Subject:
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Re: Classic timing circuits and XOR gates (long)
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Newsgroups:
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lugnet.technic
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Date:
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Mon, 8 Aug 2005 23:14:34 GMT
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Viewed:
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3170 times
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In lugnet.technic, Kevin L. Clague wrote:
(SNIP)
> I was motivated by Mark Bellis' "pick and place" pneumatic arm, that picks
> things up from one place, and drops them in another. Mark's pneumatic arm does
> not use my asynchronous design technique, and never locks up. It was Mark's use
> of XOR gates to control the wrist that intrigued me.
>
> XOR is a kind of calculation that computers use based on boolean logic.
> Basically XOR tells you when two things are the same or different.
>
> Mark used a classical pneumatic timing circuit used to create pneumatic engines
> (as described on Dr. C. S. Soh's wonderful pneumatic website
> http://www.fifth-r.com/cssoh1/develop.htm).
>
> Pictorially this sequence looks like this:
>
> http://www.brickshelf.com/cgi-bin/gallery.cgi?i=417362
(SNIP)
> Here is a collage of four pictures show how an XOR gate works. The stand alone
> switches at the bottom of the picture represents the values being driven into
> the XOR gate.
>
> http://www.brickshelf.com/cgi-bin/gallery.cgi?i=433934
(SNIP)
> the pistons have to push and pull five switches. This requires very high
> pressure, making walking slow (again :^). I got around this problem just as
> Mark Bellis did in his "pick and place 'bot", by proving adding a second piston
> to those pistons that have XOR gates on them.
>
> I guess I've been droning on...... sorry.
>
> In studying the possibilities of six piston timing circuit and XOR gates I came
> up with all combinations of XORs for the six pistons. The XOR patterns break
> down into three groups:
> 1. Piston expands and immedialy contracts (or visa versa) (5/1,1/5)
> 2. Piston expands, waits for one piston transitions (or visa versa) (4/2,2/4)
> 3. Piston expands, waits for two piston transitions (or visa versa) (3/3) • (SNIP)
> Well, this is another one of my long diatribes about pneumatics, but usually
> there are at least a few people who wade through a long post like this.
>
> I hope it is comprehensible.
>
> Kevin
Can I suggest that in order to avoid leaks (very important in walking robots!)
you use the full XOR gate from my diagram:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/PnP-Robot/pnp_robot_circuit.jpg
The single switch is the right one of two moved by the wrist and the four switch
reverser is made from the top four of five moved by the grab. The outputs to
the XOR result cylinder come from the middle ports of the switches to avoid
leaks. This is important since your XOR result will be driving load-bearing
cylinders.
The additional cylinders pushing switches is simply power versus load. One
cylinder to two switches with a bit to spare, so 2 cylinders can do 5 switches.
I don't recommend cylinders moving one way and then immediately the other way as
this can lead to race conditions (going into undesirable lock-up states). The
principle is to always have at least one other cylinder movement between two
movements of the same cylinder.
For my octopus arm (circuit being drawn) I put one switch on each joint and used
a 32x32 plate for the logic, knowing that none of those cylinders was load
bearing, so that none of them would leak. I used 24 switches on the logic
board, but that was reduced logic to optimise switch use. It used quite a few
stoppers too (aerials in short tubes blocking unused switch ports to prevent
leaks). This circuit was based more on combinational logic than on loops.
For my 6-legged robot (one leg forward at a time and all back together) I used a
central loop of 7 cylinders each with 2 switches. Six of the seven sets of
1c+2s each drove a leg loop of 1c+2s and 1c+3s. Each leg would go up, forward,
down and tell the central loop to advance to the next leg. When the loop got to
the seventh cylinder it reversed, but supplied air to pull all legs back
together. This used fewer stoppers, about 2 per leg. This circuit was based on
one main loop and six smaller loops, each enabled in turn by the central loop.
For SSClagorpion do you have 8 legs in four groups of 2?
You can use XOR gates on pairs of legs to show whether they are both in the same
state or not, and not enable the next part of the circuit till they are.
The XOR gate is far more important to the sequencing of the P+P robot than just
hanging off for an auxiliary device. The cylinder driven by the XOR gate must
have a switch that enables the supply to two halves of the circuit, such that
the circuit can't continue till the XOR output has moved. In the P+P robot I
have the grab on one side of the circuit and the elbow and wrist on the other
side. The extension is the XOR result as it operates twice per cycle. It has
an enabling switch (middle of diagram) that supplies air either to the grab
cylinders (via the wrist switch) or to the elbow cylinders (via the bottom grab
switch) but never both at the same time. The wrist cylinders just follow the
elbow switch because the wrist always moves after the elbow. This circuit was
based on one main loop split into two halves by one XOR gate.
I shall have to experiment with multiple XOR gates in a loop to prove the
concept. I don't recommend throwing four at it immediately!
BTW I've been working on a circuit for a pneumatic "shuttle" that drives a
2-cylinder steam engine along a track and back again, stopping when it hits the
end-stop, doing a function, then reversing when the function has completed. The
idea is to do a function at each end of the track and then travel along it.
Hope this too is intelligible!
Mark
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Message has 2 Replies:
 | | Re: Classic timing circuits and XOR gates (long)
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| Hi People, I really appretiate the circuits Mark has put up, they are very instructive, and between you you guys are taking Lego pneumatics before I have seen it go before. But - in your diagrams, you do not label the components - which make them (...) (19 years ago, 9-Aug-05, to lugnet.technic)
| | | Re: Classic timing circuits and XOR gates (long)
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| (...) (SNIP) (...) your diagram is particular to your overall circuit, right? (...) Absolutely..... I've found that a single can do the task, but only at maximum pressure. (...) Agreed... I had to add race killing by synchronizing leg up and down (...) (19 years ago, 9-Aug-05, to lugnet.technic)
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Message is in Reply To:
| | Classic timing circuits and XOR gates (long)
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| I've been making progress on SSClagorpion draft 1..... Inchworm ( (URL) ), Quad242 ( (URL) ) and Hes363 are precursors to SSC in many ways. On Inchworm I invented an asynchronous design technique for creating pneumatic circuits with complex (...) (19 years ago, 5-Aug-05, to lugnet.technic)
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