November, 2011 | CADD Edge Blog - Featuring SolidWorks 3D CAD Design Software

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How to Model an Epicycloid Curve in SolidWorks


Disclaimer:  This is probably my geekiest post to date.  There is a lot of math and my explanation of the theory is not likely to be entirely accurate.  You have been warned.

A question came up on the support line recently from a customer who was looking to model an

Epicycloid Curve.  We first had to learn what one was.  Wikipedia of course was there with the answer.  Basically its the curve produced when a point on one circle rolls along another circle. Think Spirograph.Spirograph via Wikipedia

Epicycloid Curve


The next challenge is creating the curve in SolidWorks.  Modelling a curve driven by an equation is actually quite easy.  Just start a new sketch and insert an equation driven curve.SolidWorks Equation Driven Curve

I chose to use the form of the equation.

Epicycloid Equation

Epicycloid equation

Which looked something like this where r =2 and k =1.  And we solve for the parameter t from 0 to 6.25 (approximately 2Pi)

blog epicyloid equationSolidWorks Epicycloid Curve

So that was easy now lets make some of the other cool shapes described on the wiki page.  I'd rather not dig through the equation each time I want to change a parameter and find each location, I'd rather make it parametric.  Currently it isn't possible to link an equation to a SolidWorks global variable, but I can link the variable to a sketch dimension.  So I added a couple sketch points and dimensioned between them and then linked them to my equation.

SolidWorks Parametric Equation

I have two dimensions in my sketch now, one called r, and the other called k.  By swapping "r@sketch1" and "k@sketch1" for the numbers representing those parameters I can now control the equation by modifying them or even linking them to SolidWorks Global Variables.

Its time to change k to 4 hit rebuild and get a cool shape like this one4 lobed epicycloid. My geometry didn't update at this point, how come?  The reason is that SolidWorks creates Equation Driven curves as splines.  A spline has to be continuous and smooth and the cusps or sharp corners cannot be drawn as a spline.  That is why I in my first exampe I stopped short of evaluating T all the way to 2Pi, I was cheating.  If we zoom in on my curve you'd see the shape isn't complete. If I want to depict the entire shape I can copy the curve four times and evaluate it for a segment representing each node.  Which looks like this. (Download here in 2011 format.)

What about all the other crazy ones?  Like this?   Can we do them?  Yes but we'll need Simulation Motion, Sketch Blocks, and Trace Paths.  I'll show you that in a future post.  For now here is a teaser video.



Taking SolidWorks Animations for a Spin


Being down at Foxwoods Casino for our User Conference must have inspired Jon S. from the New York office.  He created a great video showing you how to create an animation of a Roulette wheel using SolidWorks Simulation Motion.  Check it out, it shows how you can apply friction, motors and contacts using Simulation Motion which is part of SolidWorks Premium. 

SolidWorks Enterprise PDM Tech Tip #4


Lisa checks in with an overview of local views in EPDM.

SolidWorks Enterprise PDM Local File Vault View Overview

In order for any of the Windows Explorer-based SolidWorks Enterprise PDM clients to have access to a vault, the very first thing that must be done after the client installation is the creation of a local view of the vault or file vault view. The file vault view is directly connected to the archive server, which stores the physical files in a file vault archive, and the file vault database, which stores the information about files and activities in the file vault.

It is recommended that this file vault view, often referred to as "the blueberry" for the blue Enterprise PDM icon displayed for each file vault view, be located in the root of the local hard drive to make it easily accessible. See below for an example of a local file vault view:

blog epdm localview

The name of this vault, EPDM_Demo, is right next to the "blueberry". Notice that when the Folders option is used with Windows Explorer I can easily navigate through the file vault view on the left while seeing my file information on the right. The Windows Explorer view has the file information in the right top half with the columns having very useful PDM information such as Checked Out By, Description, Revision, State, etc. instead of the usual information in Windows Explorer like size of file and last modified date. The columns are configurable as to which properties are listed. The bottom right half displays the information about the file currently selected, a SolidWorks part, Arm.SldPrt, in this case.  

As you can see from the example above, the data card for the SolidWorks part file has been modified to use the SolidWorks logo. It is very easy to use your own company's logo instead, giving you a feeling of “ownership” to the software as it is implemented to work with your particular PDM needs.

 Speaking of data cards, stay tuned for the next SolidWorks Enterprise PDM Tech Tip!


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