Board Thread:Naruto Discussions/@comment-1512913-20170417105433/@comment-4912646-20170419031153

Obito actually did use the Rinnegan as well as Sharingan to control the tailed beasts, since it's apparently required to send chakra to the black stakes in their hearts and manifest the chakra chains to suppress them. The only time he explicitly uses the Sharingan on the beasts is when he suppresses Five-Tails after it turns on him, as we actually see the Sharingan appear in its eye. In fact, despite only having one Rinnegan, Obito claims his Outer Path binding power is much stronger than Nagato's (for some reason). Really wish that plot point had been elaborated on more though, the "body" half of the Sage's power making a better host for the Rinnegan than the "eye" half has never made any sense to me, especially since Obito had mastered control of Hashirama's cells.