You have to adjust the ellipsoid to match your model dimensions, for example try (2,6,2) instead of (2,2,2). In addition, i'm not sure if the gravity part of your code is actually working correctly for such a large model. Keep in mind that jPCT offers no magic "everything works as expected"-collision method for all cases. You might have to try a few things and understand how it works to use the provided methods in a way that the actual outcome matches your requirements.