Subject:
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Re: Dave Schilling's pneumatic parlor trick
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Newsgroups:
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lugnet.technic
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Date:
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Tue, 16 Aug 2005 21:58:34 GMT
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Viewed:
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3573 times
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In lugnet.technic, Nathan Bell wrote:
> > > Any ideas why this happens? For those of you who know right away (you know who
> > > you are ;^), lets let the uninitiated talk about this and see if they can figure
> > > it out!
> > >
> > > Hint: As you pump more and increase the pressure, the piston gets slightly
> > > harder to manually compress. The difficulty of compressing the piston manually
> > > does not increase dramatically.
> >
> > Is it because the extension side of the piston face has a greater surface area
> > than the retraction side? The connection between the piston face and the piston
> > rod accounting for the difference.
> >
> > Steve
>
> Yep, that is why pistons push better than they pull.
This phenomemon is the reason why any pneumatic mechanism (such as steering)
that you intend to stop in the middle (with pistons at the half way point)
should always use two opposing pistons. This equalises the total piston area
for each movement direction.
However, this might lead to extra compressive force on the mechanism, since both
pistons will be biased to push towards the middle rather than pull away from it.
I've also found that large cylinders aren't very good at pulling from their
fully-extended position, so in pneumatic logic systems I use axle connector #5
on the switch next to the piston to stop the piston expanding fully.
Mark
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