making a tetrahelix

making a tetrahelix

I'm new to Cheetah 3D. I want to make a tetrahelix chain of about 10 tetrahedra, and haven't the slightest idea where to start. I thought that joining separate tetrahedra would be the way, but I'm having trouble even lining them up. Any advice for a complete novice?

bjaulicino said:

I'm new to Cheetah 3D. I want to make a tetrahelix chain of about 10 tetrahedra, and haven't the slightest idea where to start. I thought that joining separate tetrahedra would be the way, but I'm having trouble even lining them up. Any advice for a complete novice?

Click to expand...

hi,
actually i dunno what a tetrahelix chain is, so my suggestion may be not fitting, but you could think of modeling an inner core from triangles from which the tetrahedra were to be extruded.

example:

- make cylinder with sufficient alignment of segments
- in polygon mode with none selected, choose tools / triangulate
- you could now already select all triangles you wanna keep, invert selection and delete (or do that later)
- extrude all selected triangles with group preservation unchecked
- now the extruded faces are selected, apply normal move til they meet in singular points
- optimize in order to weld those and to delete all unused points

Hi.
Not quite sure.
I started with a ten storey cube; 10 sections and 10.0 height.
Make editable and do zick-zack cuts with the scalpel tool.
Delete every horizontal edges and add a "twist modifier".

Cheers
Frank

Assuming this is what you're talking about:



Constructing one correctly is no simple matter as the angle of each tetrahedron relative to the next is an irrational number.

The math is discussed here in some detail, and there's enough information here to put together a polygonobject script:

http://www.rwgrayprojects.com/rbfnotes/helix/helix01.html

This does suggest a fairly simple way of putting one together using C3D's usual tools:

1) Construct a triangular cylinder with say 12 vertical slices of height 2.5. Make it editable. Delete all faces (leaving vertices).

2) Create a helix of around height 5, 2765 degrees or so, 24 sections.

3) Now try to get the two to match up so the helix is passing through the vertices.

4) Create the polygons manually until you've made a stackable unit.

5) Make an array of stackable units.

6) Apply a twist modifier to the whole thing until it looks about right.

This is a ridiculously hard thing to build given how simple it looks...

Podperson, you always come through. Amazing!

obviously i did not sufficient research about what a tetrahelix is, lol.
but at least i have learned now.
thanks pod !

now this is a task for topmod, where you can do it with one single tool, the stellate extrusion.
simply you choose the tetrahedron object, then the stellate extrusion tool, select one face, extrude, continue...
this could be done in cheetah as well when you manage to find the right quantize value, but each step needs normal scale plus optimize welding, so that's rather time consuming, though maybe ok if you want only ten elements and rather avoid to learn topmod.

:smile:

Then here´s another one:


Cheers
Frank

Tetrahelix construction

Thanks Archie, Frank and Podperson for the excellent suggestions! I'll post my results.

Hey Frank -- the way you extruded the helix is exactly what I wanted but couldn't figure out how to do (I just wanted the helix as a set of reference points, but your technique is better).

Topmod looks awesome -- downloading it now.

very cool stuff here, I enjoyed every post!

downloaded some times ago but still have to find the time to play with TopMod... it's definitely worth a try!

cheers,
Alessandro

Top Mod is awesome, no doubt.

It is a perfect complement to C3D, as it can make some amazing constructs with minimal effort.

Cheers, Chuck