Hope this helps.

The vertical cylinder where the ropes go around has a diamter of 0.25 and a
height from < 0.0, 0.0, 0.0 > to < 0.0, 2.7, 0.0 >.

The arm separates from the middle of the cylinder#s height and has an own radius
of 0.2 there.

Excerpt:

 union // sling arm
 {
  cylinder { < 0.0, -0.2, 0.0 > < 0.0, 2.5, 0.0 > 0.25 texture { TopColor rotate
< 90.0, 0.0, 0.0 > } }
  cone { < 0.0,  1.15,  3.0 > 0.15 < 0.0, 1.15, 0.0 > 0.2 texture { TopColor } }
  box { < 0.0, 1.00,  3.0 > < 0.18, 1.30,  2.5 > texture { RustyIron } }
  cylinder { < 0.0, 1.15,  3.0 > < 0.0, 1.15,  2.9 > 0.17 texture { RustyIron }
}
  cylinder { < 0.0, 1.15,  2.7 > < 0.0, 1.15,  2.6 > 0.18 texture { RustyIron }
}
  torus { 0.15, 0.05 translate < 0.18, 1.15,  2.75 > texture { RustyIron } }
  sphere { < 0.0, 1.15,  3.0 > 0.15 texture { RustyIron } }
  torus { 0.05, 0.025 rotate < 90.0, 0.0, 0.0 > translate < 0.33, 1.15,  2.75 >
texture { Rope } } //  // ropes around rings
  cylinder { < 0.33, 1.15,  2.75 > < 4.19, 1.275,  3.7825 > 0.025 texture { Rope
} }
  rotate < 0.0, 55.0, 0.0 >
  translate < -1.5, 0.0,  1.32 >
 }
The first cylinder is the vertical one (rope skein), and the first cone is the
arm.

The ropes need to have a cross-section radius larger tan 0.025, maybe 0.030 or
0.035 maximum.

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Examples...

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Attachments:
Download 'details - 001.jpg' (229 KB)

Preview of image 'details - 001.jpg'

So, basically you want something like this:

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Attachments:
Download 'romanballista.png' (67 KB)

Preview of image 'romanballista.png'

"Bald Eagle" <cre### [at] netscapenet> wrote:
> So, basically you want something like this:

Yes, to some extend, I like what I see. :-)

There are the ropes on the left side of the vertical cylinder, and those on the
right side. All twist around the horizontal arm. The ropes of the one side
(let's say left) are ABOVE the ropes of the right side.

Would you allow me to give you credit inside the scene file?

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"Sven Littkowski" <nomail@nomail> wrote:

> Yes, to some extend, I like what I see. :-)
>
> There are the ropes on the left side of the vertical cylinder, and those on the
> right side. All twist around the horizontal arm. The ropes of the one side
> (let's say left) are ABOVE the ropes of the right side.

So you just need to define a radius one rope diameter more for the second set in
order to arrange all the ropes the way you need them.

> Would you allow me to give you credit inside the scene file?
Sure thing - it's a lovely siege engine you've built.   :)

Let me know if you have any questions.

  #declare Ropes =
union {
#declare RopeR = 0.03;
#for (Y, 0, 2.5, 0.01)
 #local R = 0.25+RopeR;
 #switch (Y)
 #range (0.00, 0.95)
  #declare Theta = (Y/0.95)*pi;
  #declare X = R*sin(Theta+pi);
  #declare Z = R*cos(Theta+pi);
  sphere {<X, Y, Z> RopeR }
 #break
 #range (0.95, 1.35)
  #declare Theta = ((Y-0.95)/(1.35-0.95))*pi;
  #declare a = 0.2*0.2;
  //#declare X = 8*pow(a,3)/(pow(Y-1.15,2)+4*pow(a,2));
  #declare X = 0.1*sin (Theta);
  //#declare Z = -R;
  sphere {<X, Y, Z> RopeR }
 #break
 #range (1.35, 2.50)
  #declare Theta = ((Y-1.35)/(2.5-1.35))*pi;
  #declare X = R*sin(Theta+pi);
  #declare Z = R*cos(Theta);
  sphere {<X, Y, Z> RopeR }
 #break
 #end
#end
texture {Rope}
pigment {Green}
rotate y*25
}
#for (R, 0, 3)
 object {Ropes rotate y*R*10}
#end

    rotate < 0.0,180, 0.0 >
 }

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Working on the ballista in the meantime, removing errors and adding detail
features...

