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jorgeopesi

Z-bar linkage help

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I am working on another wheel loader and I have again the same problem, the Z-bar linkage. In my previous loaders I solved it with hours and hours of tests to achieve the perfect travel but this time I wanted your help because I have seen a lot of pics and brochures of machines but I don´t find what I am looking for, I want the mathematical formula or whatever to be able to make arms more quickly, what allows to know the measurements and position of the different pieces depending on the size of the cylinder, arm and anchors of the bucket, it is a difficult question because even Lego wheel loaders haven´t got realistic bucket movements.

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I'm not very well at maths, but when i think about your problem (and if  i understood it correctly) i end up with nonlinear equations, that could illustrate the correlation between cylinder position and bucket angle. This correlation won´t be proportional, due to the trigonometric geometry of the linkage. If you set the dimensions of the linkage elements as variables, the formula won´t be solvable in a way that it gives you one geometry for a given bucket movement range/speed. So you will have to calculate it seperately for every geometry version.

If you have a CAD software with kinematic simulation it may be useful, but i don´t think you will save much time compared to real life testing. Another problem would be, that the maths doesn´t care about bad angles in your linkage, e.g. when the cylinder and the Z link are positioned close to 0° or 180° to each other.

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1 hour ago, Lucullus said:

I'm not very well at maths, but when i think about your problem (and if  i understood it correctly) i end up with nonlinear equations, that could illustrate the correlation between cylinder position and bucket angle. This correlation won´t be proportional, due to the trigonometric geometry of the linkage. If you set the dimensions of the linkage elements as variables, the formula won´t be solvable in a way that it gives you one geometry for a given bucket movement range/speed. So you will have to calculate it seperately for every geometry version.

If you have a CAD software with kinematic simulation it may be useful, but i don´t think you will save much time compared to real life testing. Another problem would be, that the maths doesn´t care about bad angles in your linkage, e.g. when the cylinder and the Z link are positioned close to 0° or 180° to each other.

Thanks, I thought exactly what you have written but the problem is that I am not smart enough to go further... :blush: , the program would be useful but I preffer the real mode. 

49 minutes ago, pagicence said:

Have a look a this liftarms solutions, maybe you'll get inspired. Brickshelf link

Also try building a wheel loader with this kind of mechanism. JCB 413S Agri Wheel Loader and JCB 437 Agri Wheel Loader

I know that brickshelf page and of course will be perfect to build a stronger arm, as I am building a specific wheel loader I always try to do its real linkages.

 

After some hours of test I get this, I have to build a stronger arm but the travel and the movements are in scale with the real machine so the hard part is done.

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I still want to know everything about linkages so if you know something it would be a pleasure to read it.

Edited by jorgeopesi

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With a quick googling I found this program.

http://blog.rectorsquid.com/linkage-mechanism-designer-and-simulator/

I guess there are many other free programs as well.

Search words: kinematics, editor, mechanism, linkage, etc

Once I started programming a software like for these things. I you can wait 4-5 months, I'll be back with the program :tongue:

Edited by Lipko

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1 hour ago, Lipko said:

With a quick googling I found this program.

http://blog.rectorsquid.com/linkage-mechanism-designer-and-simulator/

I guess there are many other free programs as well.

Search words: kinematics, editor, mechanism, linkage, etc

Once I started programming a software like for these things. I you can wait 4-5 months, I'll be back with the program :tongue:

Wow direct to my favorite pages,thanks I have a lot of to read and learn, I envy your programing skills.

I like a lot this page :laugh: .

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Edited by jorgeopesi

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This matter brings me back to 1 year ago, when I was facing the same with my Volvo Loader (in my case, the linkage is a little different than the standard Z-linkage).

I worked a lot with autocad, but at the end the result was very good.

 

Here is a preview.

test.jpg

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What I have done when building wheeled excavator was finding blue prints and scale them to pneumatic cylinder size first. Most excavators use same sized cylinders for main boom and bucket. I have looked at front loaders and it seems that it is usually the same case. When you scale it to cylinders size you will most of the time end with wheels out of the scale, but that is the desicion you have to make - realistic bucket movement or realistic wheel size. Then I have build each section of the arm from technic bricks and plates with pivot points as close to original as possible. After that you can optimize till you are satisfied.

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I usually do the same I preffer perfect functionality above scale, the part I like more is the central part of the linkage, small changes in it makes different bucket travels.

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When building my bucket-loaders/swingloaders (e.g. http://www.brickshelf.com/cgi-bin/gallery.cgi?f=566905), I had to deal with these issues, too. For me, it's the most annoying part of the whole model, and I solved it by a lot of trial and even more errors.

The big disadvantage of the Z-linkage is the fact that the bucket is not balanced while moved vertically. So you always have to activate both (pairs of) cylinders (LAs, respectively) at the same time - otherwise the load will be dropped while being lowered.

Does anyone here have a clue for this issue?

The alternative for the Z-linkage ist the P-linkage (like in 8455 or 8862; the P-linkage provides the bucket's balance by itself (if constructed correctly).

Edited by Timewhatistime
mixed both types of linkages

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My time used in the Z-linkage is always looking for the best bucket travel in fact my two previous loaders and this one having diferent sizes they keep the same bucket position when the arm cylinders are working, I thought it was the objective of that linkage. Of course in your loader type  achieve that is very difficult.

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