topic Re: Parabolic Reflectors in AutoCAD Forum

Parabolic Reflectors

Anonymous — Tue, 21 Jun 2016 21:46:43 GMT

I am trying to make a solid that with a parabolic surface.

I plan to print a bunch or smallish parabolic surfaces with the intent of creating an array of parabolic mirrors to test the efficacy of a really inexpensive highly efficient solar heater. To do this I need to be able to vary the geometry of each parabola to have the axis and focus a bit different. I can create the mapping, the axis and focal point. What I can't seem to find is a means to create a square block with one side a parabolic surface in Autocad.

I understand the math but can't seem to figure out the mechanics of making it work with Autocad. I have Autocad Mechanical.

I will be grateful for any help.

Mike

Re: Parabolic Reflectors

SEANT61 — Wed, 22 Jun 2016 08:55:07 GMT

Perhaps this unit size paraboloid surface can be of use. With the proper scaling and CV manipulation, the surface can be tailored to size and focus - then used with the Slice command to shape a side of a Solid3d block. See attachment.

See manipulation in screencast:

Re: Parabolic Reflectors

Anonymous — Mon, 27 Jun 2016 14:04:25 GMT

Really neat!. I am sure it will do what I need.

I haven't worked with surfaces in Autocad so I have quite a bit to learn.

Thanks for your help!

Re: Parabolic Reflectors

SEANT61 — Tue, 28 Jun 2016 06:24:02 GMT

A surface is more easily manipulated. Eventually that surface can either be "Thicken"ed into a solid or used with the Slice command to carve a recession into a solid.

Re: Parabolic Reflectors

elshawadfy — Tue, 05 Jul 2016 06:04:09 GMT

Hi @Anonymous,

There are a lot of types of paraboloids.. If what you want is as @SEANT61 drawn, a circular base paraboloid cut to have a square base - not smoothly transitioning to the square base - then all you need is to create a parabola following your equation and revolve it , then intersect it with a box.. I Assume you need to follow specific equations for the parabola at least, so here is what you need:

1- Creating the parabola:

- You can use this lisp, and since you know the math - you can deduce the start, end, and the top vertex, which are what this lisp requires..

- The parabola base should be >= the diagonal of the square (equal to be start the paraboloid exactly from the square corner)

- The parabola height should be < the height used for intersection, to have the complete paraboloid..

2- Creating the circular paraboloid:

- Trim the curve to half.

- If you want the result to be a surface, Revolve the half curve directly 360 degrees..

- If you want the result to be a 3D Solid, Create a Region first between the half curve and straight lines, then Revolve the region 360 degrees..

3- 3DRotate the paraboloids to make them vertical

(Or you could have drawn the parabola in the front view in the first place - with UCS set to view of course)

4- Create a box,

- The sides of the box base are equal, and each is <= the paraboloid base /sqrt(2) (see the 1st condition of the parabola)

- The height of the box should be >= to the parabola or the paraboloid height

5- Move the box from center to the center of the bottom circle of the paraboloid..

6- Use "intersect" and select both the paraboloid and the box..

=================

If what you need is a soft transition to the square so that all points of the surface meet the square base - that's a very different story, it can be achieved easily in modeling - but the equations will be a hell to go through..

========================

Dwg Attached..

Regards..

Re: Parabolic Reflectors

SEANT61 — Tue, 05 Jul 2016 16:23:23 GMT

Nice work elshawadfy.

Now that this thread has come one more time, I realize the file attachment for my first post didn't make it online. May be late, but here it is anyway.

Re: Parabolic Reflectors

Anonymous — Wed, 06 Jul 2016 21:12:25 GMT

This is a real help.

I find the path from an idea to reality is strewn with shards of practicality.

An idea that stared on a bar napkin ( it really did) ended up with having to learn a lot of Autocad, the in's and outs of materials and 3D printing and the complexities of metal-plating of plastics.

I'm probably a few weeks to seeing first article. If it works, maybe I can make a gadget that will make power sufficiently cheap that folks in the bush can read at night. Maybe even make a phone call.

I thank you for your assistance.

Mike