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01-23-2014
10:08 AM

01-23-2014
10:08 AM

Logarithmic spiral in Creo 2.0

I am trying to create a **logarithmic spiral **defining it with an equation, but I can't get it to work!

I found a formula on another forum (for ProE) and copy/pasted it into the equation window.

theta = t * 360 * 2.2

a = 0.005

r = exp (a * theta)

The result is "Feature failed to regenerate". Creating ordinary spirals gives no problems, but adding ln, x^ or exp functions gives me problems. I think I miss some basic programming skills here.

Any suggestions how I get going?

Thanks, Jeppe.

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8 REPLIES 8

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01-23-2014
10:23 AM

01-23-2014
10:23 AM

Re: Logarithmic spiral in Creo 2.0

Going for the easy solution: Are you using a cylidrical coordinate system? If not then theta and r won't affect anything.

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01-23-2014
12:39 PM

01-23-2014
12:39 PM

Re: Logarithmic spiral in Creo 2.0

Well, I'm on WF5/creo, and I've never seen "a", for cylinderical, it's r, theta, and z, in that order.

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01-23-2014
12:51 PM

01-23-2014
12:51 PM

Re: Logarithmic spiral in Creo 2.0

In this case "a" is just a constant, though there should be a value set for "z"

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01-23-2014
02:18 PM

01-23-2014
02:18 PM

Re: Logarithmic spiral in Creo 2.0

The equations are parametric equations (mathematical definition), relating each of the variables r, theta, and z to the parameter t.

Vary t from 0 to 2 in the dashboard, change to a cylindrical coordinate system, choose your csys, and then enter the following equation:

r=exp(5*t)

theta=t*360*2.2

z=0

Change z to z=exp(5*t) to get a exponential helix. Be careful with exponentials. A little bit can go too far very quickly and it will fail.

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01-23-2014
02:35 PM

01-23-2014
02:35 PM

Re: Logarithmic spiral in Creo 2.0

If you use the above equation, zoom in an out, it's like watching the intro of an old Dr. Who show.

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01-23-2014
02:39 PM

01-23-2014
02:39 PM

Re: Logarithmic spiral in Creo 2.0

Good observation on the range of values.

The original radius is from 1 (exp(0)) to about 52.5 (exp(0.005*1*360*2.2))

Ever watch Doodling in Math Class with Vihart?

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01-23-2014
02:44 PM

01-23-2014
02:44 PM

Re: Logarithmic spiral in Creo 2.0

Yeah, funny stuff. If you watch closely, you can almost see the pencil shrinking through the videos.

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01-24-2014
02:47 AM

01-24-2014
02:47 AM

Re: Logarithmic spiral in Creo 2.0

It works:-) Thanks guys!

Jeppe

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