Newsgroups: comp.robotics
Path: brunix!uunet!ftpbox!mothost!binford!mcdchg!mcdphx!schuch
From: schuch@phx.mcd.mot.com (John Schuch)
Subject: Re: robotic hydraulics infomation resources.
Message-ID: <1993Apr10.061834.25423@phx.mcd.mot.com>
Keywords: hydraulics, robotics.
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References: <1phk6jINNbgo@uk-news.uk.sun.com> <1993Apr5.214644.16672@phx.mcd.mot.com> <C569vE.13M@ecf.toronto.edu>
Date: Sat, 10 Apr 1993 06:18:34 GMT
Lines: 41

In article <C569vE.13M@ecf.toronto.edu> hertz@ecf.toronto.edu (HERTZ ROGER BARRY) writes:
>In article <1993Apr5.214644.16672@phx.mcd.mot.com> schuch@phx.mcd.mot.com (John Schuch) writes:
>>
>>"Hydraulics" and "small robots" are not usually used in the same
>>sentence. Or you have a different perception of 'small.'
>(s.d.)
>
>Why is this?  I have heard this as well.  Is there problems with
>scaling down hydraulic technology, and keeping the cost competitive?

Hydraulics is an order of magnitude more than pneumatics. More what?
Expensive, powerfull, noisey, messy, heavy, dangerous, etc.
>
>By the way, what is your perception of small?  Cat sized, mouse
>sized, roach sized, flea sized?

Hydraulic robots smaller than a Volkswagen Bug are rare.

>To the original poster: why not use pneumatic cylinders filled with
>oil?  Is cheap and quiet.  Just a thought.
>
The problem here is with the seals in the cylinders. All but the really
cheap pneumatic cylinders are air tight when they are new but MOST 
cylinders start to leak around the seals after as few as 100 cycles.
When you are running them with air, these tiny leaks are of no concern.
But when your creation piddles transmission fluid all over the dining room
floor, you may have a lot to worry about.

I think the main benefit of using hydraulics (aside from brute power) is
that you can have very fine flow control with virtually no fluid
compression. You will see this used where it is far less important where
the cylinder ends up than the speed at which it moves.

There ARE hybrid systems out there that use pneumatics (compressed air)
to pressurize a hydraulic reservoir. The pressurized hydraulic fluid is
then used to run the cylinders. This gives you the fine control without
dealing with those noisey hydraulic compressors.

John


