacuum* :-)
--
C S Soh
CSSoh's Lego Pneumatics
http://www.geocities.com/cssoh1
... where air is power!
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c s soh wrote:
>
> Point is, you can store compressed air in a blue air tank (or as many of
> them as you have in your possession) and then release it for use later
> on. Then you charge it up again. Repeat as often as you like.
>
> Try doing that with suction. Ouch, I hesitate to say *vacuum* :-)
But this is exactly how Rob's window walker worked. I had the privilege
of seeing it first person, and he would work the pump a bit (to take air
out of the blue tanks), then start it going. Then after a while, he
would work the pump more. This is the same as any regular pneumatics
application (in which you build up pressure, then run for a bit, then
build up more).
I don't know if this will help or hurt my argument, but here it is:
When you use any regular pneumatics device, you are applying exactly the
same principle as the winodw walker. You are relying on the fact that
you have enough pressure in your system pushing your cylinder outwards
to counteract the air pressure pushing in the opposite direction.
I hope ive explained my point clearly :)
Trevyn.
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Trevyn Watson wrote:
>
> But this is exactly how Rob's window walker worked. I had the privilege
> of seeing it first person, and he would work the pump a bit (to take air
> out of the blue tanks), then start it going. Then after a while, he
> would work the pump more. This is the same as any regular pneumatics
> application (in which you build up pressure, then run for a bit, then
> build up more).
>
> I hope ive explained my point clearly :)
Hi, those who have the old pneumatics and a couple of the blue air tanks
may want to try the experimental setup at
http://www.geocities.com/cssoh1/primer/oldpneu.htm
Try it!
And I suspect the window walker critter would still work without the air
tanks :-)
--
C S Soh
CSSoh's Lego Pneumatics
http://www.geocities.com/cssoh1
... where air is power!
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c s soh wrote:
>
> And I suspect the window walker critter would still work without the air
> tanks :-)
Hey, don't blame me if it should fall off though ;-)
Speaking of wall climbing robots, does anyone have or seen one of these
4-legged Climb@Tron creatures shown at
http://www.neatitems.com/robots.htm
They look kinda cute especially Vertibug. And at $14.95 each, they're a
lot cheaper than one assembled from Lego.
--
C S Soh
CSSoh's Lego Pneumatics
http://www.geocities.com/cssoh1
... where air is power!
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c s soh wrote:
>
> And I suspect the window walker critter would still work without the air
> tanks :-)
And most other pneumatics systems do too, but its easier if you have a
tank in which you have a high pressure (or a low pressure).
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Hello again,
I think I should have another go at this... I wanted to say "Check
this out, I found an interesting application for the old pneumatic
cylinders" What it came out sounding like was "Mr. Soh was wrong! Look
at me prove him wrong!"
Sorry about that. That wasn't my point. Anyway, If you have a look at
the links I posted earlier, you can see how I used the old red
cylinder asd a single acting cylinder with spring return:
http://www.ecf.utoronto.ca/~stehlik/images/ideas/pneumatics/old3.jpg
This type of pneumatic cylinder is very common in industry, as it
needs only one air line, and uses half the amount of air. To do this
with Lego, the only trick was putting elastics around the piston to
provide the spring return, and plugging up the unused port on the
valve. Actually, this same thing can be done with the new cylinders,
just don't connect a hose to the top port. The old style cylinders
just offer more speed and less friction. Originally, in the old
pneumatics system the air would be pumped in to extend the piston, and
the air would be sucked out to retract it. As several people have
pointed out, the suction does not work too well to pull the cylinders
back. Correct me if I am wrong, but this type of 'suction retraction'
is not commonly used in industry. I found that spring return is much
more effective, and you don't have to bother with the suction at all.
