Newsgroups: comp.robotics
Path: brunix!uunet!wupost!csus.edu!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Poor man's pneumatics
Message-ID: <nagleCBMsID.H63@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <1993Aug11.113844.2833@ohstpy.mps.ohio-state.edu>
Date: Thu, 12 Aug 1993 05:27:48 GMT
Lines: 35

edharris@ohstpy.mps.ohio-state.edu writes:
>Since making accurate cylinders and pistions with relatively tight seals is
>rather difficult for the hobbiest without access to a machine shop, here are a
>couple of low cost, low tech alternatives:
>1) For fairly big stuff you can use close fitting cardboard boxes or tubes (so
>that they slide past each other) with some kind of end cap (wood or heavy
>cardboard). Now of course, as is these guys would leak like crazy if you pump
>air in. So instead, put a heavy lawn type garbage bag inside the counter-
>opposed boxes and seal it up except
>for an air inlet port.
       Now that's low-end.

>2) Use dryer duct with end caps in a similar manner as above. Though for high
>air pressure you'll need a cardboard or PVC tube to keep the stuff from 
>blowing up like a balloon.
       Now we're talking.  There's a number of variations on this theme.
One is to use pressure to straighten a flexible hose.  There are hoses that
have a restraining mesh that keeps them from ballooning, starting with
better garden hose and running up to auto brake hose.  Chico McMurte
builds performance art devices powered that way.  

       Pneumatic bellows have a long history; check out an old player piano.
Player pianos are usually run with a vacuum supply, so the "tape reader"
will suck the piano roll up to the "read head", rather than pushing it away.
The actuators thus pull, rather than push.  Each actuator (called a 
"pneumatic") is two blocks of wood connected by a hinge.  A fabric bellows
connects the two blocks, and is attached with glue.  A nice do-it-yourself
project, if you're into woodworking.  Aquarium tubing and fittings are
suitable plumbing for such gadgets.  Solenoid-operated pneumatic valves
are available for controlling the air/vacuum.

       This level of technology appears in animated figures like 
museum dinosaurs (although "Jurassic Park" uses fully-servoed hydraulics).

						John Nagle
