Problems finding a way to change an object's centre of mass (Should be easy)?

Game Engine Game Engine Support and Discussion
#1

Hi, I want to find a way to change the centre of mass of a solid primitive (Cube, for instance), but I am having problems.

I figured it would be easy by editing the mesh of a cube and moving it, as the blue dot seems to be the centre of mass for physics objects.
However, with a simple test of balancing a long bar, the cube seems to have collision problems as seen in the attatched blend.

Attachment:
The test is simply two boxes, one a wall-like cube (Static, thing the cube balances on), and one the physics object (2x4-style long cube) with it’s mesh a little off to change the centre of mass.
When the centre of mass is placed on the balancing cube, it works fine. If you move the short side over the cube, it flips correctly.
However, as shown in the .blend, when the long side from the centre of mass is placed over the balancing cube, it goes straight through like a ghost.

I can’t explain it very well obviously so if you don’t understand what I’m saying just look at the blend.

How can I fix this OR how can I change the centre of mass/pivot of a single no-constraint physics object?
How can I fix the collision problem?

#2

You forgot the link. Make sure you select Bounds, otherwise, collisions are a sphere around the object center. But you’re right, the object center is its center of mass.

#3

whoops :o
It’s attached here.

I checked everything, applied scale, rotation and VT. It still doesn’t work properly. Perhaps it’s a bug?

Attachments

arr.blend (126 KB)

#4

I’ve looked at the blend and you need to make it a ‘Convex Hull’ in the Bounds section.