Rubber bands

[Roland Melkert]

I'm working on a generic rubber band template for LDCad 1.3 but noticed there are no rubber band parts in the official library, so I'm a bit unclear on the dimensions and shape to use for it.

I noticed most technic poly wheels have different bevels, yet the only part name reference I could find state the band is 'square'.

Any pointers from would be appreciated.

I'm using this for now:

ldcRubberBandSeg.dat

Code:

1 16 0 0 0 2 0 0 0 1 0 0 0 2 box4o8a.dat
1 16 0 0 0 2 0 0 0 1 0 0 0 2 ldcConRect-4-4.dat
1 16 0 1 0 2 0 0 0 1 0 0 0 2 ldcConRect-4-4.dat

ldcConRect-4-4.dat

Code:

5 24    -1  0  -1    1 0 -1    -1  1  -1   -1  -1  -1
5 24     1  0  -1    1 0  1     1  1  -1    1  -1  -1
5 24     1  0   1   -1 0  1     1  1   1    1  -1   1
5 24    -1  0   1   -1 0 -1    -1  1   1   -1  -1   1

It produces something like the attached little model.

[Philippe Hurbain]

There are two kinds of belt used in Technic models, black rubber ones with a square section, and colored ones, with round section and made from much more durable (silicon?) elastomer. Imho the way you modeled the square version is not very realistic, because most pulleys have a toroidal or V-shaped groove, and the square rubber band turns 45°. See this page I wrote in my very early LDraw days (11 years ago!!!).

[Roland Melkert]

That's a very informative page, thanks.

So if I rotate my first attempt by 45deg, and create a second one using e.g. a six sided tube most situations would be covered?

[Steffen]

could you please upload the rubber band creation donor parts as primitives to the parts tracker?

[Philippe Hurbain]

I think so... though to be completely realistic, square rubber belts can also lay flat (eg. when taught around a pin, or a beam). For an example of a model that uses lots of belts in unconventional situations, see BIs of 8002 set (SW Destroyer Droid)

[Roland Melkert]

Thanks,

Those band shapes as used in the sw model shouldn't be a problem, because my generating code supports unlimited circles (poly's) to shape the band's path. You can even mix in a few normal bezier curves to force some very weird segments.

Only thing that isn't possible at the moment is to 'roll' the band it self so it would be flat on e.g a bush while 45 deg rotated on the wheel. But I'm thinking to add a parameter for that too.

[Roland Melkert]

I think you mean Philio's dat files?

Because mine are used in generating closed mesh shapes using my LDCad deform generator.

The resulting LDraw models using them won't have any need for the original donors while viewing in other software.

[Steffen]

hmm, I just meant to use those which can be used by Lsynth...

I'm thinking of just a little primitive which can get sweeped by that tool along some line
and which defines the diameter and shape of the rubber band.
Your tool could use that primitive for generating the non-sweeped data,
and LSYNTH could be used to sweep it.

I think that's pretty much what a primitive in our library is for.

[Michael Heidemann]

Yes, that is a very good point.

[Roland Melkert]

I see, maybe someone could create a basic (no closed mesh though) rubber band ring (for use in instructions) using a generic primitive subpart. Other tools could then use the same segment subpart to generate dynamic bands.

Based on this thread I'm using the following files for generating bands at the moment.

Feel free to reformat them to something useful in the official library. You probable want to leave out the ldcConRing*' stuff though.


Square (it's optional rotated by 45 deg, by the generator it self)

Code:

0 Donor segment for square rubber band
0 Name: ldcRubberBandSqSeg.dat
0 Author: LDCad
0 BFC CERTIFY CCW
0 !CATEGORY LDCad donor

0 Unofficial part

0 //Main 3d box segment
1 16 0 0 0 2 0 0 0 1 0 0 0 2 box4o8a.dat

0 //Conditional lines in between segments
0 //  The LDCad path deform generator will automatically remove outer (con)lines to prevent duplicate lines between segments.
0 //  It will also take care of segment overlapping control points
1 16 0 0 0 2 0 0 0 1 0 0 0 2 ldcConRect-4-4.dat
1 16 0 1 0 2 0 0 0 1 0 0 0 2 ldcConRect-4-4.dat

Code:

0 Conditional line rectangle (4-4)
0 Name: ldcConRect-4-4.dat
0 Author: LDCad
0 BFC CERTIFY CCW
0 !CATEGORY LDCad donor

0 Unofficial primitive

0 //Rectangle of conditional lines for use in-between segments.
0 //  When using this file realize scaling/rotating will move the control points and thus affects visibility of the edge.
0 //  The LDCad path deform generator will truncate them back to something useful when they overlap into another segment though.
5 24    -1  0  -1    1 0 -1    -1  1  -1   -1  -1  -1
5 24     1  0  -1    1 0  1     1  1  -1    1  -1  -1
5 24     1  0   1   -1 0  1     1  1   1    1  -1   1
5 24    -1  0   1   -1 0 -1    -1  1   1   -1  -1   1

Round band (couldn't find a res 8 cylinder primitive, so I generated one myself):

Code:

0 Donor segment for round rubber band
0 Name: ldcRubberBandRndSeg.dat
0 Author: LDCad
0 BFC CERTIFY CCW
0 !CATEGORY LDCad donor

0 Unofficial part

0 //Main 3d tube segment
1 16 0 0 0   2 0 0  0 1 0  0 0 2 ldcCyli8.dat

0 //Conditional lines in between segments
0 //  The LDCad path deform generator will automatically remove outer (con)lines to prevent duplicate lines between segments.
0 //  It will also take care of segment overlapping control points
1 16 0 0 0   2 0 0  0 1 0  0 0 2 ldcConRing8.dat
1 16 0 1 0   2 0 0  0 1 0  0 0 2 ldcConRing8.dat

