Board Thread:Naruto Discussions/@comment-26367861-20161025235033/@comment-3965545-20161026220906

Madara chakra and Sasuke chakra may not have the same signature, or anything but they carry the essense of Indra hence their chakras being able to mix with Hashi, Naruto chakra which carries the essence of Ashura's chakra. Ashura and Indra each possess half of the essense of Hagoromo's chakra. SO TTJ Madara had that in him... Obito would have awakened the Rinnegan if he didn't die.. but it would have taken some time. So you need a bit of Hashi/Naruto chakra plus the Sharingan(Kabuto only said Sharingan and Madara didn't argue so you were right on not needing Mangekyo, UltimaDude) eventually awakens Rinnegan for an Uchiha. Madara/Sasuke chakra plus stolen Sharingan eyes equals Rinnegan for a Senju/Uzumaki.. Or if Hashi/Naruto took Madara/Sasuke's eyes they would get Rinnegan.

edit

It seems you need to be able to generate the chakra, so you need the flesh/body part of the transmigrant along with the chakra... for an Uchiha you also need a pair of eyes that belong together. Therefor it would have been impossible for Obito to attain the Rinnegan because he did not have Madara's Rinnegan = flesh/body part.. and when he did have it he did not have his eye pair.