Building : 8303


Building / 8303	8302 \| 8304

Subject:	Re: Analogue Control of Pneumatics
Newsgroups:	lugnet.build, lugnet.general, lugnet.technic
Date:	Wed, 21 Mar 2001 10:51:26 GMT
Viewed:	971 times

"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

Message has 2 Replies:

		Re: Analogue Control of Pneumatics
In real life pneumatic is not used where more than two position is accuired, and when it is done ither more pneumatic cylinders are placed after each other to make more fixed positions. Or there is placed an hydraulic brake on the cylinder to holde (...) (23 years ago, 21-Mar-01, to lugnet.build, lugnet.general, lugnet.technic)

		Re: Analogue Control of Pneumatics
(...) Ok. So you can't do it with pneumatics. Looking around for alternative ways of making a power steering mechanism, I found this link (URL) which gives an RCX based motor driven mechanism that might be of interest to others. Al Telanco (23 years ago, 22-Mar-01, to lugnet.build, lugnet.general, lugnet.technic, lugnet.robotics.rcx)

Message is in Reply To:

		Re: Analogue Control of Pneumatics
(...) Oops! Sorry about that. (...) 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 (...) (23 years ago, 20-Mar-01, to lugnet.build, lugnet.general, lugnet.technic)

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