Dave,
Not sure about plans on all of thse, but doing some more digging should tunr up more details.
A big one I remember in RMC, now on Youtube:
http://www.youtube.com/watch?v=XLbqnw2bKeI
Less complex, HO and N loaders:
http://www.youtube.com/watch?v=9eG07HYvEEs
http://www.youtube.com/watch?v=6uxnLq5oiWw
Earlier discussion here:
http://cs.trains.com/mrr/f/11/t/172846.aspx
More:
http://model-railroad-hobbyist.com/magazine/mrh-2012-12-dec/modeling-coal-loader-p1
http://forum.atlasrr.com/forum/topic.asp?ARCHIVE=true&TOPIC_ID=32193