In need of a creative solution!

[Acies]

another solution would be to create a model of the ring with the planet included, and do this for all three planets, so there is:

Ring + Planet 1
Ring + Planet 2
Ring + Planet 3
Ring + No_Planets

At first have the tablet spawned, and create three "Ring + No_Planets" on the tablet,
then when the player uses item 'Planet 1' on a ring, set the interacted ring inactive, and replace it with "Ring + Planet 1" - simples

Obviously create spin joints at the centre of each ring, so they rotate properly! I think this method would be quite easy to accomplish ( Only 5 models needed in total, 4 of them are almost identical ) and the rotation would be the most natural!

Good. This is actually the only possible way to do it. Since I have incorporated three wheels in one model I don't think the engine can distinguish between them. Using this I may actually salvage the model for some usage.

To Jennifer: I'm using Maya.

This model has caused much frustration for me. Almost angry I made it.