I am trying to put a random rss feed in the main (application) view.
The code works if I surf to /feed/, but if I use the same partial
outside of views/feeds/ I get errors about nil objects. It seems that
the partial does not automatically use it's controller.
Partials and views don't belong to a controller in particular (except in the sense that their location on disk implies the controller that normally uses them). Your partial probably depends on the controller having setup some instance variable which you are setting up in your FeedController, but not elsewhere.