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Double Helix

16 REPLIES 16
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Message 1 of 17
DuncanAnderson
3599 Views, 16 Replies

Double Helix


I need some ideas about creating a double helix. Consider the filament in an incandescent light bulb with a strand is coiled and the coil is coiled.

 

I can think of two potential solutions.
First is to create a complex 3D path and sweep – how would I create that path so I can keep control. By which I mean, I would need to be able to enter the inner, minor coil diameter and the outer, major diameter.
Second would be to create the helix using a coil function, but selecting an axis that is normal to the profile sketch plane and then using the Part Bend function with a Bend Line at an angle.

I’ve tried the latter, but Inv swore and me and then stopped talking to me 😞


Any sensible suggestions welcome

 

 

Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
16 REPLIES 16
Message 2 of 17
JDMather
in reply to: DuncanAnderson

What version of Inventor are you using?

I posted an Equation Curve (produced by one of my students) a few months ago.

 

Also, I have started experimenting with the Bridge Curve function to tie in ends of curves like this to straight lines.


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Message 3 of 17
DuncanAnderson
in reply to: JDMather

Currently using 2012, hoping to move to 2014 very soon

 

Do you have a link for this equation curve

 

Two quick searches either produced too many hits or nothing of any relevance.

 

 

Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 4 of 17
pcrawley
in reply to: DuncanAnderson

Using 3ds max to model it is surprisingly easy if you are just looking for a non-parametric model in Inventor.  

Attached as an IGES and an Inventor 2103 file (because I don't have 2012 here).

 

In max you just create one helix, normalize it, then path-deform it around another normalized helix.  Export the IGES and bring it into Inventor.

 

It's actually highlighted a slight problem with Inventor 2014.  Importing the IGES on my machine lets me see the model for a split second before crashing Smiley Frustrated  2013 works a treat.

Peter
Message 5 of 17
glenn-chun
in reply to: DuncanAnderson


duncan wrote:

Do you have a link for this equation curve?


Hi Duncan,

 

I just posted this.  Hope it helps.

 

Equation for Helix along Helix
http://forums.autodesk.com/t5/Autodesk-Inventor/Equation-for-Helix-along-Helix/td-p/4352925

 

Glenn

ASM Development



Glenn Chun
Sr. Principal Engineer
Message 6 of 17
DuncanAnderson
in reply to: glenn-chun

.
Thanks Glenn

Currently using Inv2012sp2. However I can use Excel equations and import the Points and connect with a 3D Spline
Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 7 of 17
DuncanAnderson
in reply to: glenn-chun

.
Glenn, I think i might have found a flaw, the orientation of the second helix in relation to the orientation of the first helix 😕 😞
Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 8 of 17
glenn-chun
in reply to: DuncanAnderson

Hi Duncan,

 

I also noticed a subtle problem with the orientation of the second helix.  It's a little slanted in relation to the orientation of the first helix.

 

Could you try the following equation instead?  This may not be what you want, but sweep works better along this path.

 

x(t): (R + r * sin(turns * t * 1rad)) * cos(t * 1rad)
y(t): (R + r * sin(turns * t * 1rad)) * sin(t * 1rad)
z(t): Z * t + r * cos(turns * t * 1rad)
t_min: 0
t_max: Turns * 2*PI

 

where

R is the radius of the first helix,

r is the radius of the second helix,

Turns is the number of turns for the first helix,

turns is the number of turns for the second helix (in one turn of the first helix),

Pitch is the pitch of the first helix, and

Z is Pitch / (2*PI)

 

Glenn



Glenn Chun
Sr. Principal Engineer
Message 9 of 17
DuncanAnderson
in reply to: JDMather

.

I create my own equations that have the over generalised form of,

x(t)=cos{f[t]}+cos({g[t]}+incr)

y(t)=sin{f[t]}+sin({g[t]}+incr)

z(t)=0<t<[distance]

 

I'll give a better answer to Glenn

 

 

Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 10 of 17
DuncanAnderson
in reply to: glenn-chun

.

 

This is the generalised equation I used

 

x(t)=(RAD.COS(DIR.2.pi.Z/PITCH))  +(rad.COS((dir.2.pi.Dist/pitch)+(Pass.2.pi/Nos)))

 

y(t)=(RAD.SIN(DIR.2.pi.Z/PITCH))  +(rad.SIN((dir.2.pi.Dist/pitch)+(Pass.2.pi/Nos)))

 

z(t)=Dist.[0<t<1]

 

Where

Dist = length of double helix

 

RAD = Radius of Major Helix

DIR = Direction of rotation {+=ccw, -=cw}

PITCH = Pitch of Major Helix

 

rad = radius of minor helix

pitch = pitch of minor helix

 

Pass = increment number

Nos = number of increments

 

It isn't possible to use the standard circular pattern/polar array command as the the pattern needs to be revolved around a helix. Therefore, the minor helix needs to be incremented around the major helix mathamatically.

Wire Rope

Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 11 of 17

Hi Duncan,

 

I don't suppose you'd be willing to share the ipt you based that image upon?

I've tried using your equation but I must be missing something in Inventor 2013 as the formula doesn't work for me.

 

Thanks,

 

Alex.

Message 12 of 17

.

 

Sorry, can't share the IPT.

 

Can you can have the spreadsheets they were based upon.

 

I was using Inv2012sp2, which meant importing points, conected by a 3D spline, from a spreadsheet.

 

Four combinations of direction; CW/CW, CW/CCW, CCW/CCW, CCW/CW.

 

I've had to edit the titles of each input to protect comercial confidentiallity. I might have made a few spelling mistakes, but you should be able to figure.

 

HTHs

 

 

Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 13 of 17

Thanks for the files. 🙂

I can't look in detail at the spreadsheets as I'm viewingbthem on my phone but I assume you have formulae driving the values from the cells in yellow?
Message 14 of 17

.
Correct

When you open the spreadsheets and look at the formulas behind the cells you'll be able to understand the equations I posted.
Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}
Message 15 of 17

Can I get a file for that, or maybe the equation? I'm young enough that I haven't learned those areas of math.

Message 16 of 17
glenn-chun
in reply to: noahpsullivan

Up until Inventor 2014, we've used equation curves to model twisted pair cables.  Now in Inventor 2015, we can use the new Twist option in the Sweep feature to model them.

 

From online help for Inventor 2015 > What's New > Part:

 

sweep_twist.png

 

Glenn



Glenn Chun
Sr. Principal Engineer
Message 17 of 17

.

 

Dogs5336,

 

If you go back to the message posted 08-14-2013 11:38 AM you'll find the generalised equations.

 

If you go back to the message posted 10-29-2013 02:29 PM you'll find those equations in four MS Excel spreadsheets.

 

HTHs

 

Duncan Anderson

"Humour is one man shouting gibberish in the face of authority, and proving by fabricated insanity that nothing could be as mad as what passes for ordinary living." {Terence 'Spike' Milligan KBE (16 Apr 1918 – 27 Feb 2002)}

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