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In lugnet.org.us.lugola, Kevin L. Clague wrote:
> In lugnet.org.us.lugola, Brian Reynolds wrote:
> > 1) How sturdy are these things? The whole process revolves around air
> > pressure so I really want to get a sense of how much danger there is of
> > overpressure (specifically with the airtank), unreleased pressure over
> > time, and potential damage / wear and tear over time.
>
> My friend Doug has used them up to 30 PSI.
For models with a lot of cylinders I use a car tyre air compressor. I bought
the slightly more expensive one tha has a variable pressure limiter and set the
limiter to 20 PSI initially. This wasn't quite enough. 25 PSI was good for all
but the heaviest loads and 30 PSI really makes the models shift! I would
recommend 25 PSI for long running and 30 PSI for short bursts only, unless
you're prepared for some wear-out and have spare cylinders and valves to hand.
I use the football inflator attachment on the compressor but the hose slides off
eventually. I had thought of various ways to improve reliability of attachment.
The one downside of the compressor is that it's so noisy! You'll need a 12 Volt
6 Amp power supply too!
> Brian Reynolds wrote:
> >
> > 3) I have two cylinders
> > (http://www.bricklink.com/catalogItem.asp?P=2793c01) but one is brand
> > new while the other one is used and the used one takes longer to slide
> > in and out than the new one. The used one has some sort of gunk on the
> > tube that appears to be causing extra friction where the new cylinder
> > doesn't. Can this be cleaned off or is it just the product of age and
> > deterioration?
The gunk is grease that helps to seal the cylinder. There's grease in the
valves too (one of my old ones leaked under heavy use and I opened it) I think
the grease needs to be as thick as it is to seal the air in, but the thickness
makes it blob together rather than spread out.
> Brian Reynolds wrote:
> >
> > I haven't seen anything that would act as a plug for the third
> > opening so that air doesn't leak out of the circuit in the process.
I use a aerial in the end of a hose as a terminator, especially on redundant
valve ports that I don't want to allow to leak to the atmosphere.
Kevin L. Clague wrote:
>
> As pointed out by others, using the Flex system hose is better than using T's.
> In fact over long hose lengths it is better to use mostly flex system hose and
> use small pieces of pneumatic hose to connect them together.
>
> Long pieces of pneumatic hose tend to act a little like balloons.
You're right there! I notice the amount of air that leaks when you change the
valve in a system with lots of pneumatic hose.
I'm looking for a supply of each type of hose (rigid flex and squashy
pneumatic). Considering what I want to build, 100 metres of each type is not
too much for me to buy as a one-off if it comes on reels!
Kevin L. Clague wrote:
> I don't know if you consider my stuff beautiful, but I have made a lot of
> interesting things using pneumatics:
>
> My first pneumatic biped:
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38069
>
> My second pneumatic biped:
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=46671
>
> Two pneumatic adding machines:
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38075
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38283
>
> Some pneumatic creatures:
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38103
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38496
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=48796
>
> Some intro images:
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=46353
>
> Some basic computing circuits and pneumatic engines:
> http://www.brickshelf.com/cgi-bin/gallery.cgi?f=44968
Very nice models!
I have made all the standard electronic logic gates from pneumatic parts and got
over the leakage problems.
The OR/NOR/AND/NAND gate uses 6 valves and 2 cylinders - each input cylinder
pushing 3 valves. The tub wiring is a bit of a rats' nest! The same gate does
all 4 functions depending how you wire it. Reverse the output to go from OR to
NOR or AND to NAND and reverse the inputs to go from OR to NAND or AND to NOR,
just like electronic gates! The cunning bit is that the air takes 2 parallel
routes when the inputs are 01 or 10.
The XOR/XNOR/Parity gate uses one cylinder and one valve for the first stage and
2 cylinders and 4 valves for the second. The key principle is to swap the air
connections without any leaks occurring - the 'exhaled' air has to be routed
right back to the first stage. A Parity gate uses more 2Cyl+4Valve stages in
the same way as the second stage, though I haven't built one yet.
A flip-flop first appeared in the alternative model of 8868 Crane Truck. It
uses 2 cylinders and 2 valves and goes through the sequence 00,01,11,10 (gray
code!), where 0 is down and 1 is up. The crane truck was what first got me
interested in pneumatic logic.
Further pairs of cylinders and valves can be added in the flip-flop sequence. I
drew the diagram for a six-legged robot that would move one leg forad at a time
then all six back together. The main loop is a seven-set flip-flop and each leg
is a 2-set flip-flop with the last movement ynchronising with the main loop.
The seventh stage in the main loop reverses the whole system for the
simultaneous backward movement of all legs together.
I used flip-flops and an XOR gate to make a 10-step pick and place robot. The
robot extends, grabs a pen, retracts, turns at the elbow, turns at the wrist,
extends, drops the pen in a pot, retracts, turns back at the elbow, turns back
at the wrist and loops round again continuously. This is an ideal application
for the air compressor as six pump cylinders soon result in aching hands!
Notice that the extension/retraction happens twice in the sequence. This is
what the XOR gate does. Two large cylnders in parallel with the 2 small ones on
the grab move the 4-valve part of the XOR gate. The limit for 1 cylinder moving
valves is about 3 valves.
I did the logic for a four-joint Octopus arm that would place its arm on an
object, curl its arm around it, pick it up and uncurl its arm in reverse
sequence. There are 4 cylinders and 4 valves on the arm and 12 cylinders and 20
valves on a 32x32 board at the side!!! The logic for reverse sequences is
horrendous (especially avoiding leaks).
I've also succeeded in getting pneumatic cylinders to stop in the middle (for
Excavator steering etc...). This requires a set of 3 valves driven by 2
cylinders, where the valves are not all in the same position at once (ie.
there's a smaller offset between their levers). They're sprung together with
small white belts. This system is under further development and when I get a
backhoe excavator I'll cross it with the 4x4 jeep to make a 4x4 4-wheel
pneumatic steered excavator with self-centring steering and backhoe!
Sorry, no pictures yet but there will be when I get a digital camera! Meanwhile
I'm happy to discuss things and help out.
Mark Bellis
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Message has 1 Reply:
 | | Re: Lego pneumatic systems overview?
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| (...) [snip] (...) Thanks! (...) Mark Terrabain invented a single piston, single switch AND gate, but it only has one pressure output, so you have to retract the pistons with some external force like rubber bands. I invented a single pison, dual (...) (21 years ago, 26-Sep-03, to lugnet.org.us.lugola, lugnet.technic)
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Message is in Reply To:
| | Re: Lego pneumatic systems overview?
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| (...) My friend Doug has used them up to 30 PSI. (...) I don't know what the maximum allowable pressure is, but 30 PSI is probably a good upper bound. It depends on which direction you are trying to move the weight. If you are trying to move it (...) (21 years ago, 23-Sep-03, to lugnet.org.us.lugola, lugnet.technic)
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