Parametric equations

[itsme]

Hello everyone

I'm not very good with CAD software (yet!), because I'm very new to it.

I would like to be able to draw accurate curves from parametric equations, but I'm not even sure if any CAD products can do this. Are there any out there that can (and don't cost a fortune)?

Any help would be appreciated.

Thanks
Warren

[HuFlungDung]

Hi Warren,

Interesting question, I'd like to hear if there is anything like that, too, just for interest's sake.

However, I do know that equations most often give one (or two) different answers based on the actual variable input used. This means that the graph of the solution is based on discrete point sample solutions. For high accuracy, you use lots of points, for low accuracy, you use less.

So the way that this can be handled, (IMO) is with one of three different types of curves called splines. There are B-splines, Cubic splines and Bezier splines. Most CAD programs (I would guess) will allow you to "connect the dots" with one or more of these options. So, you have to work your equations for enough solutions to plot enough points for the accuracy you require. Then, the spline represents one of the reproducible methods of creating the best fitting curve.

[buscht]

itsme, I had an answer for you until you jinked it with that last statement, (and don't cost a fortune).

Parametrics can be expressed mathematically, so if you can write the math formulas you can put them into Excel and let it calculate starting and ending points, radii, etc.

This data can be manually drawn in any inexpensive CAD, or if you use AutoCad you can write a Visual Basic routine to draw the arcs for you using the Excel data.

You have to be pretty good at trig, and VB programming to do this.

[itsme]

Thanks for the replies,

If I left out the 'and don't cost a fortune' part, could you possibly give me that answer?

It also sounds interesting what you (buscht) had to say about using Excel, but I would like to know exactly whatI could do with the shape once it was in Excel, or is this just a method of graphing it?

Warren

[buscht]

Here's a company that sells an AutoCad solution.
http://www.synthesiscompany.com/asp/....asp?page=home
Of course, you'd have to ask if they can handle curves.

Solidworks or Pro Engineer are parametric driven CAD programs.

With respect to my Excel idea, I am only talking about curves (meaning arcs) not splines like HU is talking about. Anyway, if you have Excel and AutoCad, both can be controlled by Visual Basic macros. You can write these yourself. The macro can read the Excel data, interpret this data and draw the appropriate arcs in AutoCad.

Here's an example of an Excel VB macro that controls Autocad to draw an ARC. You need to know the center point, diameter, and starting and ending angles in order to automate drawing an ARC. Also, for some reason it works in radians, so there is some math in there to translate that.

With a little more work you can have the program fill in these values automatically from the spreadsheet.

Sub addARCROUTINE(x, y, DIA, STARTANGLE, ENDANGLE)
Set ac = GetObject(, "AutoCAD.Application")
Set objModelSpace = ac.ActiveDocument.ModelSpace()
Dim ARCObj As AcadArc
Dim centerPoint(0 To 2) As Double
centerPoint(0) = x: centerPoint(1) = y: centerPoint(2) = 0
Set ARCObj = objModelSpace.addARC(centerPoint, DIA / 2, STARTANGLE * 3.141592 / 180, _
ENDANGLE * 3.141592 / 180)

End Sub

Doing 2D work is pretty easy, 3D is way above my skills and I would recommend you talk to a Solidworks distributor to see if they can do what you want.

As a side note, I have seen some people skip the CAD step and go right from the Excel spreadsheet and generate G code. Afterall its all just numbers.

Good luck
Trent