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| Bumlinger... |
 Posted: Tue Oct 27, 2009 10:16 pm |
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Guest
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I need to create a helical curve that is normal to an existing helical
curve. A spiral on a spiral so to speak. I have found several curve
equations that are close, but what usually happens is that the
secondary curve is not swept normal to the primary curve. The primary
curve is created by cylindrical equation like this:
r = 0.75
theta = 360 * t * 4.5
z = 0 - 19.05 * t
It is the equation that sweeps the secondary curve that eludes me.
Surely, someone must have done this before. Any ideas? |
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| Bumlinger... |
| Posted: Wed Oct 28, 2009 12:28 pm |
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Guest
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On Oct 28, 4:55 am, David Geesaman <dgeesamanNOS... at (no spam) yahooooo.com>
wrote:
Quote: Bumlinger wrote:
I need to create a helical curve that is normal to an existing helical
curve. A spiral on a spiral so to speak. I have found several curve
equations that are close, but what usually happens is that the
secondary curve is not swept normal to the primary curve. The primary
curve is created by cylindrical equation like this:
r = 0.75
theta = 360 * t * 4.5
z = 0 - 19.05 * t
It is the equation that sweeps the secondary curve that eludes me.
Surely, someone must have done this before. Any ideas?
I don't really follow your description yet.
Does this shape look like a coil formed into a helical curve? Like if
you formed a phone cord into a spring?
David
Yes, exactly that. A phone cord formed into a spring is an accurate
description. |
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| David Geesaman... |
| Posted: Wed Oct 28, 2009 1:55 pm |
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Guest
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Bumlinger wrote:
Quote: I need to create a helical curve that is normal to an existing helical
curve. A spiral on a spiral so to speak. I have found several curve
equations that are close, but what usually happens is that the
secondary curve is not swept normal to the primary curve. The primary
curve is created by cylindrical equation like this:
r = 0.75
theta = 360 * t * 4.5
z = 0 - 19.05 * t
It is the equation that sweeps the secondary curve that eludes me.
Surely, someone must have done this before. Any ideas?
I don't really follow your description yet.
Does this shape look like a coil formed into a helical curve? Like if
you formed a phone cord into a spring?
David |
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| Janes... |
| Posted: Thu Oct 29, 2009 5:15 am |
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Guest
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"David Geesaman" <dgeesamanNOSPAM at (no spam) yahooooo.com> wrote in message news:hc94fc02nb at (no spam) news5.newsguy.com...
Bumlinger wrote:
Quote: I need to create a helical curve that is normal to an existing helical
curve. A spiral on a spiral so to speak. I have found several curve
equations that are close, but what usually happens is that the
secondary curve is not swept normal to the primary curve. The primary
curve is created by cylindrical equation like this:
r = 0.75
theta = 360 * t * 4.5
z = 0 - 19.05 * t
It is the equation that sweeps the secondary curve that eludes me.
Surely, someone must have done this before. Any ideas?
I don't really follow your description yet.
Does this shape look like a coil formed into a helical curve? Like if
you formed a phone cord into a spring?
David
THIS IS A CLASSIC FROM '04, MAYBE WUTCHER LOOKIN FOR
Expert Advice Ask the Product Manager Tips and Tricks »
Technical Tutorials
Home » Customer Resources » Tools & Tutorials » Expert Advice » Tips and Tricks
Tips and Tricks
Creating a Helical Spring Around a Non-Linear Trajectory
This technique will go through the steps for creating a helical shaped solid using a variable section sweep, a sketcher relation that makes use of the trajpar parameter and a swept protrusion. This technique does not use the actual #Helical Sweep feature.
Figure 1
1. Sketch a curve that defines the trajectory (shape) of the spring. Then create another curve parallel to the original by selecting #Feature, #Copy, selecting on the original curve and using the #Translate option to create a copy that is parallel to the original curve.
Figure 2
2. Create a surface using a variable section sweep: Select #Feature, #Create, #Advanced, #Done, #Var Sec Sweep, #Done. Select the default options for the feature, select one curve for the Origin Trajectory and the other curve for the X-Vector trajectory. Then sketch the section below. Note: Actual dimensions may vary.
