Equations in animator

[OliverManhire]

I have heard that animator only performs a partial rebuild in between frames and that equations will not update. If this is true then my problem is this: I want to animate gears running in sync with each other and since the gears are different sizes, I can't just use an angle mate or other simple mate relation. I'm not sure if physical dynamics will do this or even if I want to use it or not. Does anyone know an easy way to animate these gears?

Regards

Oliver