Subject:
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putting liquid into pneumatic elements (was Re: Darn those definitions (was: The new Super Car)
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 10 Aug 1999 21:17:37 GMT
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Viewed:
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916 times
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In lugnet.robotics, lego-robotics@crynwr.com (Jacob Schultz) writes:
> What will actually happen, if you fill water into the LEGO pneumatic parts?
> Will they still work? And will they become hydrolics?
The pneumatic compression cylinders, also called "pumps" are not
airtight, and they wouldn't be watertight if filled with water. When
you push on them they would apply pressure to the water all right, but
when you pull on them they would simply let air into the system.
Also, it would be really hard to get the water into the system in the first
place. The most difficult problem in getting water into the pneumatic elements
is that there are no bleed valves, so you effectively have to assemble the
entire circuit under water, run the pumps, hold elements upside down so air can
escape, etc. I suppose it's also possible they might get damaged somehow if
they got wet inside. Probably not, because LEGO probably thought of that. After
all, kids are going to build 8250 Search Sub and then they'll try to use it
underwater. I would if I was a kid.
More importantly to your question however, is that the resulting "hydraulic"
system wouldn't be too useful. One of the primary advantages of pneumatics is
the ability to store energy in the air tank, and that advantage is lost in a
liquid-based system. It's not practical to try to store energy in a tank of
water via the pressure of the water in the tank and then extract that energy by
letting the water expand. Its compressibility is too low. (See
http://www.lugnet.com/off-topic/geek/?n=381 if you want to know just how low!)
Hydraulics also have the advantage that they transmit high pressure directly;
there's no "squishiness" or "springiness" to it like there is with air. That
means you can press hard and (almost) all the energy goes to doing useful work,
rather than a lot of it getting absorbed by compressing the gas. But, you can
remove much of the "springiness" in a pneumatic system by removing the air
tank. Then the total volume of the circuit is only a little more than the
volume of the two cylinders (the pump and the "output" cylinder).
I suppose you could connect two pneumatic "output" cylinders to each other and
get a good approximation of a hydraulic circuit. But I think it would still
leak a little, the weak point being the piston-ring seal inside the two
cylinders. You could also make a reasonably good air-powered water gun. Boy,
now there's a good weapon for robot wars. Disable your opponent by shorting out
its RCX! {=8 <- evil grin
- Robert Munafo
LEGO: TC+++(8480) SW++ #+ S-- LS++ Hsp M+ A@ LM++ YB64m IC13
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