I have a gear creation include file that i'm trying to make do bevel
gears, the trouble is that when ever i make the points for a conic_sweep
prism, they seem to be scaled to be slightly bigger(1.1?) in x/z... this
trouble doesn't exist when i'm making a linear_sweep of the exact same
values... is there some settings or an error that isn't documented? or
does anyone have the scale factor?

If there is alot of interest in this code, i might release it... but i'm
not sure yet...

also... has anybody made a rope include file that can make a sertain
length of rope between two points that are not level?
I have all the math, but can't seem to solve it...
(anybody know how to solve n=sinh(z)/z for z?)

     the Loial Raven, Matthew Peters

Post a reply to this message

Stuart Meerkat wrote:

> I have a gear creation include file that i'm trying to make do bevel
> gears, the trouble is that when ever i make the points for a conic_sweep
> prism, they seem to be scaled to be slightly bigger(1.1?) in x/z... this
> trouble doesn't exist when i'm making a linear_sweep of the exact same
> values... is there some settings or an error that isn't documented? or
> does anyone have the scale factor?
>
> If there is alot of interest in this code, i might release it... but i'm
> not sure yet...
>
> also... has anybody made a rope include file that can make a sertain
> length of rope between two points that are not level?
> I have all the math, but can't seem to solve it...
> (anybody know how to solve n=sinh(z)/z for z?)
>
>      the Loial Raven, Matthew Peters

Oh... i'm using a friends computer, so don't e-mail to the above address
my address is  Loi### [at] yahoocom

Post a reply to this message

Stuart Meerkat wrote:

> also... has anybody made a rope include file that can make a sertain
> length of rope between two points that are not level?
> I have all the math, but can't seem to solve it...
> (anybody know how to solve n=sinh(z)/z for z?)
> 
>      the Loial Raven, Matthew Peters

I believe there is a rope example that come with Chris Colefax's spline
include file which boasts the ability to make hanging/dropping chains,
ropes, etc.

http://www.geocities.com/SiliconValley/Lakes/1434/

-- 
Ken Tyler

mailto://tylereng@pacbell.net

Post a reply to this message

I think that it doesn't have the length variable, instead it has a variable
called a... you need to solve a whole bunch of stuff to get that though...


Ken wrote:

> Stuart Meerkat wrote:
>
> > also... has anybody made a rope include file that can make a sertain
> > length of rope between two points that are not level?
> > I have all the math, but can't seem to solve it...
> > (anybody know how to solve n=sinh(z)/z for z?)
> >
> >      the Loial Raven, Matthew Peters
>
> I believe there is a rope example that come with Chris Colefax's spline
> include file which boasts the ability to make hanging/dropping chains,
> ropes, etc.
>
> http://www.geocities.com/SiliconValley/Lakes/1434/
>
> --
> Ken Tyler
>
> mailto://tylereng@pacbell.net

Post a reply to this message

Matthew Peters wrote:
> 
> I have a gear creation include file that i'm trying to make do bevel
> gears, the trouble is that when ever i make the points for a conic_sweep
> prism, they seem to be scaled to be slightly bigger(1.1?) in x/z... this
> trouble doesn't exist when i'm making a linear_sweep of the exact same
> values... is there some settings or an error that isn't documented? or
> does anyone have the scale factor?
> 
> If there is alot of interest in this code, i might release it... but i'm
> not sure yet...
> 
> also... has anybody made a rope include file that can make a sertain
> length of rope between two points that are not level?
> I have all the math, but can't seem to solve it...
> (anybody know how to solve n=sinh(z)/z for z?)

What size are your gears?  I've just run a quick test using circular
points with a radius of around 1 unit, and both the linear and conic
sweeps are equal sizes in all dimensions.  However, problems with very
small object co-ordinates have been reported in the past...

As for the hanging cable question, I have to admit I've also been unable
to discover the answer (analytically, at least).  Therefore, at the
moment I can see two possible solutions: using approximation to find the
necessary 'droop factor' to give a desired catenary-segment length
(within a certain tolerance) or simulating the cable as a series of
linked springs.

