chrisb wrote: ↑Sat May 08, 2021 5:07 am
Is there a certain design goal behind the complicated sketch with all its triangles? Are there given design parameters?
See the product photo in my original post concerning what the triangles are. They are what hold the support points that make contact with the telescope mirror. The triangles pivot on a spherical bearing, and the bars that hold the triangles can also pivot. The overall design is what's called an "18 point mirror cell" and is standard practice for telescopes of the size I'm planning to build. The design parameters for the triangles come from specialized software called PLOP. It calculates the optimal placement of the mirror support points, as well as the triangle's pivot point, in order to minimize the deformation of the mirror under its own weight (at the sub-micron scale).
The positions of triangle's pivot points determine the placement of three of the frame pipes. Thus why there were so many triangles in my sketch. However, it turns out I didn't really need the triangles within the sketch of the support frame. The triangles are now in a separate sketch within what I call a "triangle plate" assembly.
There was another reason for all the triangles in the sketch, having to do with me with me wanting them equilateral, but PLOP doesn't generate equilateral triangles. I was relying on the sketch to make them equilateral. I've since changed my mind; they are no longer equilateral. You can read all the gory details about this here if you care to:
https://www.cloudynights.com/topic/7688 ... oint-cell/
I've since learned that calculating a bit of geometry within FreeCAD spreadsheets can remove a lot of construction lines in the sketch.
Here's my current simplified sketch without the triangles.
- SimplifiedSketch.png (56.25 KiB) Viewed 1836 times
My (incomplete) mirror support with the triangle sub-assemblies is coming along nicely, IMHO.
- MirrorSupport.png (65.15 KiB) Viewed 1836 times
If my telescope turns out to be successful, I might change my mind about sharing the CAD file. For now, I don't want to be blamed if others use this unproven design and it fails on them.