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Gallery, Projects and General => The Design Shop => Topic started by: sparky961 on March 08, 2017, 12:51:22 AM

Title: Four Bar Linkage Design Help
Post by: sparky961 on March 08, 2017, 12:51:22 AM
Can anyone tell me if a four bar linkage can be made in such a way that something attached to one of the bars can be made to orbit around a known, fixed point?  I know... it's hard to visualize.  I'm trying to think up a way to have a "virtual" pivot point in a mechanism, without having any connections at that point.

In the attached (very) quick sketch, C is the centre point what I want X to rotate around.  X needs to be affixed to the base, B, by some sort of linkage, slide, or whatever.  Y shows another position of X on the arc of travel.  Nothing can be attached to C.  Think of X as a cube or rectangular block with 3 dimensions.

Simple and rigid, with the ability to lock and unlock to reposition easily.
Title: Re: Four Bar Linkage Design Help
Post by: efrench on March 08, 2017, 03:37:05 PM
It looks like you have the start of a design for a goniometer.
Title: Re: Four Bar Linkage Design Help
Post by: sparky961 on March 08, 2017, 05:46:14 PM
Quote from: efrench on March 08, 2017, 03:37:05 PM
It looks like you have the start of a design for a goniometer.

Well, I had to Google that one... Good guess but try again. :)

In looking around tonight, I found the Peaucellier-Lipkin linkage, and thought that might be promising.  But it still has a physical pivot point, which is what I'm trying to avoid.





Sorry for the Russian... the animations are nice though.
Title: Re: Four Bar Linkage Design Help
Post by: efrench on March 08, 2017, 09:58:34 PM
This should satisfy your criteria: http://www.mekanizmalar.com/looney_gears.html  :coffee:
Title: Re: Four Bar Linkage Design Help
Post by: sparky961 on March 08, 2017, 11:00:53 PM
Finally, I just came up with one candidate that could work.  Maybe this will help to elicit other ideas too, seeing more what I'm after.

In the attachment, the dashed line shows an extension to the "virtual pivot point" that I mentioned earlier.  I've included the same letters as I did in the original thread so you can see how it relates.
Title: Re: Four Bar Linkage Design Help
Post by: mc on March 10, 2017, 03:18:36 PM
My immediate thought is mountain bike suspension.

I'm sure there used to be an online simulator, but my googlefu is failing.
Only thing I've found is http://www.bikechecker.com/ which is downloadable software. It's £20 for a personal license, but it looks like you do get a limited functionality demo mode. Might be worth a try.
Title: Re: Four Bar Linkage Design Help
Post by: tom osselton on March 10, 2017, 04:47:47 PM
You might try this.
http://blog.rectorsquid.com/linkage-mechanism-designer-and-simulator/
Title: Re: Four Bar Linkage Design Help
Post by: sparky961 on March 10, 2017, 08:21:03 PM
Quote from: tom osselton on March 10, 2017, 04:47:47 PM
You might try this.
http://blog.rectorsquid.com/linkage-mechanism-designer-and-simulator/

Very cool.  I'm going to take a look at that.  I'm very impressed by the documentation, given that it's a free program.

I have a working solution, which I'm planning to post here later when I can put together some screen shots.  However, there are some things I'm not completely satisfied with yet and this suggestion may help me to work out those kinks.