You objects exist in object space, each in it's own. By applying transformations to them like rotations and translations, you transform them into world space. Usually, the game logic "thinks" in world space in most cases. Why i mentioned these spaces is simply because, depending on the model, your model's object space position might be off, so that you'll get confusing results. An example: If your object is located around 0,0,0 in object space, your camera hasn't moved and you are looking down the z-axis, a translation of your model by 0,0,100 will transform the object's center of (0,0,0) into the world space coordinates (0,0,100). And you would be able to see it as expected with your camera setup. However, if your model is centered around 0,0,-200 in object space, the translation will place it at (0,0,-100) in world space and your won't be able to see it without changing the camera. Or in other words: Make sure that your object's center is roughly where you expect it to be. I should be, but some exporters produces strange outputs. So there's always a chance that, if you don't see a model where you think that it should be, this might be the reason.