oblate geodesic dome, icosa 5v

[biagiodicarlo]

Dear Taff,

my next  project will be about a 15m oblate geodesic dome icosa 5v.

The diameter of the rods will be of 5 cm.

Please can you publish the  SUp drawings  similar to  'Oblate spheroid dome, 

Icosahedron tessellation: Class I, method 1 • Frequency: 4v • Vertical (z) scale factor: 0.618’ ?

If you can with peel pattern and chord  factors. 

Best regards,

Biagio

[TaffGoch]

Biagio,

This is 8/15ths ground truncation. (I wasn't sure whether you wanted 7/15ths or 8/15ths.)

The bottom two rows of "horizontal" struts initially traced a sinusoidal path, which I leveled to provide a flat footprint (making the bottom row of equal isosceles triangles.)

Is this configuration adequate to your needs (before I proceed further?)

-Taff

[biagiodicarlo]

Yes, this is the right configuration.

I will wait for the Shetch Up file.

Thank you very much !

- Biagio

Il giorno 04/ott/2015, alle ore 03:20, TaffGoch <taff...@gmail.com> ha scritto:

Biagio,

This is 8/15ths ground truncation. (I wasn't sure whether you wanted 7/15ths or 8/15ths.)

<Oblate; 5v.png>

The bottom two rows of "horizontal" struts initially traced a sinusoidal path, which I leveled to provide a flat footprint (making the bottom row of equal isosceles triangles.)

Is this configuration adequate to your needs (before I proceed further?)

-Taff

--
--
You received this message because you are subscribed to the "Geodesic Help" Google Group
--
To unsubscribe from this group, send email to GeodesicHelp...@googlegroups.com
--
To post to this group, send email to geodes...@googlegroups.com
--
For more options, visit http://groups.google.com/group/geodesichelp?hl=en

---
You received this message because you are subscribed to the Google Groups "Geodesic Help Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to geodesichelp...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[TaffGoch]

Biagio,

I labored to "normal" the struts, somewhat, to produce more uniformity in the lengths of all struts:

I prefer the above (B) design, as distribution looks to be more regular, with less of a "squashed" appearance to the lower tier of triangles. I assume that you would want to pursue the above (B) layout, rather than the previously-posted (A) design:

(... and the pentagon, at the top, is rather large in the (A) layout, increasing the chance of it "dimpling" inwards, under load.)

Comparison of the two layouts, A & B:

Your preference, A or B?

-Taff

[biagiodicarlo]

From my point of view this is the best form:

Thank you very much Taff, great geodesic helper!

-Biagio

Il giorno 05/ott/2015, alle ore 02:42, TaffGoch <taff...@gmail.com> ha scritto:

Biagio,

I labored to "normal" the struts, somewhat, to produce more uniformity in the lengths of all struts:

<Oblate 5v B.png>

I prefer the above (B) design, as distribution looks to be more regular, with less of a "squashed" appearance to the lower tier of triangles. I assume that you would want to pursue the above (B) layout, rather than the previously-posted (A) design:

<Oblate 5v A.png>

(... and the pentagon, at the top, is rather large in the (A) layout, increasing the chance of it "dimpling" inwards, under load.)

Comparison of the two layouts, A & B:

<Oblate-5v.gif>

Your preference, A or B?

-Taff

[TaffGoch]

Biagio,

I'm getting there....

You should note that the top 20 triangles of the dome approach being flat. If you are going to be building a tube frame, the fit of the topmost hubs/bolts must be carefully fabricated to close, tight tolerance. There shouldn't be any looseness or free-play in the assembly. Holes for the bolts should be a tight fit to the bolts. (The remainder of the frame shouldn't require such "tight" attention.)

I'm currently working on the chord diagram.

-Taff

[Gerry in Quebec]

Biagio & Taff,
For a tube-strut dome in which the strut ends are flattened and then bolted together, you may need to take into account the "twist angle" or "torque angle" of the oblique struts. We discussed this in 2012.

 

https://groups.google.com/forum/#!searchin/geodesichelp/Strut-twist$20angle

 

For many struts, the twist angle will be very small and can probably be ignored. But in some cases, I'm guessing it could be large enough to cause assembly problems if it is not accommodated when the strut ends are being flattened. There is also the issue of differing axial angles. For most of the struts in an oblate dome, the axial angle at one end of a strut will differ from the angle at the other end.

- Gerry in Québec

[Hector Alfredo Hernández Hdez.]

Twints angle increase like factor chord...

--

[biagiodicarlo]

Taff,

starting from your project I will translate it in 

a bamboo  reciprocal frame oblate geodesic dome.

Now I am waiting for  the chord diagram and SUp file. 

Again, thank you very much!

- Biagio

Il giorno 06/ott/2015, alle ore 05:36, TaffGoch <taff...@gmail.com> ha scritto:

Biagio,

I'm getting there....

