How to correctly create bullet rigid from custom .mesh in Ogre?

Question

Being new to 3d programming and bullet physics in particular, I am wondering how a 3d model or the mesh generated out of it effects the accuracy of bullet physics simulation.

I have written a small Ogre 3d application in C++, including/using bullet for physics. In a small scene I add a plane as ground and three boxes (simple blender objects that come with Ogre) that have their initial position a bit over that ground. So after starting the application those three boxes fall down until they hit the ground plane, where they move a bit, depending on their initial height and rotation, until they come to a halt.

Watching that scene the bullet physics simulation looks very accurate and realistic, also the boxes seem to touch the ground very exactly.

Ok, then I have created a box model in Sketchup 8 and exported it to an Ogre .mesh file. Then I use this model instead for those three boxes in my scene. The C++ code itself is not changed at all (except that I load the new .mesh file for the boxes).

However, even though on the screen those new box models look exactly as the original ones, their movement is not correct any more. They fall to the ground plane fine, but then they move very weird, it looks not as realistic as before. Even worse, after they have stopped their movement those three boxes now "float" a bit over the ground plane, they do not touch it. I can also see their shadow now below the box on the plane, so they are really not touching the ground plane.

TL;DR: Scene with three boxes, falling down to the ground, simulated by bullet. That works fine with default Ogre (blender) .mesh files for the boxes. But with custom Sketchup models (.mesh files) instead for the boxes, but the same code, the bullet simulation does not work correctly any more.

My question is: how does the mesh of a model impact the accuracy of bullet?
And: what can I do to solve that issue with my custom Sketchup models?

PS: I load the .mesh file and convert it to a bullet rigid body as following:

m_pSceneMgr->createEntity("Cube1", "Cube.mesh");
...
BtOgre::StaticMeshToShapeConverter converter(m_pSceneMgr->getEntity("Cube1"));
btCollisionShape* colShape = converter.createBox();

Answer 1

Found the solution to my problem. I simply needed to set model's origin in Sketchup to its bounding box's center, now bullet works correctly in my scene again :)

Answer 2

I am not a Ogre user, but I really think your problem is related to the createBox() call.

Since you loaded your later cube from a mesh file, it is a regular convex mesh, not necessarily interpretable as a box by BtOgre. Calling createConvex() instead would probably fix it.

This is because the loaded cube would be now treated as a mesh, which happens to be a box.