Before completing the section, write the following sketcher relation: sd# = trajpar*360*N, where sd# is the symbol of the angular dimension in the sketch and N is the number of coils.
Figure 3
3. Next create a swept protrusion using the outside edge of the surface as your trajectory: Select #Feature, #Create, #Protrusion, #Sweep, #Solid and #Done. Use the default options for the feature and when selecting the trajectory, use #Tangent Chain and select the outside edge of the surface. Now sketch your desired section on the cross-hairs (centerlines) as seen below.
Figure 4
4. Finally, the surface and datum curves may be placed on a layer and blanked to show the resulting helical coil. |
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| Peter... |
| Posted: Fri Oct 30, 2009 6:49 pm |
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On Oct 27, 5:16 pm, Bumlinger <samuel.halg... at (no spam) gmail.com> wrote:
Quote: I need to create a helical curve that is normal to an existing helical
curve. A spiral on a spiral so to speak. I have found several curve
equations that are close, but what usually happens is that the
secondary curve is not swept normal to the primary curve. The primary
curve is created by cylindrical equation like this:
r = 0.75
theta = 360 * t * 4.5
z = 0 - 19.05 * t
It is the equation that sweeps the secondary curve that eludes me.
Surely, someone must have done this before. Any ideas?
I have dug out an equation that I believe is what you may be looking
for.
It produces what looks like a helical phone cord wound around a
helix.
Using a cylindrical CSYS, the equation is:
primary_turns = 8
primary_rad = 8
secondary_turns = 2
secondary_height = 60
theta = t * 360 * secondary_turns
r = 40 + primary_rad * cos (theta * primary_turns)
z = primary_rad * sin (theta * primary_turns) + (t *
secondary_height)
There are definitely much more elegant ways to write this equation but
as my old brain is slowing down, I find that I need all the help (and
prompts) that I can get.
An elliptical variable sweep (about 3.5 X 1.75) gives a better visual
result than a circle when trying to follow this curve.
Hope that it is what you wanted and that I am not too late posting
it.
Peter |
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| Bumlinger... |
| Posted: Mon Nov 02, 2009 3:16 pm |
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Guest
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On Oct 30, 12:49 pm, Peter <bea... at (no spam) execulink.com> wrote:
Quote: On Oct 27, 5:16 pm, Bumlinger <samuel.halg... at (no spam) gmail.com> wrote:
I need to create a helical curve that is normal to an existing helical
curve. A spiral on a spiral so to speak. I have found several curve
equations that are close, but what usually happens is that the
secondary curve is not swept normal to the primary curve. The primary
curve is created by cylindrical equation like this:
r = 0.75
theta = 360 * t * 4.5
z = 0 - 19.05 * t
It is the equation that sweeps the secondary curve that eludes me.
Surely, someone must have done this before. Any ideas?
I have dug out an equation that I believe is what you may be looking
for.
It produces what looks like a helical phone cord wound around a
helix.
Using a cylindrical CSYS, the equation is:
primary_turns = 8
primary_rad = 8
secondary_turns = 2
secondary_height = 60
theta = t * 360 * secondary_turns
r = 40 + primary_rad * cos (theta * primary_turns)
z = primary_rad * sin (theta * primary_turns) + (t *
secondary_height)
There are definitely much more elegant ways to write this equation but
as my old brain is slowing down, I find that I need all the help (and
prompts) that I can get.
An elliptical variable sweep (about 3.5 X 1.75) gives a better visual
result than a circle when trying to follow this curve.
Hope that it is what you wanted and that I am not too late posting
it.
Peter
Peter,
Thanks for the formula, it is close but not quite right. I need the
orientation of the spiral to be normal to the helical sweep
trajectory. The spiral your formula produces is oriented such that
the spiral is parallel to the "sketch" plane (if there was one) as it
rotates about the main axis through the coordinate system. Think of a
plane through the axis that rotates with the sweep as the curve moves
down the z direction. I have a graphic, but do not know know how to
show it in this forum. |
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