Helix with variable pitch and radius

[vbmec2007]

I need to construct an electric heater coil using the helix feature. The problem is that I'm not able to create an helix with both variable radius and pitch. Any idea?

 

[hudson888]

You can create a helix curve with a variable radius using the helical curve creation tool. You create a tapered helix per normal except that for the radius method select use law and input the top and bottom radii. The easiest way is if you place the WCSYS at one end of helix with the Z-axis pointing along the intended axis.

You will find that there are several types of functions that you can use to vary the radii. You also can increase and decrease the radii top to bottom making a barrel shaped spring if you wish.

There does not appear to be any way in the helix curve function to vary the pitch. The closest I've been able to get is to create the helix in several segments, it is an approximation at best.

Hope this helps

Regards

Hudson

 

[vbmec2007]

Thank you very much Hud,

I've already tried to follow your tips but I have to control the pitch. For instance in Pro/E you are able to define a law curve for the pitch. Is there anything in NX that let me have the control of variable parameters of pitch and radius (any expression of helix by law?)

Thanks

Simon

 

[basenxuser]

Hi,

Use law curve by equation option with the following expressions.

For normal helix
t = 1
teta = 360
radius = 12
no_turns = 5
height = 45
pitch = ( height/no_turns )
xt = radius * cos( teta * t * no_turns )
yt = radius * sin( teta * t * no_turns )
zt = pitch * t

For conical helix change radius
radius = 12 * t

For variable pitch helix change the pitch
pitch = ( height/no_turns ) * t

* Interchange cos & sin for LH and RH helix

The values are just a sample to give you a feel.Change accordingly to your need

Hariharan B

 

[hudson888]

Simon,
Please let us know if I have misunderstood your question.

As of NX-3 helix curves are somewhat parametric. You can edit them and change the radius or pitch. You can set up an expression to make the change conditional if you wish. In effect you can change the length of the spring if you want to simply create an assembly that shows a spring adjusting to the position of whatever exists at either end.

I had taken the meaning of your question that you wanted to have a coil that varies both in diameter and pitch along its length in a fixed situation. One example would be that the coil is tightly wound at either end and has a greater pitch in the middle. It could also need to be smaller in diameter at the ends and fatter in the middle.

Hariharan B,

I think your example addresses the top paragraph above, (with a law controlled radius I think). I don't it allows for the pitch to get tighter or and looser differently from one end of the helix to the other. Please correct me if I'm wrong, and let us know what version of UG you're working with.

It appears that you have listed formulas to be used in expressions. If possible it may help if you were to describe how you use those expressions in terms of where in the dialogs they are to be called upon.

Best Regards

Hudson

 

[vbmec2007]

Hud,
The coil can change both in diameter and pitch along its length not in a fixed situation (electric heater element with rectangular profile along an helix curve).
I have the following input data:

1. start_radius
2. alfa_angle (to define the end_radius)
3. height_total (or turns)
4. height_z1
5. height_z2
6. ........
7. start_pitch (in z=0)
8. z1_pitch (in z=height_z1)
9. z2_pitch (in z=height_z2)
10 ........
11 end_pitch (in z=height_total)

Regards,

Simon

 

[hudson888]

Actually Hariharan B is on to something, once you figure out how to set up the law curve. Not an everyday thing for me, so I'm learning as I go. I think you should persevere with it though.

In the example you can vary the pitch or the radius, but the formula only allows that either should double in size per turn for the pitch and over the entire length for the radius.

You can make the helix elliptical also by changing the law.

Now. by changing the Z-axis definition I can easily vary the pitch in quite a few neat ways. But to do a good job of varying the radius I think I's have to create additional law curves to drive it by.

Getting closer

Regards

Hudson