About the vacuum tanks... I won't beat this point to death, but I have
a few thoughts. According to the laws of phsics, gas flows from a high
pressure region to a low pressure region. When you compress air into a
tank, you are essentially creating a high pressure region. The air in
the tank will be at slightly higher pressure than atmospheric, so it
want to flow out of the tank. Now, lets do the opposite thing with a
suction pump: By pumping air out of the tank, you create a low
pressure region. This is by no means a vacuum, since you can not
remove all of the air with a lego pump, but describing it as a vacuum
tank seems to make sense. Since the air outside of the tank is at
atmospheric pressure, and inside the tank is at a lower pressure, the
air want to flow into the tank. Its really just the opposite of
compressing air. Now, in both cases, the air will move only as long as
the pressure difference is maintained. So if you pump up an air tank,
you can extend and retract a cylinder a few times until the pressure
in the tank drops to atmospheric pressure. With the low pressure tank,
you can suck air into it until the pressure increases to atmospheric
pressure. So... my window walker can climb happily away as long as the
tanks have a lower than atmospheric pressure in them. If I pump most
of the air out to start, the robot can climb about 6 steps before
needing a recharge. I suppose it would work without the air tanks, but
not as well:)
Rob
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> Its really just the opposite of compressing air.
True, but there is one notable difference, as others have pointed out
before:
When compressiong air, the pressure difference is limited only by
implementation details. The pressure inside the tank usually is not just
slightly higher than outside, but multiple times the outside pressure.
When removing air from the tank, the theoretical limit for pressure
difference between inside and outside is the atmospheric pressure itself.
And real implementations in the price range we are talking don't even get
near that, so the amount of energy you can store by sucking air out of an
air tank is very limited.
> If I pump most
> of the air out to start, the robot can climb about 6 steps before
> needing a recharge. I suppose it would work without the air tanks, but
> not as well:)
I suppose it would work even better if you could figure a way to use
pressure instead of vacuum. But that may not be feasible ...
Greetings
Horst
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Rob Stehlik wrote:
>
> Hello again,
> I think I should have another go at this... I wanted to say "Check
> this out, I found an interesting application for the old pneumatic
> cylinders" What it came out sounding like was "Mr. Soh was wrong! Look
> at me prove him wrong!"
How coincidental, but it too struck me that we needed to backtrack as
the thread was getting pretty muddled up. It seemed to me that we may
not be working on the same assumptions. So here's the re-play...
The post that you quoted http://news.lugnet.com/robotics/?n=16764
was in response to Jennifer Clark's suggestion to use two air tanks, one
on the high pressure hose and the other on the vacuum hose between the
pneumatic diode and the valve.
The tacit assumption here is that the pneumatics were being used in the
conventional manner, that is with pneumatic cylinders being controlled
by the valve to retract and to extend the piston. It is in this context
that it was said that the air tanks would not work with the old
pneumatics. (The experimental setup is shown at
http://www.geocities.com/cssoh1/primer/oldpneu.htm).
But perhaps, it would have been clearer if I had qualified that the air
tanks would not work with the old pneumatics *when connected in the
conventional manner* (hopefully this is easily understood).
> ... my window walker can climb happily away as long as the
> tanks have a lower than atmospheric pressure in them. If I pump most
> of the air out to start, the robot can climb about 6 steps before
> needing a recharge. I suppose it would work without the air tanks, but
> not as well:)
Now, the window walker is an exception. It is not using the old
pneumatics in the conventional manner (as defined above). Indeed, it is
using pneumatics in a most irregular manner. There are none of the old
pneumatic cylinders to speak of. Therefore there is no need for
alternate compression and suction. The pneumatic valve is simply being
used to switch the *vacuum* from one pair of suction cups to the other
pair. So I reckon this critter can be left to continue carrying the
tanks on its back ;-)
--
C S Soh
CSSoh's Lego Pneumatics
http://www.geocities.com/cssoh1
... where air is power!
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Very nice design. I don't have access to old style pneumatic cylinders, but
was thinking of doing something similar with the new double acting
cylinders. Because I don't have a check valve in the new pneumatics that
would allow me to store vacuum, I would have to change the design a bit though.
My idea was to use suction cups as you did. The suction cups would be
attached via a hose to the bottom (retract) side of one of the new large
cylinders. To generate suction my contraption would lightly press the cup
against the glass, and then extend the cylinder. I am thinking that I would
need one cylinder per suction cup. This is based (very) roughly on your
statement about getting 6 steps from one charge of the two air tanks.
What do you think? Does it sound feasable at all? And how did you attach
your suction cups to the LEGO?
Any and all suggestions are appreciated.
Dean
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