Hi guys, this is not a help topic for me, it is for everyone.
I search for months how to solve this problem and i never find answers anywhere.
So, i give here the simple solution, because polycount is well referenced on google.
So, How to export from C4D to UDK with this f*cking smoothing groups ?
Simple : export in .fbx, and at import, check "import explicit normals".
In fact, the error message about missing smoothing group continue to appear in udk.
This is why we are so many to test everything, check/uncheck things at export/import, and we did not see that we had found the solution sometimes.
Enjoy your c4d export.