thank you for your detailed suggestion.
There is one problem - Bongo doesn’t allow to animate the _ExtendCurve. So, the trick would be to find a geometry driven rotational manipulation. Extent arc by point could be a way, but the history doesn’t work for this.
(…thinking … thinking … testing…)
I got it - two arc segments with a wide gap. HistoryOn and Arcblend create a new arc segment. This can be use as flow target. Now if I rotate one of the first arc segments than the arcblendcurve will be extended and stays a circle segment. The pocket fan is wided along a changing arc.
Now I can perfect solve my animation problem. Last I rendered the wallet of the link it was luck to synchronize the movement of the wallet and the morphing fan. The fan morphing was not good, distortions was there. But now I can make the second arcblend-segment as child of the rotating cover, the fan will perfect follow the cover. I’m so happy, it’s makes the animation easy and stable.
Thank you very much for taking time to push ideas. You are a great help.