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In lugnet.technic, Mark Bellis wrote:
(SNIP)
> I have succeeded in directly cascading trinary pneumatic stages (where cylinders
> stop in the middle).
>
> This is a direct development of my mid-stop pneumatic JCB steering mechanism,
> which I first described here two years ago:
> http://news.lugnet.com/org/us/lugola/?n=916 (second paragraph from the bottom).
>
> I've taken some photos and will post them as soon as they come back from the
> developers. They will include the trinary system in all positions, as well as
> the Octopus Arm logic that I mentioned earlier. There will also be my earliest
> use of my trinary actuation mechanism and a pressure limiter (I'm sure quite a
> few people have their own versions of the latter).
>
> I took the actuation stage and the steering stage from my earlier work and added
> a combination of the two in the middle to make two cascading stages.
>
> I hope this will be useful for your walkers Kev. It's different from the way
> you were doing it. I have used opposing pistons for more power, and also extra
> frame members in tension to improve strength.
>
> The mechanism works quite well but I will keep improving it, probably by beefing
> up the power to improve reliability (with apologies to vegetarians :-) ). This
> might involve adding more cylinders to ensure that the mechanism reliably
> reaches its maximum distance from the centre position in both directions. The
> switch connections and the actuation mechanism that keeps the switch levers
> exactly the right distance apart are my own unique designs, which work well.
>
> I remember how it took quite a while to work out exactly how far apart the
> switch levers needed to be and which parts to use to achieve that distance.
>
> I wish my digital camera would arrive so that I could speed up posting!
>
> Mark
Here are the pictures (at last!)
They show the control stage, cascade stage and steering stage of Trinary
Mid-Stop pneumatic logic.
Start in the centre position:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Trinary-Logic-System/cascaded_trinary_logic_evo1_1.jpg
Moving to the left:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Trinary-Logic-System/cascaded_trinary_logic_evo1_2.jpg
Moving back to the centre:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Trinary-Logic-System/cascaded_trinary_logic_evo1_3.jpg
Moving to the right:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Trinary-Logic-System/cascaded_trinary_logic_evo1_4.jpg
Close-up from the side:
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Trinary-Logic-System/cascaded_trinary_logic_evo1_zoom.jpg
Original switch geometry (robbed of hoses!):
http://www.brickshelf.com/gallery/mbellis/Technic/Pneumatics/Trinary-Logic-System/first_mid_stop_steering_switch_layout_1999.jpg
I have developed the system further to improve reliability, also eliminating the
centre switch in each stage - you see that the control stage already has its
centre switch unconnected in this evolution. Evo 2 will be photographed with my
next batch of MOCs.
Using only studless beams requires more framework than using studded ones,
especially the tensile members that absorb the pressure of two cylinders pushing
against each other. Using single cylinders is possible if the auto-extension
can be countered with a belt or elastic band that causes the cylinder to
auto-centre instead when pressure is applied to both ends.
Depending on belt tension and input pressure, my design could also be used to
make a 7-stop pneumatic system! This is getting closer to hydraulics, which are
much easier to control to any desired position, except in the LEGO system that
doesn't have them! I don't recommend using water with pneumatic parts - I tried
it once in order to make a fire engine but the non-return valve of the old
pneumatic system soon failed. The more I experiment with the complex and
expensive LEGO parts, the more I decide to understand what is their original
design intent and stick to that.
Mark
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