Subject:
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Re: Pneumatics Vs. Hydraulics
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 28 Jul 2004 05:28:11 GMT
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Original-From:
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Mr S <szinn_the1@+Spamcake+yahoo.com>
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Viewed:
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1015 times
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I don't think that pressure shares the same fluid
dynamics as liquids. Certainly on the larger scale,
fluid works much better at evenly distributing
pressure even though pnuematic systems are capable of
very strong movements indeed. The viscosity of
hydraulic fluid is such that it does not compress well
where air does compress. Even on a smaller scale, the
air must compress a certain amount before it fluidly
distributes pressures, and that is the reason that
LEGO has the air tanks. The more stored pressure that
you have in the form of compressed air, the more work
you can do with the LEGO pnuematics. Fine adjustments
are capable with hydraulic systems and pnuematic
systems are used generally in open or closed
situations. If you have a need to have the valve half
open, hydraulics is your best bet. There is the
differences in a nutshell.
It is not possible to build hydraulic systems on the
scale of LEGO for the cost of LEGO. Some modelling
enthusiasts do have small scale hydraulic systems, but
they are NOT cheap.
BTW, you can make your own air tanks. The air tank in
the LEGO pnuematic systems with the two port actuators
is really only there to supply stored pressure. With a
12 or 20 ounce plastic soda bottle and some silicon
sealer, you can make a huge air tank. This makes it
possible to build a LEGO pnuematic machine which has
the capacity to do all the work needed before
recharging the tank, depending on how much work is
required, of course.
Hydraulic systems make use of a principle of physics
where a cylinder with a 1 inch square plate on one end
and a 10 inch square plate on the other, takes 10 psi
on the one inch side, and applies 10 psi to each of
the 10 square inches on the other end, thus giving a
power boost by a factor of 10. This is idealized, but
close to accurate, and the reason that hydraulic fluid
is such that it does not compress. Any compression of
the 'power transfer fluid' and the boost ratio is
decreased accordingly.
Because of the inherent leakage in the LEGO or any
pnuematic system, it requires not only air under
pressure, but large volumes of it, replenished often
or continuously, while a hydraulic system is a closed
system that requires replenishment only rarely.
Okay, see what the Captain can do?
The answer is that LEGO does NOT make hydraulic parts.
Cheers
--- Steve Baker <sjbaker1@airmail.net> wrote:
> Bruce Boyes wrote:
>
> > Does anyone make scale models which use real • hydraulics (water or mineral
> > oil maybe?). I guess water or oil leaks would be a • lot messier than air
> > leaks and the pressures might be higher too, • preventing use of
> > push-together plastic hoses.
>
> I wonder whether the viscosity of fluids scale
> reasonably? It's easy to
> imagine that the losses involved in forcing
> hydraulic oil through a tube
> with only one or two millimeter cross-sections would
> be huge compared to
> the real-world device.
>
> I suspect that pneumatics at Lego scale would
> operate more nearly like
> hydraulics at 'real world' scales.
>
> ---------------------------- Steve Baker
> -------------------------
> HomeEmail: <sjbaker1@airmail.net> WorkEmail:
> <sjbaker@link.com>
> HomePage : http://www.sjbaker.org
> Projects : http://plib.sf.net
> http://tuxaqfh.sf.net
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> http://prettypoly.sf.net
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>
>
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Message has 1 Reply:
 | | Re: Pneumatics Vs. Hydraulics
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| Some of this is not right, some is not very clear. I've been working in fluid valve design for 14 years. Let me clarify a couple things. (...) First, some definitions. Pressure is a force, fluid is a type of medium, and liquid is a type of fluid. To (...) (20 years ago, 29-Jul-04, to lugnet.robotics)
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Message is in Reply To:
| | Re: Pneumatics Vs. Hydraulics
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| (...) I wonder whether the viscosity of fluids scale reasonably? It's easy to imagine that the losses involved in forcing hydraulic oil through a tube with only one or two millimeter cross-sections would be huge compared to the real-world device. I (...) (20 years ago, 28-Jul-04, to lugnet.robotics)
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