<Oblate 5v Template.png>

You should note that the top 20 triangles of the dome approach being flat. If you are going to be building a tube frame, the fit of the topmost hubs/bolts must be carefully fabricated to close, tight tolerance. There shouldn't be any looseness or free-play in the assembly. Holes for the bolts should be a tight fit to the bolts. (The remainder of the frame shouldn't require such "tight" attention.)

I'm currently working on the chord diagram.

-Taff

[Gerry in Quebec]

Yes. If I have understood you correctly, the greater the chord factor, the greater the twist angle for oblique struts.

- Gerry

[TaffGoch]

So, Biagio,...

... you don't actually need the chord factor numbers?  This image maps the symmetry and repetition of chords:

Is this sufficient for the chords?

The model, currently, includes the dome shell, the colored chord diagram, and the unfolded template (for a paper model.)

If this is sufficient, the SketchUp model is done.

-Taff

[TaffGoch]

Biagio,

I mistakenly used the same color for two different chords. Here's the corrected diagram:

The corrected 3D model is attached.

-Taff

[biagiodicarlo]

Dear Taff,

you did a very great job, as always! 

I'd like to break off the dome in a plane, at the points where rest the bese pentagons. 

In such  way I can get a height even lower and I would say ideal for be reached with a chair or a small scale. 

Please can you level again in this way?

About CFnumbers, I  would like to get it.  

Maybe I can use the tape measure for this?

Best regards,

- Biagio

Il giorno 07/ott/2015, alle ore 06:38, TaffGoch <taff...@gmail.com> ha scritto:

So, Biagio,...

... you don't actually need the chord factor numbers?  This image maps the symmetry and repetition of chords:

<Oblate 5v chords.png>

Is this sufficient for the chords?

The model, currently, includes the dome shell, the colored chord diagram, and the unfolded template (for a paper model.)

If this is sufficient, the SketchUp model is done.

-Taff

-- 
-- 
You received this message because you are subscribed to the "Geodesic Help" Google Group
--
To unsubscribe from this group, send email to GeodesicHelp...@googlegroups.com
--
To post to this group, send email to geodes...@googlegroups.com
--
For more options, visit http://groups.google.com/group/geodesichelp?hl=en

--- 
You received this message because you are subscribed to the Google Groups "Geodesic Help Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to geodesichelp...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

<Oblate 5v B.skp>

[TaffGoch]

Biagio,

Yes, the tape measure (or even the line tool) can be used to display the lengths of chords.

Truncating, at the "pent base" level, removes much of the oblate appearance:

Is this what you want?

-Taff

[biagiodicarlo]

Yes, this is the form. 

I would like to lower all the base perimeter in order  to create triangular entrances suitable for an average person 

(such as the black triangle of my enclosed drawing). 

It's possible?

Il giorno 08/ott/2015, alle ore 04:16, TaffGoch <taff...@gmail.com> ha scritto:

Biagio,

Yes, the tape measure (or even the line tool) can be used to display the lengths of chords.

Truncating, at the "pent base" level, removes much of the oblate appearance:

<Oblate 5v truncation.png>

Is this what you want?

-Taff

[TaffGoch]

Gerry,

I found, while "framing" the subject oblate shell, that the aforementioned "twist" can be avoided, entirely:

Each of the "struts" is perfectly flat, with no angular discrepancy, end-to-end. I produced the struts by centrally scaling one oblate shell within another (95%.) My reasoning was that this would produce precisely-parallel strut edge-lengths. These edges, along with the end (hub centerline) edges being drawn-in manually, produced the struts, automatically "filled-in." (SketchUp will not fill-in a face if the polygon edges are not precisely planar.)

So, any position that I have previously-presented as fact, regarding end-to-end twist, I hereby withdraw. I have graphically-demonstrated, to my satisfaction, that twist does not complicate construction, if care is taken to properly design & model the oblate shell.

(Note, readers, that the hub centerlines still do not "point at" the central point of the oblate, as they would for a sphere. That characteristic can not be avoided.)

-Taff

[TaffGoch]

Ha!  Wrong again! 

The hub centerlines DO point at the center of the oblate. When I wrote the previous "fact," it gnawed at the back of my mind. I double-checked the model, and refuted my contention.

Note: This means that the plane of each strut also intersects the center point. This should certainly make dihedral measurements and cutting much easier.

-Taff

[TaffGoch]

biagiodicarlo wrote:

I would like to lower all the base perimeter in order  to create triangular entrances suitable for an average person

(such as the black triangle of my enclosed drawing)

It's possible?

Well, it's certainly possible, but would, in essence, require starting all over again, with new critera....

-Taff

[biagiodicarlo]

For the  entrances  I will work on the RF model.

Please can I receive the SUp file of the last drawing?

Thank you very much for all !