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Attachments:
Download 'sl - roman ballista 001.jpg' (676 KB)

Preview of image 'sl - roman ballista 001.jpg'

"Bald Eagle" <cre### [at] netscapenet> wrote:
>   #declare Ropes =
> union {
> #declare RopeR = 0.03;
> #for (Y, 0, 2.5, 0.01)
>  #local R = 0.25+RopeR;
>  #switch (Y)
>  #range (0.00, 0.95)
>   #declare Theta = (Y/0.95)*pi;
>   #declare X = R*sin(Theta+pi);
>   #declare Z = R*cos(Theta+pi);
>   sphere {<X, Y, Z> RopeR }
>  #break
>  #range (0.95, 1.35)
>   #declare Theta = ((Y-0.95)/(1.35-0.95))*pi;
>   #declare a = 0.2*0.2;
>   //#declare X = 8*pow(a,3)/(pow(Y-1.15,2)+4*pow(a,2));
>   #declare X = 0.1*sin (Theta);
>   //#declare Z = -R;
>   sphere {<X, Y, Z> RopeR }
>  #break
>  #range (1.35, 2.50)
>   #declare Theta = ((Y-1.35)/(2.5-1.35))*pi;
>   #declare X = R*sin(Theta+pi);
>   #declare Z = R*cos(Theta);
>   sphere {<X, Y, Z> RopeR }
>  #break
>  #end
> #end
> texture {Rope}
> pigment {Green}
> rotate y*25
> }
> #for (R, 0, 3)
>  object {Ropes rotate y*R*10}
> #end
>
>     rotate < 0.0,180, 0.0 >
>  }


Hi, thanks a lot! However, there is something missing from your code, it might
be something that would be above the "#declareRopes" statement at the very top.
The missing part would be on the same level like the "#for(R,0,3)" statement on
the bottom. can you check and add the missing code?

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"Sven Littkowski" <nomail@nomail> wrote:

> Hi, thanks a lot! However, there is something missing from your code, it might
> be something that would be above the "#declareRopes" statement at the very top.

Yep - sorry - that's just:

 union // sling arm
 {
  cylinder { < 0.0, -0.2, 0.0 > < 0.0, 2.5, 0.0 > 0.25 texture { TopColor rotate
< 90.0, 0.0, 0.0 > } }
  cone { < 0.0,  1.15,  3.0 > 0.015 < 0.0, 1.15, 0.0 > 0.2 texture { TopColor }
}
                              ^^^^^ note 1/10 of original just for demo purposes

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Big thanks once more - I am going to incorporate this into the file.

by the way, this here is not really a siege artillery, it is a naval artillery.
Was used on Roman battle galleys, thus the round platform which allowed to be
turned to all sides.

Siege artillery lacked that round platform as they were not needed to be
flexible, as fortresses not really moved around that much. :-)

Mounted on ships, during an ancient ship battle, the ships often changed
direction, sometimes quite abruptly, and so did their targets, too. Thus the
added flexibility of being able to turn around the Y axis.

For your pleasure, I am including now the latest version of the naval ballista.

3.65 MB

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Attachments:
Download 'ballista 001v2.rar.dat' (3758 KB)

This is the credit I am using, please let me know, if you're okay with that.

// Scene file developd by Sven Littkowski, C 2020.
// Credits for the twisted ropes go to BaldEagle
// a long-time member of the POV-Ray community.


Also adding the latest image.

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Attachments:
Download 'sl - roman ballista 001a.jpg' (930 KB)

Preview of image 'sl - roman ballista 001a.jpg'