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"Alvin Telanco" <78of560001@sneakemail.com> wrote
> Just to clarify my original post. I am interested in more exact control of
> both position and applied force.
>
> I am interested in trying to build mechanisms found in read life things • like
> cars and was thinking about power steering servos when I started playing
> about with pneumatics. Perhaps this is a bit hard for Lego:-)
Hi Al,
what you ask is not possible because the Lego pneumatic system is,
precisely, *pneumatic*. In real life cylinders that are designed for
position control are hydraulic and not pneumatic ones. This difference is
very important because you can compress a gas but cannot compress a liquid.
A pneumatic system has a very high degree of elasticity, and in practical
terms this means that position is a function of both the applied pressure
AND the encountered resistance.
Translating this into a mechanical example, the difference is the same you
find between a rigid and an elastic link. Suppose you have two movable parts
(1 degree of freedom) in a Lego mechanism: if you connect them with a beam
you can always tell the position of the first part knowing the position of
the second (or vice-versa). While if you connect them with a rubber it's
very difficult to tell or to adjust the position of one part simply acting
on the other, because that position depends also on the properties of the
rubber and on the resistance the part puts to be moved.
Elastic systems in general are not the proper ones to use to control a
position, because while the load changes you must continuously change the
applied force (pressure) to keep the position.
Hope this helps, though I'm not an engineer nor a physicist so I'm
definitely not the best person to explain this.
Mario
Lego web page: http://www.geocities.com/mario.ferrari/lego.html
LUGNET member page: http://www.lugnet.com/people/members/?m=22
Proud member of ItLUG: http://www.itlug.org
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