Subject:
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Re: Brickfest Pneumatic Master and new Pneumatic Gate Circuits
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Newsgroups:
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lugnet.technic
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Date:
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Sun, 28 Aug 2005 18:56:24 GMT
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Viewed:
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5100 times
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In lugnet.technic, Kevin L. Clague wrote:
> Mark,
> I have studied and understand your 3+3 AND gate. A few years ago I made a
> simpler version of the same thing. My design replaces your six switches with
> one switch and mechanical linkages. Here is a picture of this AND gate:
>
> http://www.brickshelf.com/gallery/kclague/Computing/p5280034.jpg
>
> In my 1 AND gate, A and B each control a piston. The two pistons are
> connected base to base, not unlike the pneumatic boom controls in the 8421
> technic crane. One piston is afixed to a frame that also contains a single
> switch. The center of the switch is hooked to the pressure source. Given two
> pistons hooked together in this fashion the total amount of expansion due to
> both pistons can be:
>
> A B Sum Length
> C C 0
> C X X 1
> X C X 1
> X X XX 2
>
> If you extend the handle of the switch by inserting an axle connector and a #2
> axle between the switch handle, and the #1 Angle piece you use to connect to the
> piston, the extension length of the piston is the same length as the throw of
> the switch. The linkage between the pistons and the switch contains rubber
> bands. When both pistons are expanded, the switch handle is pressed away from
> the pistons. When one and only one of the pistons is expanded, the switch is
> pulled toward the pistons. When both pistons are contracted, the rubber bands
> stretch in an attempt to further pull the switch handle closer to the pistons.
>
> By moving the switch closer to the pistons, you can easily make an OR gate.
>
> http://www.brickshelf.com/gallery/kclague/Computing/p5280036.jpg
>
> This is the most cost effect AND gate that I know of that meets all your
> requirements. While too fragile to be put in-situ as a muscle piston, for pure
> computation it has the smallest pneumatic part count.
>
> I don't know that we'll ever see eye to eye on how to count pneumatic parts
> within our gates, but it does not matter to me. Whatever pneumatic circuit I
> make, I will tend to use whatever gate technology that is cheapest and meets the
> need.
>
> I've gained a lot of good knowledge from this discussion, and that is all my
> LEGO pneumatics exploration is about.
>
> I look forward to seeingmore of your designs in the future. I also look forward
> to reading any articles you write for BrickJournal. More is better!
>
> Kev
Yes, I can see how the 2-cylinder design is more cost-effective, particularly
since a Backhoe has 10 cylinders and only 7 switches. That allows more
cylinders to be used for AND and OR gates, saving the switches for XOR gates.
I've done some more study in order to investigate the 3-input gate, using the
4-switch module in multiple. This has shown me how the original 4-switch module
from your sketch is an AND gate in its own right, as long as the differential
pressure input is one input and the switch position is the other input. A
reverser between stages can invert the differential pressure input, making
endless possibilities for the logic function of the system, by allowing the
output to be high in 1, 3, 5, or 7 of the eight combinations of three inputs.
Seeing the 4-switch module that way, and using it in multiple, makes for a gate
without any extra propagation delays due to daisy-chaining. It's also more
cost-effective, since only four switches are required. For a gate with two
switch position inputs (rather than one switch position and one differential
pressure), one of the switches driven by "A" can be trimmed from my diagram,
making a 1+4++4 gate.
I still like the elegance of my 3+3 design, especially because it's symmetrical,
but the most elegant solution is rarely the sleekest! In pneumatics there is
more to be said for reducing parts count because the parts are so expensive.
That's where 1+4++4 scores over 3+3++4.
Overall this means that a set of combinational logic can be achieved with
4-switch AND modules and 4-switch reversers such that there is only a single
propagation delay between states, which is good for machines whose timing is
critical, such as your walkers.
Mark
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