Assembly 4 - Attach assembly sketch to a moving object

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alexanderthomas
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Joined: Wed Jan 19, 2022 1:34 pm

Assembly 4 - Attach assembly sketch to a moving object

Post by alexanderthomas »

Hello,

Thank you for this forum. I am using FreeCAD 0.19 with Assembly 4 to assemble several parts into a model.
The object I am building is basically a horizontal plate on which 3 bars are articulated.

In my model, I have 4 parts : the horizontal plate (Base_plate) and 3 articulated bars (Bar_1, Bar_2, Bar_3).

The movement of Bar_1, Bar_2 and Bar_3 is coordinated by a sketch ("bar_sketch", in the model), which contains 3 segments (which represent the 3 bars) in the XZ plane, on which 3 LCS are attached. The 3 bars are imported on those 3 LCS. The sketch acts like a solver. The angle of Bar_1 (versus horizontal) is controlled by a Variable ("bar_1_angle"), and the 2 others move consistently with this input angle. It works fine.
Base_part is supposed to move on the XY plane. I know how to do it, by creating a Variable "base_part_position" and using it in the x and y coordinates assembly properties of this part. It works fine, the plate moves in the XY plane.

But I would like Bar_1, Bar_2 and Bar_3 to move along Base_part, on which they should physically by attached. Therefore, I would like to map the "bar_sketch" on "Base_part", but I can't find how to do it. In the properties of bar_sketch, clicking on Attachment>Map Mode>[...], I selected a face of Base_part and tried the two proposed attachment modes (Plane face and Inertia 2-3), but in each case, the Sketch won't follow the Base_part when I animate my Variable "base_part_position".

Do you know how to do this, please? Any idea is welcome.

(The two movements (Base_part and bars) are not simultaneous and I do not intend to animate the two "Variables" simultaneously.)
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Zolko
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Re: Assembly 4 - Attach assembly sketch to a moving object

Post by Zolko »

alexanderthomas wrote: Wed Jan 19, 2022 2:39 pm Therefore, I would like to map the "bar_sketch" on "Base_part", but I can't find how to do it.
Use a master-sketch in the assembly's root, attach various LCS to it, and attach the base-plate and bar-sketches to these LCS.
try the Assembly4 workbench for FreCAD — tutorials here and here
alexanderthomas
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Joined: Wed Jan 19, 2022 1:34 pm

Re: Assembly 4 - Attach assembly sketch to a moving object

Post by alexanderthomas »

Thank you for your answer. You mean, attach the bar_sketch to an LCS? How can I possibly do that?
It seems that each time I try to attach a sketch to an LCS, FreeCAD doesn't like it. In my assembly, I only succeeded attaching a sketch to the face of an object, but the sketch doesn't move with the object when it's animated.
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Zolko
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Re: Assembly 4 - Attach assembly sketch to a moving object

Post by Zolko »

alexanderthomas wrote: Thu Jan 20, 2022 6:50 pm You mean, attach the bar_sketch to an LCS? How can I possibly do that?
This is basic FreeCAD stuff, not Asm4, Please experiment
try the Assembly4 workbench for FreCAD — tutorials here and here
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