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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Thu, 25 Aug 2005 16:04:41 GMT
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Viewed:
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4619 times
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I think this diagram should explain the differences:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Building-Blocks/pneumatic_n-input_and_circuit.jpg
It is the N-input differential output AND gate, developed from your sketch.
I've used 2 switches for A, to gate the supply so that it doesn't leak. This
gives 2+4++4 switches for an N-input gate. The diagram shows 2+4 and more
modules of 4 can be added.
I'm including the 2 switches in the gate, since the two inputs are the positions
of switch banks A and B, as driven by the cylinders (B has a parallel pair).
The idea is that the output from another gate (at the circles bottom right) can
be connected to the input of another gate (at the inputs on the left) in order
to daisy-chain gates to make a combinational logic system.
In this case switch bank A is the source of the pressures you used as your
input. I've included them in the gate because the pressures should have a
source in the position of a part of the model, which would then move switch bank
A. Hence the position of that part of the model is your input into the logic
("IF grab is closed AND arm is retracted THEN rotate elbow" etc...).
When adding modules to this gate (imagine stage C like stage B but between it
and the cylinder), you can reverse the inputs to have A AND B AND !C (with a
free NOT gate), but you can't swap the output hoses on the right between stages
B and C because inside the gate they are not leak-protected. The leftmost
switches in each bank together make a pressure signal that leaks except when all
stages are set to "1".
------------------------------------------------------------------
My AND gate can have additional B stages added to it to make 3 or more stage
gates. I've yet to determine the leak protection requirements between stages of
that, but I'll look into it to see if either design can do more interesting
3-input functions such as (A AND B) OR C in one gate, eliminating the
propagation delays of daisy-chaining gates.
My 3+3 AND gate actually produces the same signals as this 2+4 gate, but
possibly only requiring 1 cylinder per switch bank if they are not attached to
moving parts of a model. This would be the case if I built the model like my
octopus arm, where I put enough cylinders and one switch on each moving joint,
to save weight on the arm, and put all the logic (24 switches in banks of 4, 4,
9 and 3) on a 32x32 baseplate, each with a pair of cylinders for three or four
and three pairs for the 9.
In my gate it's the two paths in the 0-1 and 1-0 states that are most confusing,
since if A is 0 and B is 1 the pressure goes along the same-side link one way
(A2-A3) and crosses from B to A and back to B the other way (B2-A1-B3).
---------------------------------------------------------------------
In the gate, the switches are the internal transistors, which is why I include
them. The input signals are either the differential pressures driving the input
cylinders, or the positions of the switches they drive.
---------------------------------------------------------------------
In lugnet.technic, Kevin L. Clague wrote:
(SNIP)
> But the moment you use gate pistons as muscle pistons, and the load exceeds the
> force produced by the gate pistons, your run the risk of locking up your state
> machine (whether you use differential pressure gates or single pressure output
> gates.)
>
> The other side of the coin is that if you do not use your muscle pistons as
> timing pistons, then you are back to assymetries in pistons making your walkers
> walk funny.
Yes, I use my gate pistons as muscle pistons, but sometimes buffer them with a
single 1-cylinder 1-switch stage. I make sure that only one thing moves at a
time, or if more than one, that there are AND and OR functions to cover every
possible state of the multiples, so that they must all remain pressurised in the
right direction until all have completed and so that nothing else can move until
they have all completed. It's generally too complex to do multiples, so I'd
rather avoid it and save a few switches!
----------------------------------------------------------------------
(SNIP)
> Hmmm... my goal when making a walker, is to have all the pistons be muscle
> pistons with as few timing only pistons as possible. Timing only pistons create
> delays that slow walking. By combining timing and muscularity in the same piston
> you can compensate for their assymetries. For example, when I tried to use a
> central timing circuit for SSC1 (the kind of design I think you are talking
> about) without any synchronization of the legs, one leg group lifted and dropped
> very nicely, and the other did not.
>
> Here is a central timing circuit:
> _ _
> A / \_/
> _
> B _/ \_/
>
> 0123456
>
> A and B's expansion controlled one leg group lift. A and B's contraction
> controlled the other leg group's drop. The assymetries between expansion and
> contraction caused the lift/drop of one leg group different than the lift drop
> of the other leg group.
>
> I had to instrument both the lift and drop of all the legs in each leg group to
> make sure I eliminated these assymetries.
(SNIP)
>
> Kevin
Then the ground being uneven might bring them back, since the legs would have
different loads!
Mark
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