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Dynamics Collision Margin problem

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Ben Janowitz
Dynamics Collision Margin problem
on Mar 28, 2018 at 10:29:22 am

Hi guys, I'm struggling getting dynamics right on my projects, in general. The issue I'm having is, I guess, with the collision margin.
In other worlds:

I don't like in the project settings the collision margin set to 1 cm, I like to have it near the 0. If I have a Floor element as a collider body, this is not a problem. I usually up the steps per frame to have a nice flow on the dynamics and that's it. The problem comes when I use another object as a collider body, a thin cube for example or anything else. In these case, dynamics stop working as soon as the objects collide. No matter what I insert on step per frame (I've tried also 100-ish numbers) I can't get it working right, so I'm pretty sure it's something I'm missing.

Here you go the c4d file and a screenshot of the scene:

12297_dynamicsproblem.c4d.zip



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Jim Scott
Re: Dynamics Collision Margin problem
on Mar 28, 2018 at 3:02:27 pm

Hi Ben,

Just what do you want to happen (or are expecting to happen) with the dynamic objects in your scene? If you want the cylinder and arm to roll away under the power of the motor I found that the default dynamics settings did just that. Otherwise, please elaborate on what you want to accomplish.





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Ben Janowitz
Re: Dynamics Collision Margin problem
on Mar 28, 2018 at 4:10:21 pm

Thanks for the answer. Sure.
What I want is to have the collision margin set to 0 cause I don’t want a 1 cm gap on the renders. But as soon as I set the collision margin to something below 0 my dynamics stop to working. Thi scene it’s just an example, but this thing happens to me all the time, soft body, rigid bodh etc. As far as I use floor as a collider body all it’s good even with low value on the collision margin option, but if I change shape, for example plane or cube everything stops


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Jim Scott
Re: Dynamics Collision Margin problem
on Mar 28, 2018 at 5:51:17 pm
Last Edited By Jim Scott on Mar 28, 2018 at 6:24:11 pm

I have never noticed this issue before in typical dynamic's scenarios of bouncing balls or falling blocks, but I can see what you mean that the gap is noticeable from certain angles and close distances for your example project. Scale settings can cause issues in projects when using objects considerably larger or smaller than the default 100 cm, so try reducing the Scale value in the project's Dynamics settings. I tried a Collision Margin of .1 cm, and a Scale value of 10 cm, and unless your camera is zoomed in quite close, and fairly level with the floor, the gap isn't noticeable and the dynamics seem to run fine. If you really need a 0 cm gap I don't know how to achieve that with your example. Perhaps someone else will be more knowledgeable on this issue.

Edit: another possibility would be to use "Another Object" for the collision Shape of the plank on the floor by using a duplicate of that plank which is lowered a bit and hidden from the editor and renderer. That way the collision margin could be left at the default (or at least above 0), and the plank that is rendering will fill in the gap.

Edit #2: Now that I have tried my first edit and found that it doesn't work quite as I expected, what would work is to use another plank that is lower and hidden as the collision object, and just have the visible one fill in the gap. Or perhaps I should just stop putting my foot in my mouth and let someone else help with your problem. ;)


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Ben Janowitz
Re: Dynamics Collision Margin problem
on Apr 5, 2018 at 3:37:49 pm

Ahahaha, no thanks really. The scale value trick did enough for me...at least for what I have to achieve now. Messing up with invisible planes as etc...is something I wanna avoid right now.
Thanks!


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