You could have an FSM on the main cube and set its rotation in the Y with a variable.
Then on the second cube do a Get FSM Float, to get the rotation from the first Cube then divide it by 2 except this time put the variable in the X (the one you created from the get FSM Float)..
This way the first cube could rotate at a speed of 20 and the second cube could rotate at a speed of 20 divided by 2 = 10.
Also I believe you are posting in the wrong forum section.