prolems with Bullet physic

I dont know if i am doing somethign wrong but here is my problem: If i turn on the “dynamic” button for an object to make it affected by gravity everything is ok if the object is a cube or a sphere but if the object is more complex-shaped it goes crazy and i just cant make it stand on the ground like it should. I dont know it there are some rules i need to follow when applying physics to complex meshes or something. Any help would be good

In your logic buttons, there is a button called bounds. Click it and select “Convex Hull Polytope”.