Subject:
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Re: CD auto feeder project
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 5 May 2004 22:37:59 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail^saynotospam^.net>
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Viewed:
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927 times
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David Glynn wrote:
> > If you take a large pneumatic cylinder and connect a hose to the bottom
> > fitting (say) then pulling the actuator arm upwards creates a pretty strong • >> suction and pushing the cylinder down again releases it.
>
> Are you refering to the large pneumatic cylinder shown in this ebay auction?
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=19002&item=3191469136
> &rd=1
Yes - the yellow ones on the left.
The 'normal' use for those things is to pump air in the bottom tube to make the
cylinder extend - or pump air in the top to make it contract. However, if you
left the top hole open to the air and connected a short hose from the bottom to
a suction cup - then pulling up on the cylinder would "really suck" :-)
> In that case linking it or a pair up motor in the same way that you connect
> the pumps I could create and store a vacume in the tanks, and then activate
> a valve when ever a vacume is needed - that would be two motors and one
> outputs used up (the motor for creating the vacume does not ned to be
> controled by the RCX, am I right? I'm thinking something along the lines of
> Ralph Hempel's pressure switch).
Well, no - that's the problem - to 'pump' the thing and build up a good vacuum
in a tank you need a non-return valve. There are no non-return valves in the
'current' set of Lego pneumatic parts - however (as someone pointed out), they
can still be found on the used parts market.
However, I doubt you need that much suction. The amount of air under one of
those small suction cups is pretty small - and you don't need a perfect vacuum
to get it to stick and lift something light like a CD. If you need more lifting
power, you could just use several of them.
It's generally nicer to build things like that out of 'current' parts because
that allows more people to replicate your model or use your techniques in some
other way - which is a good thing for 'community' and all that.
> I think the pressure switch (and it's motor) would need to be placed at the
> opposite end of the arm form the suction cup, this would prevent too much
> weight been out at the end of the arm which is about 12"/30cm long (in my
> mind). It would also serve as a counter weight then. This means that the
> lenght of the hose would be that plus some more, possible as long as
> 24"/60cm - I don't think this is short.
That would definitely be a problem. Those hoses are designed to hold pressure.
When you suck hard on them, they tend to collapse flat. Also, you have to remove
not only the air under the suction cup - but also the air inside the hose. The
longer the hose, the more air you have to remove in order to drop the pressure
under the suction cup by the same amount.
I don't see why the arm has to be that long. I'd use an underslung conveyor belt
that's about as long as the diameter of a CD. The conveyor can be supported at both
ends and could carry the weight of the motor and the pneumatic cylinder. The hose
would only have to be a couple of inches long.
> I see I have a busy summer ahead of me!
Yeah! Sounds like fun. I just love pneumatic machines in Lego - when they
are computer controlled, they are just fascinating to watch and they make
satisfying hissing sounds like an old steam engine.
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://www.sjbaker.org
Projects : http://plib.sf.net http://tuxaqfh.sf.net
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Message has 2 Replies:
 | | RE: CD auto feeder project
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| (...) Don't those hard plastic tubes fit over the cylinder connectors? I know they can bind the flexible hoses, so a small "boot" to bridge the gap wouldn't be able to suck together very much. That would reduce the problem of length, at least. Andy (20 years ago, 6-May-04, to lugnet.robotics)
| | | Re: CD auto feeder project
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| (...) Note you can also use the same effect to make an all-Lego suction pump (without the checkball valve). The trick is to cycle a piston and a standard valve together. Hook the central port on the valve to the airtank (or whatever else you want to (...) (20 years ago, 9-May-04, to lugnet.robotics)
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Message is in Reply To:
| | Re: CD auto feeder project
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| Steve, thanks for the pointer, I'll be spending some time going over Rob's window walker figuring out how he did things. (...) I'd be suprised if they were! Though I did find the perfect suction cup on-line: (URL) get more perfect then that. (...) (...) (20 years ago, 5-May-04, to lugnet.robotics)
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