Dynamics Problem - floaters!!

[lightningad]

I have modelled a tray into which i have a thousand small coloured bricks being dropped in.

The bricks are being directed into the tray using an invisible funnel - because my cloner object is using an image object to control the colours of the clones and is too wide to drop in cleanly.

I have a Collider body tag on both the tray and the funnel, and i have a rigid dynamics tag on the cloner object.

When i run the simulation the bricks fall in, but then they float above the tray base and they stay roughly a centimetre from the tray walls. It also appears that the floating plane is not perfectly flat but tilting to one side and some of the bricks are breaking through the tray base slightly.

please can you suggest areas that might be the issue?
i cannot see any settings that would suggest a "force field" around the boundaries. I have also set the Scene Scale (in Project settings/Simulation to 6.5mm because that is the size of each brick, and i was told to match those to help stop the bricks vibrating constantly.

i tried to add a project file but i cannot make it smaller than 3.2mb and the upload says theres a limit of 2mb files.

thanks
Adam

[lightningad]

i have got a bit further...
i found a different set of Project Settings called Bullet - and i here found a Collision Margin setting set to 1cm. I dropped it to 2mm and the floating seems to be resolved, but now the bricks are definitely breaking through the model . I also set the Scene Scale back to 1000mm and its made no difference.

How do stop the breaking through from happening?

[Dr. Sassi]

Hi lightningad,

I will leave this upload link for a short moment here.
-Upload link removed- I got the data.

I will have a look into your settings.

All the best

[lightningad]

@Dr-Sassi - thanks...just uploaded the files. You might recognise the project as the same one you have already given me invaluable help with!!

[Dr. Sassi]

Thanks a lot, lightningad.

It is way past midnight here, and I will have a look in the morning.

Cheers

[lightningad]

i think i might have solved the problems (almost !)
By changing the shape and size of the funnel - i am no longer loosing bricks outside the drop zone.
The Project Settings/Bullet need these settings - Collision Margin - 0.5mm, Scale 6.5mm, Steps per frame -30, Solver Iterations - 30
Now the bricks are behaving almost exactly as i want - the wireframe show a few breaking through the base of the tray, but as they are not seen i'm less concerned.

[Dr. Sassi]

Hi lightningad,

Please have a look here:
https://stcineversityprod02.blob.core.windows.net/$web/Cineversity_Forum_Support/2023_PROJECTS_DRS/20230428_CV4_2023_drs_23_DYbr_01.c4d.zip

I used a little trick here, as the scale of your project is set up very small.
However, the laws of physics do not care. Since we typically have aero dynamics off, we work in a vacuum, which provides the Gravity experiment condition that we might all have learned back in the day. A feather falls equally like a steel ball.
The same is true for large and small objects.
Gravity is 9.81 meters per second squared, based on the distance to the center of the earth, a little bit less on high mountains

Anyway, if you accelerate an object in a vacuum by 9.81 meters per second squared, that affects an object a kilometer, a mile, or just a cm, perhaps a few millimeters, in size in the same way.
But if you look at it from a considerable distance or under a magnifying glass, the speed is in the body size of the object in a different ratio. The smaller the scale, the heavier the effect would be a simple observation.

This means Gravity is given much more movement in the scene relative to its size, as all objects move at the same speed based on that. Since I will clarify that if we see a train on the horizon, moving a meter in a second, we might not notice any change.
If we look at an apple on a table while sitting on that table, if the apple rolls one meter per second, that will look relatively fast.

Gravity puts energy into the system. Hence, I tend to lower the Gravity if the scale is very small. To toss your tiny elements into a box is not a three-second event. It is below a second, which would be no pleasure to observe. Hence why we filmmakers stretch time; if something important happens, often the chosen effect slows down a tiny bit. It is the equivalent of attention.

So, as a side effect of that super fast motion that Gravity would provide, again relative to the scene's size, we need to ramp up the Steps, as you did.

The Elements are also more Cube-like, so to leave the shape on automatically will cause trouble, time-wise and calculation-wise.

There is more but minor; it is all in the scene, and some tweaks will improve it even more.

My best wishes for your project.

[lightningad]

@Dr-Sassi thank you for the explanation...makes a lot of sense when you explain it like that.

I do have one question...
i reset the dynamics on my model to match yours and i noticed that the very start of the animation when the bricks start to fall, they seem to explode outwards in all directions, and when the gravity is lower this explosion appears larger (obviously lower gravity lets the particles move further before they are caught and pulled down).

What causes this explosion to happen? in the absence of any other applied force i would expect things to simply fall downwards not outwards.

regards
Adam

[Dr. Sassi]

Hi Adam,

Thanks a lot for the feedback.

The explosion happens based on the shape form. To produce any kind of reasonable solving time, the project is set to Dynamic Tag> Collision> Shape [Box]
This assumes a box that covers the Object itself, and the calculation is done on a box, not the many segments of the Object.

These boxes intersect in your project. Creating the worse case of a collision So it explodes.

If that is not wanted, the Moving Mesh shape would be taken, and with a setup, as we have here, that would take a lot of time.
One option would be to leave Box as a shape and decrease its size. (Here: -0.2cm)

Or try the Dynamic Tag> Collision> Shape [Another Object]; Object, and use one or the other Object from the file below

CV4_2023_drs_23_DYbr_11.c4d

No collision might happen when it is too small, and you might move a collider into it.

All the best

[lightningad]

@Dr-Sassi
THANK YOU!!

I tried the different settings as suggested and found that using Box as the size caused other problems ( the bricks piled too high in the box to close it!). I had been using Automatic before and it was still piling too high, but not as high as with Box.

So tried a couple of other Shapes and found Ellipsoid works perfectly (with shape size set to 0mm)...a good drop of bricks with much less explosion, and it also lays much more level making the animation work as intended.

best regards
Adam

[Dr. Sassi]

Nice that you found a sweet spot spot for your project, Adam.

My best wishes for your project.