Awwww, I just made a little tutorial to show how to do this and Xander-O beat me to the explanation!

Mirek: The graph editor is a really simple visualisation of your animation. Setting the infinity curve to cycle with offset is the easiest way answer the first part of diggersworld's query. Using the graph editor to deal with the second query, it's possible to control the speed manually but it's not possible to control the value of a key through SDK's.

Top explanation Xander

Take it easy,

Mat.