How to animate an aperture?


#1

The idea is to illustrate a sodium channel through the membrane of a nerve cell. It is basically a molecular pore that opens to admit a sodium ion.

The question is, what is the best way to make an aperture? I have sketched and animated in Bongo a traditional camera type aperture, in which multiple blades rotate to open the camera shutter. But there should be a much simpler way.

What I have in mind is a simple Rhino surface, a disk with a tiny hole in the middle. In Bongo, at point 50 on the timeline, I would like to scale up the tiny central hole to the diameter of the full opening of the aperture.

The problem I have encountered is that the scale command does not seem to operate on holes. It seems to scale up a circle instead.

If I ignore Bongo, I find I can pretty easily scale up a hole in a surface using Solidptson and Scale2D. But this doesn’t work in Bongo.

Thank you for your insights on how to do this.

Michael


#2

Hey Michael, i have found that you have to use a command which is called BongoScale. how to use it in a 1d or in your case 2d manner is also described see here i have no idea if you can scale a hole with this but maybe somebody chimes in who knows how to work with bongo or you ask in that link i placed.

But if you excuse me some ranting, you animate something which has a scale of about 10.000 times/ms and you want to display it as a surface with a hole in it?.. …its somehow neither esthetically nor scientifically :smiley: well never mind.

may i ask what its for?


(Luc Adriaenssen) #3

The trick is to use History Recording.
Install 2 circles and let one of them BongoScale to 0 (zero) at tick 50 (or something), hence creating 2 keyframes. Then with ‘Record Histroy’ enabled (Rhino’s statusbar at the bottom) apply Rhino’s Loft command on the circles.It doesn’t matter what tick the timelineslider is at at the time.

Unfortunately History Recordings aren’t redrawn when the animation is ‘Played’ (Previewed). You can get a (bit shaky) Preview though by pressing and holding down left mouse button (not clicking) the small right/left arrow buttons of the timeline slider.

Afterwards you can move the keyframes around (also create newones) the to get the desired operation.
When you want to relocate the animated surface, move both the circles but not the lofted surface thus ‘breaking’ the History (the surface will move along with the circles).

Instead of Loft also Rhino’s PlanarSrf command could be used, but this command cannot cope with coinciding curves.

aperture.3dm (92.4 KB)

Luc

PS Obviously the use of circles isn’t imperative. This technique works with whatever curves or polylines.


#4

Luc, thank you very much. This is the solution. I downloaded your file and experimented with some of my own. Bongo resists scaling directly to zero, but if I enter values near zero, like .0001, it pops to zero. Otherwise it all works and it is especially helpful that the technique is not confined to circles. In life, the actual aperture is thought to be cruciform.

Richard, thank you for your link. The idea is to animate the mechanism of a single pore, not the porosity of a membrane.

Thanks again. Michael


(Luc Adriaenssen) #5

Forgot to mention. Sorry.

To be correct: it doesn’t pop to zero, it only looks like that. Actually the value remains 0.0001 - as you can see when you increase the Edit-box-precision in the Bongo’s Options dialog:

Precision doesn’t go beyond 0.000001 (1e-6) though - the uppermost negative scaling Rhino itself allows. Also scaling up is best limited to 1e6 (1,000,000) to obtain acceptable accuracy. It all has to do with exactitudes in calculations with floating point numbers (the IEEE 754 doubles - https://en.wikipedia.org/wiki/Double-precision_floating-point_format) used by the software. But that’s beyond my field of competence. :relaxed:


#6

[Luc] Luc https://discourse.mcneel.com/users/luc McNeel
November 21

mcg:

Bongo resists scaling directly to zero

Forgot to mention. Sorry.

To be correct: it doesn’t pop to zero, it only looks like that.
Actually the value remains 0.0001 - as you can see when you increase
the Edit-box-precision in the Bongo’s Options dialog:

Precision doesn’t go beyond 0.000001 (1e-6) though - the uppermost
negative scaling Rhino itself allows. Also scaling up is best limited
to 1e6 (1,000,000) to obtain acceptable accuracy. It all has to do
with exactitudes in calculations with floating point numbers (the IEEE
754 doubles -
https://en.wikipedia.org/wiki/Double-precision_floating-point_format)
used by the software. But that’s beyond my field of competence. :relaxed:


Visit Topic
https://discourse.mcneel.com/t/how-to-animate-an-aperture/38874/5 or
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    In Reply To

[mcg] mcg https://discourse.mcneel.com/users/mcg
November 18

Luc, thank you very much. This is the solution. I downloaded your file
and experimented with some of my own. Bongo resists scaling directly
to zero, but if I enter values near zero, like .0001, it pops to zero.
Otherwise it all works and it is especially helpful that the technique
is not confined …


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Thanks for amplifying on this, Luc. I will stick with 10^-4. This
initial “closed” aperture seems to be invisible.

Michael

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