assembly 4 and animation

Discussion about the development of the Assembly workbench.
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bestfit
Posts: 24
Joined: Wed Oct 10, 2018 5:37 pm

assembly 4 and animation

Post by bestfit »

Hello everyone!

I Have 3 parts:

1) One body blocked ; this body has an axle Z is the rotation axis
2) One arm which a hole this hole is centered on the body's axis allowing only a rotation between the arm and the body, this arm has also a prismatic section in order to guide a slider
3) One slider with the same prismatic section as the arm

I've placed LCS on each part, and I've "made" the connection between regarding LCS on both parts; and that"s working fine in a static way.

But my concern is when I try to animate all that.

I've tried to change the value of angle in the connection and it's working fine.... but I was excpecting the second relationship ( the slider relationship) not to move; And it does'nt work this way; when changoing the angle of the rotation, the positionment of the slider does"t stay on the arm.

What could happen? do I need to "block" the slider on the arm and to relax it after ( because of course, I want to move the slider when I've reached the good angle in the first movement...) and if yes, how to block? But probably , my issue is maybe due to the relative positionning of the LCS which could be perturbated by the rotation... Or maybe other thing...

if you have a solution or at least an indication on what could explain this behaviour , it will be an help for me.

Best regards,
Best Fit

Code: Select all

OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.1.29410 (Git)
Build type: Release
Branch: releases/FreeCAD-0-20
Hash: f5d13554ecc7a456fb6e970568ae5c74ba727563
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.3
Locale: French/France (fr_FR)
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ppemawm
Posts: 879
Joined: Fri May 17, 2013 3:54 pm
Location: Manhattan New York

Re: assembly 4 and animation

Post by ppemawm »

bestfit wrote: Thu Sep 22, 2022 9:56 pm if you have a solution or at least an indication on what could explain this behaviour
It is difficult to tell what your situation is without a file to study.
But, as a guess, experiment with the following:

1. Create a sketch in Model that follows the motion you want. If you can animate the sketch properly, you can animate the assembly.
2. Attach LCS to the sketch vertices or edges for each part
3. If you want a slider joint, make sure that one LCS axis is aligned (tangent) in the direction of the slider guide
4. Attach each of the body LCS to the proper LCS on the sketch.
"It is a poor workman who blames his tools..." ;)
bestfit
Posts: 24
Joined: Wed Oct 10, 2018 5:37 pm

Re: assembly 4 and animation

Post by bestfit »

Hi Ppemawn,
thank's for your advices! I thought that when creating a LCS in a body, it will keep the initial positionning design; in fact if its position is regarding one referentiel not attached to the part , it should be the cause of my issue... you're right. I just have to understand and to see how to attach the LCS to a straight line in my body...I probably will manage that after some tests!
Just a confirmation, to make a scketch is not mandatory, it's just to check ... right?
Best regards
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ppemawm
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Location: Manhattan New York

Re: assembly 4 and animation

Post by ppemawm »

bestfit wrote: Fri Sep 23, 2022 9:26 am Just a confirmation, to make a sketch is not mandatory, it's just to check ... right?
Without knowing what your exact configuration comprises, it may be that you do not need a sketch to solve for the positions as your animation variable changes. Remember that Assembly4 does not have an explicit assembly motion solver. It locks all degrees of freedom when you attach one LCS to another which can only be freed with Attachment Offset displacements or rotations and/or Expressions. If you cannot describe the motion mathematically in Expressions then your next best option is to use the Sketcher constraints and solver.

You may be able to attach to a body edge and align the LCS so that it will follow your motion but also be aware that it will be susceptible to the TPM problem if you modify any of the features. Sketches are less susceptible but not fool proof especially if the motion is over a large range.

See also this excellent tutorial by Zolko: https://github.com/Zolko-123/FreeCAD_Ex ... /README.md
"It is a poor workman who blames his tools..." ;)
bestfit
Posts: 24
Joined: Wed Oct 10, 2018 5:37 pm

Re: assembly 4 and animation

Post by bestfit »

Hi Ppemawn,

I think I've understood what you mean.
I've tried to attach the LCS to each body , but I"m not 100%sure doing the right way.I've attached a line linked to the slider, but the situation didn"t really change .
I've found a tutorial on the way to do that (https://wiki.freecadweb.org/PartDesign_CoordinateSystem) , but It seem's I don't catch the philosophy...
Do you know a better tutorial on that matter?

I didn't want to borrow you with my issue, knowing that I'd prefer to find the solution on my own; that's the reason why I didn't attached my files... If no solution on my side, I hope you can give me some more information on my system after seing it...but for the time being, I'd lke to solve the problem myself
Thank's for your help and for the time you spend on my issue
Best regards
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ppemawm
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Location: Manhattan New York

Re: assembly 4 and animation

Post by ppemawm »

bestfit wrote: Fri Sep 23, 2022 10:36 pm Do you know a better tutorial on that matter?
Your best bet is to stay in the Assembly4 workbench and use the provided LCS's via Create a Datum Object tool rather than PartDesign. The Assembly4 Part and Body also have default LCS's for use during assembly.

The most thorough discussion is here: https://wiki.freecadweb.org/Part_EditAttachment but not easily understood. My best advice is to follow all of Zolko's Assembly4 tutorials closely and experiment with the different attachment modes. You need to be able to reproduce Zolko's tutorials before trying anything different.

Same with this tutorial: https://wiki.freecadweb.org/Basic_Attachment_Tutorial
"It is a poor workman who blames his tools..." ;)
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