Figure-8 Helix 2

[dakeb]

Hi guys,

Is it possible to do a helical type sweep, but in a figure-8 format?

e.g. imagine a spring wound in a figure-8 style, around two parallel mandrels?

cheers,

Dave

 

[grimmy65]

Something very similar was answered just days ago. Next time do a search before you post, as the policies of this forum state.

http://www.eng-tips.com/viewthread.cfm?qid=278385&page=1

 

[mjcole]

Figure 8 is not the same as square helix.

Curve by Equation can do this. It just depends on how exact you want your circles or if you want exact radii or not.

/* Equation Data
R=5
x=R*sin(20*t*360)
y=t*40
z=2*R*cos(10*t*360)

I will look and see if another method works better.
You may want to try using relations with a variable like(-1)^n to alternate positive and negative values for x to go positive and negative with absolute value between 0 and the Helix diameter or G=1-cos(value) which would have a range of (0-2)

Michael

 

[dakeb]

Michael,

Been unable to login to eng-tips for a few weeks. Thank you very much for your response, it was most helpful.

David

 

[dakeb]

This is actually a loop of thick cable stowed on arms protruding from some sub-sea equipment.

I modified the equations a bit to include editable parameters (number of coils, aspect ratio, cable diameter) and to make the cable touch at the cross-over point: -

x=RADIUS*sin(COILS*2*t*360)
y=t*COILS*CABLE_DIA*50
z=ASPECT*RADIUS*cos(COILS*t*360)

 

[dakeb]

Works better liek this for models in mm:-

x=RADIUS*sin(COILS*2*t*360)
y=t*COILS*CABLE_DIA*2
z=ASPECT*RADIUS*cos(COILS*t*360)

 

[dakeb]

I am still struggling. Turns out I really need a full-circle figure-8, i.e. two touching circles side by side looking in plan. No matter how I manipulate the above equation I cannot get a constant radius throughout the curve.

Any ideas anyone?

 

[mjcole]

The ideal answer would invole PTC adding the ability to use If relations in Equation curves like in Variable section Sweeps. Enter an If t>.3 statement in the relation editor and have ProE shake it's finger at you. I think a better method would be to enter the equations once and comment them out or use an evalgraph feature which I'm trying out.The other method would be to use an S shape and do 2 halfs of the figure 8 and possibly pattern with an offset Plane and Offset angle to achieve an easy to modify shape.

Dave told me he was using Wildfire 3 so I went ahead and created a trailfile which i will upload here as well

Michael

 

[dakeb]

SOLVED

r=500
d=65
x=2*r*cos(360*t)*sqrt(cos(360*t)^2)
y=2*r*cos(360*t)*sin(360*t)
z=t*d

Excellent work bronsona from the MathCad forum!!

Thanks

Dave

 

[dakeb]

Here is the part.

Thanks to all for your efforts in solving this. It was realy doing my head in, I knew it must be possible to do this with a single equation.

Dave

 

[dakeb]

Slight problem with the model, I cannot pattern from the diameter section location of the vss, it drifts off the z axis. Easily fixed, I set up a new offset csys for the curve and patterned that instead.

 

[dakeb]

In actual fact, I can do this without patterning at all, by having a continuous curve of 'n' coils, represented by: -

n=coils
r=radius
d=diameter
x=2*r*cos(n*360*t)*sqrt(cos(n*360*t)^2)
y=2*r*cos(n*360*t)*sin(n*360*t)
z=t*d*2*n

I can even have the half coil, e.g parameter: coils = 4.5, to make the cable terminate at the opposite end to the start.

Sweet!