parts moving out in mid air during animation

I have an animation that has a mechanism that once it all moves into place the whole mechanism rotates around an axis.





The problem that I have is that when is starts to rotate the mechanism parts fly out into space and come back to the final frame shot.



I have the assembly connection set to rigid but do I need to set it to something different.



I've got a feeling that it's something very simple but its still something simple that I don't know!!!



Cheers for any help