"Fixed Rotation" constrain on nested assembly

[cschwick]

Dear experts,

I try to build a 3D model of a room with racks and crates inside.

I started to build a simple 3d Model for a rack. It is an assembly of a handful of objects.

I then try to place these racks into a "room" which itself is an Assembly too. As long as I use fixed locations for the racks all works fine. Now I want to rotate the racks in every second row with the "Fixed Rotation" constraint. However, cadquery complains with

ValueError: Workplane or Shape is required to define a constrains.

May be I misunderstood but I thought it is "legal" to use assemblies to build bigger assemblies (the .add method accepts objects of type assembly, and works as expected)

Did I misunderstand? Is cadquery the wrong tool for what I want to achieve?

For completeness I attach 3 source files and a screenshot of the result when I do NOT use rotation. The code for rotating every second row of racks is commented out.

Thanks for any advice!
And of course: Thanks for this awesome project !!!!!!

[rack.py](https://github.com/user-attachments/files/25395401/rack.py) [floor1.py](https://github.com/user-attachments/files/25395403/floor1.py) [config.py](https://github.com/user-attachments/files/25395405/config.py)

[cschwick]

I answer my own question.
I found that the cq.Location object can also contain a rotation and with this I can achieve what I want.
Sorry for the spam... struggling still a bit with the documentation...

[adam-urbanczyk]

cq.Location represents a complete 6DOF (rotation + translation). There are many constructor overloads and you can combine locs using *.

With that being said, could you reshare your code or a MRE (the links do not work anymore)? I'd like to make sure if the original problem is not a bug.

[cschwick]

Dear Adam,

Thanks for following up. I simplified my code to demonstrate the problem/misunderstanding I had. In the attached tar you find all files to reproduce my problem. I use:

cadquery 2.6.1
cadquery-ocp 7.8.1.1.post1
cadquery_vtk 9.3.1

and cq-editor to show the results.

The file "racks.py" contains a class which builds a simple model of a rack.
It returns an "assembly".

The file racks_without_constraints_ok.py makes a nested assembly (an
assembly of racks) and rotates the racks with the loc parameter. This works.

The file racks_with_assemblies_bad.py makes a nested assembly and tries to
rotate the racks with constraints. This does NOT work.

The file racks_with_boxes_ok.py uses boxes instead of racks. Hence NO nested
assembly here. It uses the same constraints as in the example above and
here the rotation works.

I hope this helps... Probably the misunderstanding is on my side... (I am starting with cad-query (used OpenSCAD up to now))

Thanks a lot, CS

problem.zip

[adam-urbanczyk]

You have to reference nodes containing something (i.e. having non-empty obj field). The following snippet fixes the issue.

    fas.constrain( "rack1/structure@faces@<Z", "Fixed")
    fas.constrain( "rack2/structure@faces@<Z", "FixedPoint", (posx2,posy2,0))
    fas.constrain( "rack2/structure@faces@<Z", "FixedRotation", (0,0,45) )

[cschwick]

Thanks a lot Adam,

I understand better now.
I am still struggling with some fundamental concepts...
In particular I have not yet really understood what an Assembly is: it seems to be a "different animal" then a shape and your "path notation" seems to find the object in the assembly... I will play around further and search further the documentation...

Thanks again !