Twisted Rubber Band Motor

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  11 November 2013
Twisted Rubber Band Motor

Hi -

I hope I'm going to have better luck asking this question here at CG Society than other places.

I'm trying to make a twisted rubber band motor that winds up and unwinds. And is attached on one side to a stationary object and on the other side the object spins/twists with the rotation of the rubber band both winding up and un-winding.

I tried using some simple objects to attempt this in C4D - two tubes with colider tags, and a third to act as the rubber band with a cloth tag and nurbs after deleting all but the exterior ring of polys. But, it jitters out once the two sides of the rubber band touch andbreaks through polys (each side of the rubber band through the other).

I tried using the cloth - cloth nurbs. I tried uping the steps and iterations,calculations, subdividing the Cloth nurbs to a rediculous amount (which helped, i got 720 degree turn before breaking through polys, but it killed my comp)

I tried using a twist deformer - which twisted it more like a DNA strand. Not what I'm after.

So... I'm kinda lost - as I need not just one rubber band - but several in the end. 14 to 16 total. All winding up and un-winding.

I did just find a video which shows exactly what I want to achieve but it was made in Abaqus.

Here it is:



As mentioned - I'm kinda lost as to what area in C4D to achieve this effect.

Xpresso maybe?

ps - there are other objects that have to attach to this rubber band motor.

Can any one point me in the right direction in C4D to create this?

PSS - I hope there's not a problem using the little Youtube icon to post and show the example vid - or any of the other little icons is there...? I don't want to get ousted first question for using the wrong ones.
 
  11 November 2013
Anyone?
or is this something that C4D can't do?

Create a rubber band that winds up and un-winds without breaking through polys that is.

tia
 
  11 November 2013
Have you tried using a helix and a spline wrap and mesh deformer?
Animate the angles of the helix, set the radii to very small so it's a straight line as you begin.
Create a flat model of the rubber band with both sides next to each other (as in the initial stage).
Also create a box, subdivided for deformation which will then act as a mesh for the Mesh deformer. First set up the Mesh deformer with the model of your rubber band. Then apply the spline wrap to the box. Using restriction tag and vertex weights you can restrict which portion of the box will be deformed (you want to keep the ends the undeformed).
Mileage may vary, some tweaking might be required.
 
  11 November 2013
Before you set off down a road of pain... do you just need to get the visual animation of it winding up and down, or do you genuinely need a real physics engine to actually calculate the twist and stretching of the rubber surface?

I ask, because more and more Im seeing people trying to invoke physics engines to do the animation where a blindingly simple bend or twist deformer would work.
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  11 November 2013
I've made a quick setup using xpresso as the spline wrap seems to fail when it comes to high twist settings. This is the principle - you will need to adjust it to fit your needs.
Setup is simple - the cubes connect via tracer to form a spline for the rubber band (sweep - and an instance of the tracer somewhat offset to create the rail ), they rotate around the centre. Their rotation depends on where in the hierarchy they are. They also scale down as they rotate to simulate the tightening. The cubes are also spread out using the position of the end null.
Attached Files
File Type: zip rubber band.zip (70.8 KB, 18 views)
 
  11 November 2013
Originally Posted by imashination: Before you set off down a road of pain... do you just need to get the visual animation of it winding up and down, or do you genuinely need a real physics engine to actually calculate the twist and stretching of the rubber surface?

I ask, because more and more Im seeing people trying to invoke physics engines to do the animation where a blindingly simple bend or twist deformer would work.


I've been thinking perhaps what I'm asking C4D to do is more appropriate for a CAD type program or one that can do the physic syms. I do understand the difference between the two.

And in answer to your question: in a nut shell yes I'm looking to end up with between 1k and 1.8k twists of the rubber band. Thinking if you use a deformer - and have it go back to original state it would then "act" like the real thing and it's motion on the motor side would drive the next object. Or I could just add a motor to simulate it driving it.

I tried a twist deformer on a pair of splines as well a torus - but stopped since it was simulating more a DNA strand effect.

In both cases it broke through with hardly any full rotations on the twist deformer.

Again I may be asking too much of C4D. or rather asking it to do something it wasn't meant to do in the first place. Where a CAD software would be more suited. but then you lack the visual.

Perhaps 3DS Max may handle it - or Houdini? I haven't worked extensively with them - but I do know both have a physics side to them that is supposed to be pretty stout. When looking at airfoil sym - 3DS Max has either a plugin or module that does just that.

I'm still looking at C4D to see what is possible.

Quote: Have you tried using a helix and a spline wrap and mesh deformer?
Animate the angles of the helix, set the radii to very small so it's a straight line as you begin.
Create a flat model of the rubber band with both sides next to each other (as in the initial stage).
Also create a box, subdivided for deformation which will then act as a mesh for the Mesh deformer. First set up the Mesh deformer with the model of your rubber band. Then apply the spline wrap to the box. Using restriction tag and vertex weights you can restrict which portion of the box will be deformed (you want to keep the ends the undeformed).
Mileage may vary, some tweaking might be required.


will give this a try - thanx!

Quote: I've made a quick setup using xpresso as the spline wrap seems to fail when it comes to high twist settings. This is the principle - you will need to adjust it to fit your needs.
Setup is simple - the cubes connect via tracer to form a spline for the rubber band (sweep - and an instance of the tracer somewhat offset to create the rail ), they rotate around the centre. Their rotation depends on where in the hierarchy they are. They also scale down as they rotate to simulate the tightening. The cubes are also spread out using the position of the end null.