- Biagio

[Gerry in Quebec]

Taff,
The configuration you posted, using one central reference point, is what I used when I first started fooling around with ellipsoidal dome layouts several years back. (I've never built an ellipsoidal dome, just a paper model based on one of your earlier SketchUp models.) But this approach seemed, at least in theory, to result in misalignment of struts and panels in certain kinds of hub-&-strut domes, particularly pipe-strut domes where strut ends are squashed, bent and bolted together (drawing attached), like some of Blair's domes. So I started experimenting with multiple reference points so that each bolt or cylindrical hub would be perpendicular to the tangential plane at that particular vertex. But as you know, this requires some of the oblique pipe struts to be rotated by a certain twist or torque angle after one end of the strut is squashed but before the second end is squashed. It's a lot of extra work, especially in a dome that already has many chord lengths (e.g., 26 in your original model of the 5v icosa, 8/15ths oblate dome) compared with a spherical dome.

The use of a single reference point to eliminate the twist angle problem should work fine for hubless domes like the one shown in your screenshot of the SketchUp model. But there will be a heck of a lot of different compound angles to cut. This is true of both the arrowhead method and the Pease panel method. As you probably know, the late John W. Rich of New Zealand, who built a number of ellipsoidal dome homes, got around some of these problems by building triangular panels with vertical sides. These were bolted together into the oblate shape, and then the dihedral gaps were filled in with rough-cut wedge fillets of various thicknesses. (I'm told that, during construction of some of Rich's domes, workers up on the frame would call down to the ground crew, "We need a thickie", or "We need a thinny".)

One issue for Biagio is whether the use of a single, central reference point for establishing the strut dimensions will create any strut- or panel-alignment problems for the particular hub-&-strut system he's chosen. Or, will he need to custom-design the hubs?

- Gerry in Québec

[biagiodicarlo]

Gerry,

as I had already written 

for this dome I will use a reciprocal frame joint

and not a punctual joint.

In this joint the rods adapt themselves.

- Biagio

--
--
You received this message because you are subscribed to the "Geodesic Help" Google Group
--
To unsubscribe from this group, send email to GeodesicHelp...@googlegroups.com
--
To post to this group, send email to geodes...@googlegroups.com
--
For more options, visit http://groups.google.com/group/geodesichelp?hl=en

---
You received this message because you are subscribed to the Google Groups "Geodesic Help Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to geodesichelp...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

<Component-Alignment-Oblate-Dome.jpg>

[Gerry in Quebec]

Yes. Thanks for the correction, Biagio.

- Gerry

[TaffGoch]

Biagio,

Would this be of any help?

-Taff

[TaffGoch]

Gerry,

Regardless of the number of chord factors, I like the look of the (somewhat) "equalized" chords of these oblate spheres:

-Taff

[TaffGoch]

Biagio,

Attached SketchUp model:

[biagiodicarlo]

YES,

this is the dome.

-Biagio

Il giorno 13/ott/2015, alle ore 07:21, TaffGoch <taff...@gmail.com> ha scritto:

Biagio,

Would this be of any help?

<5v Drape.png>

-Taff

[TaffGoch]

Biagio,

See attached "Drape" version.

-Taff

[biagiodicarlo]

A very great design!

Thank you very much Taff.

-Biagio

-- 
-- 
You received this message because you are subscribed to the "Geodesic Help" Google Group
--
To unsubscribe from this group, send email to GeodesicHelp...@googlegroups.com
--
To post to this group, send email to geodes...@googlegroups.com
--
For more options, visit http://groups.google.com/group/geodesichelp?hl=en

--- 
You received this message because you are subscribed to the Google Groups "Geodesic Help Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to geodesichelp...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

<5v Drape.skp>

[TaffGoch]

I hesitate to tackle a 4v oblate reciprocal frame, due to the number of elements, but I did try a 3v (just to prove that I could do it.)

Here's the first draft...

...and it was more work than I'd like to admit!

I don't relish the idea of doing it again, even though it was an interesting exercise. Further attempts would be more like "work," rather than "testing" my SketchUp abilities/skills.

-Taff

[Sean T]

Hello Taff,

So I'm working on a project that will incorporate a 48' diameter oblate geodesic dome.  This will be my first attempt at a dome of any kind.  The dome will be constructed of EMT 3/4" conduit with flatten, bolted ends.  It will be used indoors, for projection on the domes interior surface, the liner will be made from ripstop nylon.  The model you've developed here seems to be perfect for my purposes, I've scaled it up and can find the strut lengths from the SketchUp model, but I was wondering if you can tell me how to easily find the angles the ends should be bent to?  I'm a beginner at SketchUp, so I'm not sure if there is an easy way to find the info there.

Any help would be greatly appreciated, this forum is an amazing reference and has helped me tremendously on this project, thank you so much for all your time!

Sean