Logarithmic spiral in Creo 2.0

[ptc-5480261]

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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[dschenken]

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

[Patriot_1776]

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

[dschenken]

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

[neomechanikos]

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.

[neomechanikos]

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

[dschenken]

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?

[neomechanikos]

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

[ptc-5480261]

It works:-) Thanks guys!

Jeppe