I want to draw a 3D structure diagram of a new device.
Can you recommend a software to draw schematics like this one:
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This is a drawing of a 3D assembly with annotations- a simple one, but too complex to be drawn in a 2D flowchart and diagram making software. Illustrator, Inkscape, Affinity Designer or something comparable is needed. As suggested you can have an isometric or other projection grid to help to get the line directions right.
I do not recommend 2D approach. With a 3D drawing program you can get all watching directions with no extra effort. This doesn't need anything complex such as Blender, you can well use some entry level 3D modeller.
My old favorite is DesignSpark Mechanical. It has under the hood SpaceClaim, but as usually in freeware, many professional features are disabled. It can still make models which contain simple extrusions, revolved pieces, lofted surfaces and pipes where a profile is pulled along a curve. You can colorize the parts or export (=print as PDF) a wireframe with or without hidden lines. There's no photorealistic materials, only colors.
An example with few parts copied from your concept:
The program has so intuitive and flexible user interface that making this 3D model took only few minutes, it's faster than drawing it in 2D (except with pencil) and as said, one has all possible watching directions with the same effort.
This is what's got to Inkscape when the wirefame was printed as PDF, imported to Inkscape, applied Deep Ungroup to get all parts freely editable, all lines were set to the same color and thickness and a couple of random annotations were inserted:
It's a vector, so coloring the parts in Inkscape is theoretically possible. But PDF printing left the lines open and Inkscape hasn't well working Shape Builder like Illustrator, so coloring needs much of curve joining work and drawing missing sides. Coloring is possible much more easily by inserting the colored bitmap rendering under vector drawing (no colored 2D vector exports are possible in DS Mechanical). It looks still sharp due the sharp vector outlines: