Ok guys... I'll hurry... but now the bad part... I need your help: It's a bit tricky but I know you'll understand... I try to be clear: A is parented to Ulna D is parented to Humerus when I rotate E ulna rotates and A follows Ulna. to make the piston I've done: B parented to A A is tracking D origin handle of B is in the centre of A C parented to D D is tracking A origin handle of C is in the centre of D when I rotate E all the system works, and I'm really happy... when I save all the system as .obp and than I load it as bryce object A is not more tracking D and D is not more tracking A. WHY? why Bryce is not saving this setings?? it is a bit frustrating.... everytime I load the arm I have to track A to D and D to A, ok 20 sec operation, but annoying... any idea?