The first option is probably quite feasible under POV-Ray 3.1 - I've
just created macros to reparameterize cubic splines by arc-length
(allowing constant length along the spline path regardless of shape),
and the sampling/interpolation performance seems to be quite acceptable
(and far faster than would have been possible under POV-Ray 3.0).

The second option (similar to the spring simulations described so
excellently by Hugo Elias) would also allow simulating cables with only
one end fixed (swinging pony-tails, etc.), variable masses along the
cable (eg. a necklace with a heavy pendant), and more.

I hope to be testing both methods soon, so that I can release a properly
updated version of my Link include file.  Some have suggested including
this as a feature of the POV-Ray Spline System I am working on at the
moment (so splines could have gravity forces applied to them), and it
might even be an idea to get both methods up and running...

Post a reply to this message

Just been having a look at your problem, of shin(z)/z=n, lets re-arrange
this to:
shin(z)=nz.

I'm assuming n is an integer, in which case I'm pretty sure therre will
be 2 roots. One will be pretty small <1, for n being reasonably high. 
In which case we can use the Taylor series expansion.  The other root we
won't be able to use the series, as it is non-convergent.  the problem
is, unless n is really small, we'll have to carry a lot of the tS to get
a reasonable answer, if n > 100 it should be OK (and we'd just need the
first 3 terms), but otherwise we'll have to solve the TS numerically,
I'd recommend bisection as I'm not sure Newton will work (but I always
use bisection - don't like the idea of a series which might not converge
- I'd prefer to guarantee it works and use a little more processor).  If
you have no idea about what I'm talking about, just email and I'll
explain further.

The Taylor Series is by the way :
  shin(z)/z= 1 + z^2/3! + z^4/5! ..... z^n/(n+1)!


So if we take the first four terms and then sub into the quadratic
formulae, we should get the answer for Z^2, root that and we would get
an answer, which for n>100 would be about 10^-5 accurate.  This is all
very roughly estimated, BTW.

Post a reply to this message

here is the test that shows the error... please could someone help, i've
already renamed all my variables and tried almost every aproach i can think
of... well, there was one thing left that i think might cause it... but i
have no clue of why sine and cosine would be redefined only when in
conic_sweep prisms... hmm...

well, here it is...

hope this works... ah well, have fun all :)
    the Loial Raven

Post a reply to this message

Attachments:
Download 'test.pov.txt' (10 KB)

oh ya, my addy is still different... should be fixed now...

Stuart Meerkat wrote:

> here is the test that shows the error... please could someone help, i've
> already renamed all my variables and tried almost every aproach i can think
> of... well, there was one thing left that i think might cause it... but i
> have no clue of why sine and cosine would be redefined only when in
> conic_sweep prisms... hmm...
>
> well, here it is...
>
> hope this works... ah well, have fun all :)
>     the Loial Raven
>
>   ------------------------------------------------------------------------
>
>                   Name: test.pov
>    test.pov       Type: POV-Ray scene file
(application/x-unknown-content-type-POV-Ray.Scene)
>               Encoding: base64

Post a reply to this message

Matthew Peters wrote:
> 
> here is the test that shows the error... please could someone help, i've
> already renamed all my variables and tried almost every aproach i can think
> of... well, there was one thing left that i think might cause it... but i
> have no clue of why sine and cosine would be redefined only when in
> conic_sweep prisms... hmm...

It took a while to 'decode' your code, but I think your problem is a lot
simpler than you think - the height of your prism (fake_th) is greater
than 1, therefore the conic_sweep extends out beyond the linear sweep. 
If you replace the fake_th with 1, you'll get prisms of exactly the same
dimensions.  If you want to create bevelled gears, it might be easiest
to create the top bevel prism from -1 to (-1 + bevel_height), and then
translate it up (+y) to sit on top of your linear prism.  The bottom
bevel could be the same object scaled by <1, -1, 1> or created at (1 -
bevel height) to 1, and translated down (-y).

Post a reply to this message

AHA!!! conic sweep prisms are drawn on the y*1 plane and then extruded past
there!!!... that's all my problems, so... if i am right, then i can just scale
the conic prism to the right length...

Let me go check... hehehe...
Thanks for all the help :)

Post a reply to this message