Since 3.0 it is importent to have the 0/0/0 at a specific point. Why? The Zero point is now also working as the mass center of the vehicle/plane. And if this center is not balanced the vehicle will start bouncing like hell.
What does that mean for modelling? Well, it means the model must build exact symmetric. The distance between the center of the front wheel box and the center of the back wheel box must have the same size, also the distance between the centers of the left and right wheel. On tanks, the track box must have the same size to the front as it has to the back of the model.
Building a new model with this knowledge is easy, you just have to build the model around the zero point.
But what is with model you want to update? These models have also to be moved that the zero point at the center between the wheels. Sound awful right? Moving every single part to a new place is a lot of work.
So how to do it in a simple way...
With Flans mod 3.0 i created a new parameter you can add to you model java file.
translateAll(0, 0, 0);
This parameter will move the models part for you, so you have only figure out the value (x/y/z) your model has to be moved.
translateAll(15, -2, 0);
This will move the complete model 15 px to the front and 2px up