Code:

0 LDC Donor primitive for cylinder of resolution 8
0 Name: ldcCyli8.dat
0 Author: LDCad
0 BFC CERTIFY CW
0 !CATEGORY LDCad donor

0 Unofficial primitive
4 16     0.000000 0.000000  1.000000     0.000000 1.000000  1.000000     0.707107 1.000000  0.707107     0.707107 0.000000  0.707107
4 16     0.707107 0.000000  0.707107     0.707107 1.000000  0.707107     1.000000 1.000000  0.000000     1.000000 0.000000  0.000000
4 16     1.000000 0.000000  0.000000     1.000000 1.000000  0.000000     0.707107 1.000000 -0.707107     0.707107 0.000000 -0.707107
4 16     0.707107 0.000000 -0.707107     0.707107 1.000000 -0.707107     0.000000 1.000000 -1.000000     0.000000 0.000000 -1.000000
4 16     0.000000 0.000000 -1.000000     0.000000 1.000000 -1.000000    -0.707107 1.000000 -0.707107    -0.707107 0.000000 -0.707107
4 16    -0.707107 0.000000 -0.707107    -0.707107 1.000000 -0.707107    -1.000000 1.000000 -0.000000    -1.000000 0.000000 -0.000000
4 16    -1.000000 0.000000 -0.000000    -1.000000 1.000000 -0.000000    -0.707107 1.000000  0.707107    -0.707107 0.000000  0.707107
4 16    -0.707107 0.000000  0.707107    -0.707107 1.000000  0.707107     0.000000 1.000000  1.000000     0.000000 0.000000  1.000000

5 24     0.000000 0.000000  1.000000     0.000000 1.000000  1.000000    -0.707107 0.000000  0.707107     0.707107 0.000000  0.707107
5 24     0.707107 0.000000  0.707107     0.707107 1.000000  0.707107     0.000000 0.000000  1.000000     1.000000 0.000000  0.000000
5 24     1.000000 0.000000  0.000000     1.000000 1.000000  0.000000     0.707107 0.000000  0.707107     0.707107 0.000000 -0.707107
5 24     0.707107 0.000000 -0.707107     0.707107 1.000000 -0.707107     1.000000 0.000000  0.000000     0.000000 0.000000 -1.000000
5 24     0.000000 0.000000 -1.000000     0.000000 1.000000 -1.000000     0.707107 0.000000 -0.707107    -0.707107 0.000000 -0.707107
5 24    -0.707107 0.000000 -0.707107    -0.707107 1.000000 -0.707107     0.000000 0.000000 -1.000000    -1.000000 0.000000 -0.000000
5 24    -1.000000 0.000000 -0.000000    -1.000000 1.000000 -0.000000    -0.707107 0.000000 -0.707107    -0.707107 0.000000  0.707107
5 24    -0.707107 0.000000  0.707107    -0.707107 1.000000  0.707107    -1.000000 0.000000 -0.000000     0.000000 0.000000  1.000000

Code:

0 Conditional line ring for resolution 8 cylinder
0 Name: ldcConRing8.dat
0 Author: LDCad
0 BFC CERTIFY CW
0 !CATEGORY LDCad donor

0 Unofficial primitive

0 //Ring of conditional lines for use in-between segments.
0 //  When using this file realize scaling/rotating will move the control points and thus affects visibility of the edge.
0 //  The LDCad path deform generator will truncate them back to something useful when they overlap into another segment though.

5 24     0.000000 0.000000  1.000000     0.707107 0.000000  0.707107     0.000000 -1.000000  1.000000     0.000000 1.000000  1.000000
5 24     0.707107 0.000000  0.707107     1.000000 0.000000  0.000000     0.707107 -1.000000  0.707107     0.707107 1.000000  0.707107
5 24     1.000000 0.000000  0.000000     0.707107 0.000000 -0.707107     1.000000 -1.000000  0.000000     1.000000 1.000000  0.000000
5 24     0.707107 0.000000 -0.707107     0.000000 0.000000 -1.000000     0.707107 -1.000000 -0.707107     0.707107 1.000000 -0.707107
5 24     0.000000 0.000000 -1.000000    -0.707107 0.000000 -0.707107     0.000000 -1.000000 -1.000000     0.000000 1.000000 -1.000000
5 24    -0.707107 0.000000 -0.707107    -1.000000 0.000000 -0.000000    -0.707107 -1.000000 -0.707107    -0.707107 1.000000 -0.707107
5 24    -1.000000 0.000000 -0.000000    -0.707107 0.000000  0.707107    -1.000000 -1.000000 -0.000000    -1.000000 1.000000 -0.000000
5 24    -0.707107 0.000000  0.707107     0.000000 0.000000  1.000000    -0.707107 -1.000000  0.707107    -0.707107 1.000000  0.707107

These aren't the definitive ones so there might be less then perfect

[Philippe Hurbain]

Just for the record, I created a few round belts recently (85543, 85545 & 85546) for use in BOMs

[Roland Melkert]

Nice,

I only suggested a complete band cause I seem to remember only used primitives/subparts are allowed in the official library. Not completely sure about that though.

Anyway I'm guessing those bands don't use segment subparts?

[Roland Melkert]

Only thing that isn't possible at the moment is to 'roll' the band it self so it would be flat on e.g a bush while 45 deg rotated on the wheel.

I've managed to include this too in the current version, making pretty much any kind of band possible.

Attached is a model demonstrating the latest donor files/generator.

It should be more realistic then the model in opening post.