Subject:
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Re: SSClagorpion
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Newsgroups:
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lugnet.technic
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Date:
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Thu, 15 Apr 2004 11:55:56 GMT
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Viewed:
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8622 times
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In lugnet.technic, Kevin L. Clague wrote:
> Pressure is in pounds per square inch. So if we know the area of the face of a
> piston, and we know the pressure we can determine how many pounds a single
> piston can lift.
>
> Force = Pressure * Area
>
> A pneumatic piston face is about a half an inch in diameter. The area then is
> pi times diameter, or about 1.6. Four pistons then have the combined area of
> 6.4.
Mark Riley was nice enought to point out the errors in my math. The area of the
piston care is pi * r^2 = 0.2
Four times that is 0.8.
So the minimal pressure needed is 10 pounds / 0.8 square inches or, 12.5 pounds
per square inch. Still well below the 32 PSI upper limit for LEGO pneumatics.
The next question is, how easy is it to get to 13 PSI with LEGO based
compressors.
If we double the number of pistons, we'd only need to get to 6 PSI, but will
this really make much difference on piston transition time.
The pistons that do the most work (force through a distance) are the horizontal
pistons. They actually make the distance term non-zero.
Back to compressors for a second...... There has always been this debate about
which pumps are better, small pumps or large pumps. Small pumps provide less
piston face are than larger pumps, and can drive the pressure in a closed system
to max pressure quicker than the large pumps (even with spring removed)... but a
pneumatic sequencer (motor for example) is not a closed system. It is always
releasing pressure when the pistons are switching direction. A second test that
measures the RPM of a pneumatic engine (motor?) using a small pump vs. a large
pump showed that the large pump did better.
One of the issued with large pumps is that they are large... large enough to
affect the minimum scale of a compressor, and therefore the creation being
made......
I'd like us to make Scorpion completely out of LEGO parts. I'm not a full time
purist, but typically this is my goal so that others can make copies. I guess
also that I'd like to make it out of currently available parts. This rules out
the use of the original single ported pistons. Unfortunatly this also rules out
the use of:
http://www.bricklink.com/catalogItemPic.asp?P=4692
Using two of these and a double ported piston would give us a double acting
pump, instead of the single action pumps lego makes. Presumably this would
reduce the inherent amount of friction in the compressor.
Kevin
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Message has 2 Replies:
 | | Re: SSClagorpion
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| (...) ... (...) With twice the pistons, the pressure is not as great, but the volume of air would be doubled, right? Using logic, not physics, I think once the pressure is built up (to 13 psi) the compressor may have to do less work to keep it (...) (21 years ago, 15-Apr-04, to lugnet.technic)
| | | Re: SSClagorpion
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| (...) A few things spring to mind about this: 1. I usually run robots from a car tyre air compressor at 25PSI. This gives good performance with 1-2 large cylinders moving at a time. Using 6 large pump cylinders as the air source, performance is half (...) (21 years ago, 15-Apr-04, to lugnet.technic)
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Message is in Reply To:
| | Re: SSClagorpion
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| (...) Hmmmm.... interesting question. I don't know much pneumatic theory, but..... Pressure is in pounds per square inch. So if we know the area of the face of a piston, and we know the pressure we can determine how many pounds a single piston can (...) (21 years ago, 15-Apr-04, to lugnet.technic)
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