[Howto]: Long size and double-scale Oloids

[Eric]

Here is my howto of the double-scale Oloid discussed in the Oloid thread in the 'Math-related Geomag discussions' forum.
Feel also free to take a look at my 'Oloid delirium' thread

Let's start.
First, I make 2 pentagonal bipyramids. The blue one is already finished on the photo below. Let's build the white one.

I thought I needed to reinforce the inner structure to help it keep its perfect shape of pentagonal bipyramid (did it in the blue one).

But I realized by testing it with the white one that it was not necessary. Once properly closed, the structure takes its shape, remains rigid and no longer deforms. So I removed the silver rods.

By connecting the free rods of the 1st photo to the corresponding spheres we give the concave shape to the double-scale pentagon

[Eric]

To build the other side of the pentagonal bipyramid, I make each double-scale triangle one by one (first the outer frame and then the small triangle for the inner structure).
As long as you have not placed the last double-scale triangle of the pentagonal bipyramid, the structure deforms and is not fully rigid.

Now we have our two pentagonal bipyramids that will collide

But first, let's do some digging:

We could build the double-scale oloid directly but I find it easier to build the two pentagonal bipyramids separately and then remove the excess rods

[Eric]

We have now to remove the 8 excess spheres to ensure the connection:

View from the side

It's a little scary from above, but everything will be fine

View from a higher point

All that remains is to carefully push them towards each other to fit them together.

What a great satisfaction when you hear and feel the clicks of the rods connecting to the spheres and the new structure finding its final rigid and strong shape!
Remember to check that the connections are firmly made on each sphere and adjust the rods if necessary.

Tada: Final assembly :-)

Final count:

• A pentagonal bipyramid is 60 rods and 22 spheres
• A double scale Oloid is 96 rods and 34 spheres (you'll need 120 rods and 44 spheres if you go through the 2 bipyramids step)

See more photos and also my "Yin and yang Oloid" in the Oloid Delirium thread.

[Eric]

Peter also challenged us for long size Oloids.
And I took up the challenge

Here's my howto for scale-1 long size oloid:

Add the edge rods only

Connect

Fill the gaps to form triangles et voilà :-)

If rods are to short to connect to certain spheres, don't panic, just squeeze a little the pentagonal bipyramids by their vertices and that should fix the problem.

[Eric]

Now the scale-1 extra long size Oloid:

Prepare only the edges that will connect the vertices

Connect and fill the gaps to form triangles

Tada!

Nice shots to see in the 'Oloid delirium' thread, with also the twisted Oloid and the angular Oloid

[Eric]

Let's go bigger now!
Here is how to build the double-scale long Oloid

First, split in half the double-scale Oloid that you took so long to build
Or start from two pentagonal bipyramids. As you wish.

It's a split!

Add spheres to the free rods and prepare the edges only.

I learned with the scale-1 long Oloid that it's easier to build the edges first and then fill the gaps.

Make the connection

[Eric]

Place the edges of the big triangular faces

Fill the gaps with small triangles

Admire your work

Nice shots in the 'Oloid delirium' thread

Let's talk about numbers for this big boy :

• We added 40 rods and 16 spheres to the normal size double-scale Ovoid
• So a long size double-scale Oloid is 136 rods and 50 spheres

[Eric]

(Links to photos restored in my posts)

[gmtrcply]

Peter also challenged us for long size Oloids.
And I took up the challenge
( ... )

If rods are to short to connect to certain spheres, don't panic, just squeeze a little the pentagonal bipyramids by their vertices and that should fix the problem.

I just tried the long oloid arrangements with short and long rods. Both show significant wiggle on the outermost shperes. Even when using 13mm spheres, there is a tiny amount of wiggle. So I think that 13.5mm is the safe sphere diameter for this arrangement. In about ten days I'll be able to tell for sure, some days ago I ordered 13.5mm spheres from China.

The manufacturers chose the acute angle of pentagonal bipyramids as design citeria, so you can't go much below that.