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Re: [ATM] Help Examine the PLOP output
Hi George,
Thank you for the parameters - I'll computer them tonight as I'm
heading to an ATM session tonight, but let me first try and explain
the radius and angle parameters :)
The radius and angle of the center of gravity have the following
meaning: the traditional 18 points cell has 12 equidistant points on
one "outer" circle and 6 equidistant points on an "inner" circle. This
yields 6 identical triangles. The 6 triangles have their center of
gravity on another circle somewhere inbetween both previous circles.
That's the radius parameter that applies to the triangles. These 6
centers of gravity are also evenly spaced on that circle. The angle
parameter tells you where to position the first point with respect to
the horizontal X axis, and is measured counterclockwise (in degrees).
>From that first point's location (radius + angle from X axis) you can
derive the X and Y coordinates with simple trigonometric formulae: (x,
y) = (r cos a, r sin a) with r the radius of the CG and a the
starting angle of the first CG point on that circle. The other CG
points for the triangles are separated from each other by 360°/6 = 60°
(there are 6 triangles).
The same also holds for the levers. Each lever supports 2 triangles at
their respective centers of gravity. Inbetween both support points on
the lever lies the CG of the lever, exactly in the middle of both
support points. Due to symmetry the 3 levers are identical, and the 3
CGs are also spread evenly on another circle for which the radius and
starting angle are given in the "Part Dimensions" drawing for the
lever. The CGs of the 4 identical levers are separated from eachother
by 360°/3 = 120° (since there are 3 hinges).
In fact, the radius and angle parameter represent the location --
expressed in polar coordinates -- of the center of gravity of the
first element (lever or triangle) in a group of identical elements.
I hope this makes sense to you :)
Best regards,
Olivier
On 10/16/07, Geogre Nikolidakis <geoniko@otenet.gr> wrote:
> Hi
> I know you are wonderful people and I really thank you all
> For your intention to give me a help!.
> But my purpose when I started this project was to learn... -:)
> What is interesting in this project is the road on the trip and not
> Just only the destination.
> Olivier these are my mirrors parameters.
> Primary mirror diameter: 20" 508 mm
> Focal length : 90" 2286 mm
> Thickness of primary : 2" 50.8 mm
> Diameter of secondary : 4 " 101.6 mm
>
> Below are the results I managed to calculate with PLOP
> http://geonik.homeip.net/triangle.gif
> http://geonik.homeip.net/lever.gif
>
> But I still can't understand what it means with radius of CG and angle of CG
>
>
>
> Thanks
> George Nikolidakis
>
>
>
>
> -----Original Message-----
> From: Olivier Biot [mailto:olivier.biot@gmail.com]
> Sent: Tuesday, October 16, 2007 11:34 AM
> To: Geogre Nikolidakis
> Subject: Re: [ATM] Help Examine the PLOP output
>
> Hi George,
>
> CG is the abbreviation of Center of Gravity. that is the point where
> the triangles and bars have to be supported. The 18 points cell is
> symmetric in that it conisists of 3 identical pairs of 2 triangles
> supported in their center of gravity by a lever.
>
> What is most important for you is to know the center of gravity of the
> 3 levers, then the distance between the center of gravity of a lever
> (in other words: its middle) and the point where a triangle is
> supported.
>
> If you send me the specs of your mirror I will compute a cell for you
> and provide you all the needed dimensions.
>
> Cheers,
>
> Olivier
>
> On 10/16/07, Geogre Nikolidakis <geoniko@otenet.gr> wrote:
> > Hi all
> >
> > I am trying to design an 18 point mirror cell using the PLOP
> >
> > I thing at least I managed to have some reliable (?) output and
> >
> > PLOP gives me an output for the triangle and bars.
> >
> > I can understand the numbers in the corners and how they refers in a two
> > axis system
> >
> > In order to cut the triangles and bars..
> >
> > But I can't examine how I will position these parts relative to the
> mirror.
> >
> > The print parts says "Position of the CG of the parts relative to the
> center
> > of the mirror"
> >
> > And then gives some values X of CG, Y of CG, Radius of CG and Angle of
> CG..
> >
> > I am sorry but I am confused about what CG and all these numbers means
> !!.
> >
> > Any help it will be very appreciated!!
> >
> > Thanks in advance.
> >
> > George Nikolidakis
> >
> >
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >
>
>
>
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