How do I make a hole in a rigid body object that works?

Hi, I am trying to do something as simple as getting a box to fall into a hole in another, bigger (physics) box.
The only thing that can do that is supposedly Triangle Mesh, but Triangle Mesh is extremely screwed up.
Triangle Mesh objects seem to fall halfway through the ground, bounce around and do other retarded crap.

Basically, I have a box with a hole in it. It is a rigid body.
I have another rigid body that is just a box smaller then the hole.

I want the box with the hole to be able to fall and fit around the box without jerking around, flying into space, falling through the ground, trying to kill tigers with cotton balls, getting lawyers to be honest or something stupid like that.

What is wrong with the Triangle Mesh boundary and are there any workarounds?

Hi,

There is nothing wrong with Triangle Mesh collision detection, but you’re using it in the wrong situation. It’s not intended for use only on static objects (e.g. terrains). I think you need to need to create a compound object from a number of Convex Hull boundary objects.

I have no problems with what you’re describing… see my attached file.

A few things to try:
Apply Scale/Rot data to the object. This will make sure that physics bounds are calculated correctly. To do this, select the object and press Ctrl-A.

Increase the mass of the main box so that it’s not the same as the other boxes. Bigger mass means that the other boxes won’t affect the big box as much (as you’d expect with smaller objects hitting larger objects).

If you’re still having problems, post your blend.

Attachments

trimesh.blend (36.2 KB)

Take a look at the attatched file.
I know I can simply use rotation/location locks for the door thing, but it has nothing to do with my point.
This file has a door with a circular hole on one of the sides.
In the circular hole is a smaller static cylinder.
It should rotate fine, but when the box hits it the door starts peeling off of the cylinder.

Also, especially if you turn the box into a rigid body, the box seems to clip straight through one face of the door and only collide with the other face.

Attachments

badbadbadbadbadbad.blend (143 KB)

Really? I’m not noticing what you’re describing. The box seems to rotate normally.

What version of Blender are you using?

I might add that this isn’t the best way to do “hinged” objects. There are things called “rigid body joints” that are available in the Object buttons (click “Add constraint” and choose “Rigid body joint.”)

I’d mess around with that instead of the method that you’re using.

-Sam

How can I use the constraints to achieve the same door effect?
When I try, they don’t work properly at all.

The settings are pretty simple.

You have 3 types of joints: Ball, Hinge, and Generic 6DOF. I have no idea what the last one is… so play with it if you want, but the other two are what you need.

Both types will rotate along the pivot point specified (select the “showpivot” button to see where this is). Ball joints will rotate along whatever axis it feels like (all over the place), and Hinge joints will rotate along only one axis (the X axis actually).

You can offset the pivot point with the PivotX, Y, and Z values. With showpivot enabled you can easily place this in the right spot. For the Hinge joint, the axis of the pivot point is also important, and you can change this with Ax X, Y, and Z.

See my example file for a basic hinged rigid body.

-Sam

Attachments

rigidbodyjoint.blend (60.3 KB)