Thanx for going the extra mile Zmurowski. I'll take a look at what you did and what you stated above.

Is this example in R13? if above - I won't be able to open it...
I've been jonesing for the newer Releases since hearing about R14 and the addition of a "Flight" tag I think its called.

Should be soon fingers crossed, but a new desktop is a must first. I'm looking into building one asap. Especially after this week-end. A simple blocked out 24 second animation, 36 hours into a probable 46 hour render time and C4D gliched and froze up. Not blaming C4D - it's the comp i'm sure. But lost all couldn't save it due to a hard restart of the comp was nessasary.

oh well - i'm kinda use to that - but it's a sign for sure it's time for new comp. I'll use this one as a render node or something. Maybe a audio workstation.

At any rate - thankyou both much for the replies.

I will try to open your attached file - before you reply most likely. And give a try at your suggestion.

If I can't do a actuall physics sim in C4D I suppose I could go at it in another way. Perhaps morphing a twisted one to an un twisted one... at the boundary of actually twisting one.

Just cut it short of where it breaks through. Then morph it to a fully twisted one - add rotation to the fully twisted one to simulate it spinning. Something along those lines.

any more thoughts on this are welcome as well. Attacking this from all angles with more than one mind - hopefully will prove successful.
 
  11 November 2013
I did find someone else that tried a twisted rubber band in C4D (r12) - Stephano Tartarotti



It's a nicely made model of a rubber band driven aeroplane no doubt. And the guy has obviously a ton of experience in C4D with over 600 models he's selling at 3DExport that he's made.

Thought I would post it to show that style of making a twisted rubber band look can be done for others that might happen upon this thread.

From what I can see in his wireframe render of the same model:



it looks as though he used the helix and made it as you would to simulate a wound wire. Which are easy enough to make. If that's the look one is after.

Last edited by chasecanade : 11 November 2013 at 08:48 PM.
 
  11 November 2013
From what I can see on the Stefano model ... the supports would cave in on each other
without a solid shaft keeping the distance between them, in which case, two single strands
of rubber band would work as they twisted and wrapped over the shaft of the rod supports
... imho
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David

iMac 3.06 ghz Intel Core 2 Duo / 16 GB / OS 10.9.5 / C4D StudioR12 / CS6

R.I.P. 11.02.11 ... my dear friend .
 
  11 November 2013
Hang on, you're pointing out the the design faults in a rubber band driven passenger aircraft?
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  11 November 2013
LMAO ...

Having actually built a number of these as a kid, I couldn't help it
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David

iMac 3.06 ghz Intel Core 2 Duo / 16 GB / OS 10.9.5 / C4D StudioR12 / CS6

R.I.P. 11.02.11 ... my dear friend .

Last edited by vid2k2 : 11 November 2013 at 01:27 PM.
 
  11 November 2013
Wrong post...

Cheers,
Brian
 
  11 November 2013
Originally Posted by vid2k2: LMAO ...

Having actually built a number of these as a kid, I couldn't help it


I have to admit, I would love to see someone build one to human scale. It would be a short flight, but a fun one!

W
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@WillMacNeil_VFX
 
  11 November 2013
Sorry about the delay - work, classes and a downed access prevented me from responding sooner.

First off - I did accomplish it using cloth. First with a single rubber band then with three twisting around each other.

The single - eh - I wasn't impressed with. It looks too much like a oil dipstick twisted. But my comp didn't bog down like before.

The triple looks closer to real life imo.
The downside was in using 3 rubber bands my poly count was over a mill. lol but it worked.



@ imashination - from what you were saying and what I took away from it, you were right, I was over thinking things and perhaps over complicating it. I was focused more on the physics of the rubber band than trying to mimic the physics. And how it would look.

I did try using just a couple cubes and a twist deformer. It looks passable and I think it will work with some more tweaking and animating properties.

@ Zmurowski - Thank you again for going the extra mile. I took a look at what you made. It has the properties of the stretch but from frame 48 and expecially on frame 70 you can see where the helix starts to do some weird things to the spline and they cross through each other. On frame 70 looking at front view ( i think) you can see were it is flat and more like a DNA strand flattened out. This is what I was getting as well when using splines, hence I shied away from using them for this.

I do have to ask though - were did you pick up on your Xpresso knowledge? I can figure out quite a bit of it - but not how you arrived at what was needed from the get go. My Xpresso knowledge is lacking to say the least.

If you wouldn't mind - would you go through it either here or in a new thread? I see how you built it. And understand 80% of that - but not the why so much and how you came up with knowing what was needed where.

As well can you point me to a couple solid sources to beef up my chops for using Xpresso?

Yeah I was impressed. It was like you did it so matter of factually. Guess that comes with knowing your shhhhaving cream brands.

Thanx to both of you - you really helped me out. Taking a little bit of what each of you stated - and showed me via example. I think I put something together that will visually be exceptable.

On a side note: I discovered by accident really what or how Stephano Tartarotti did his (I'm pretty sure) He used a single cube and gave a ton of rotations. The reason it's so squared off is due to the lack of subdivisions. If I remember correctly subdivisions need to be at 10% of the revolutions to maintain smoothness on the curves.


@ Kokosing - I believe they have made a model of that plane. Not life size As well I think they have an electric one very similar to it that I've seen recently. At HK maybe..? It's a styro bird. It does look pretty cool though. Stephano stated he made it from a cartoon drawing he saw...
 
  11 November 2013
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