In 3D software, such as 3D Studio Max,Maya,Blender,etc you can move the pivot point where ever you like, typically you center it to object but some times it may need to be some where else, like for example for a door, the pivot needs to be where the hinges are instead of center so it acts like a door with hinges and not a revolving door.
However, once you export the object/model as a .obj for importing into VP, it will ignore this pivot point and use the world axis center as the pivot point instead. The world axis is the center point of the 3D world environment which is highlighted in yellow in this pic below, the position in 3D software will be 0,0,0. In this pic the object is lined up so that its pivot point center is lined up with the world axis center, you can see where the objects pivot is by the XYZ arrow/move gizmo.
So as this is currently, we can rotate it on the X axis and it will rotate like a roller, but if we rotate it on the Y or Z axis it will rotate end over end.
If we have our object off center from the world axis center (the center of the grid) it will throw off the rotation of the object in VP. In this next pic I have moved the objects pivot point to be at the world axis center while the object is moved away from the world axis center to demonstrate this. An example of when you would intentionally want this, is Uncle Willy’s Dracula in Monster bash, since he moves on an arc his pivot needs to be set away from him.
So when we rotate this object on the Y axis it will go around the center world axis like so:
Note how each axis is color coordinated on the rotation gizmo. (Yes gizmo is the technical term!)
There are some instances where you have multiple 3D objects that fit together to form one toy, two good examples are both Frankenstein’s monster’s. Frank on M.S Frankenstein has rotating head, and arms that throw, while Monster Bash Frank rises up on a table then lifts his arms. In these cases you will have to set the pivot using world axis (0,0,0) for each object then assemble them in vp. What I suggest you do is export the model with all it’s pieces as one object, then import all the pieces separately, that way you have a model of reference that’s already perfectly assembled.