You can do away with the sphere and just move the origin point to where you want it to pivot from. If you click on the "A" to bring up the object attributes dialog you should see something that says show origin, or something like that. Check it and exit out of the object attributes dialog and you should see a green dot. You can place that wherever you want the pivot point to be. I have found that if you have grouped objects you need to ungroup them, set your origins and linking, then regroup leaving out the children. By children I mean the linked objects. The objects they are linked to are the parents. If you do not ungroup before you assign linking, then you get strange rotations when you go to animate.