# Making very close Objects not to repel each other as Rigid Bodies ?

Hi , i have some rigid body objects , they are very close to each other.

when the simulation is played , the objects “jump” , as if they repel each other.

How do fix this behavior, and continue to have them collision with each other normally ?
thanx !

You can set the bounds of the objects to convex hull if they do not have their standard shape. Note: This does not work for hollow objects, like a bucket.

It should give very accurate collisions, hope it helps, else give a .blend

i tried that but it doesnt work

to copy all the phisics atributes press ctr+c in the list

thnax !

You have set all collision detection radii to 0.01, set the radius to 1.5 or something so that it covers the whole object shape for accurate collision detection.

And I don’t know if collisions between triangle mesh objects are calculated well, best use convex hull with compound bounds and use parent for more complex shapes. Triangle mesh is much harder for your computer.

Greetings! I’m not a pro at this, but I have a little experience with what you are trying to do…

The Bullet physics engine can be a bit fickle with object boundaries no matter what you use as a bounding method (Rigid, Convex Hull).

I use two methods to circumvent this:

1. scale your meshes in the scene larger (mesh-wise, leave the object scale at 1.0)

I’ll example this with a bowling game analogy:
A bowling lane is 60 feet (20 meters) a bowling pin is 15 inches ( 0.426 meters) I believe that conventionally, you should use metric measures for Blender, but if I did, the pins behaved irratically, and would float above the lane. :^(
so I used emperical measures and scaled my lane and pins (60 and 1.25 units, respectfully). Collisions behave well, however because my objects are so “large” (a bowling pin 1.25 meters tall) they seemed to fall in a slightly slower motion.

1. my recommended suggestion is to produce collision meshes. Smaller, simpler versions of the meshes you “see” in your scene. Set you visible meshes to “no collision”, parent your simpler collision meshes to them, and set those as invisible.

for my bowling example, I produced very simple ‘skinnier, smaller’ bowling pins and parented them to my visible pins. I then modified the smaller collision pins until the visible pins appeared to sit comfortably on the lane and reacted well.

Hope this helps. Joyous Blending!

man , thanx !

but i gotta read it a coule of times ,

can you post a blend file in mediafie ? if you can, of course

No prob!

It’s small, I’ll post a blend, right…here:

collsample.blend (220 KB)

I wasn’t kidding about the bowling pins, it’s the best example I have. :o

2 collision pins and to ‘visible’ pins as samples. Press P to see how they behave.

edit: try lifting and/or rotating the collision pins (the show pins are parented and will follow) then pressing P to watch their behavior. You’ll see that the larger set of pins falls slowly. strange huh?

coool !

now i understand a bit more what you meant , ill try it with my scene , hope it works !

thanx !

Physics objects have margin. Basically meaning they are considered slightly larger by physics than they are in actuality. To reduce the difference between the graphical object and the physics object, just edit the margin value in the advanced menu. This is a little easier than scaling all of your objects, which essentially achieves the same effect.

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man ,

that actually worked !

yuhuuuuuuuuuuuuuuuuuu!

thanx a bunch !