Cush dR4IVE BEARING

I replaced my cush drive bearing last night and my bike feels a whole lot smoother. The question is, why when the cush drive bearing is rooted did I only feel roughness on take off? I assume from what I can see that the bearing is constantly spinning and spinning at the same speed as the wheel bearing?

.. if the bearing is rooted (your description) then you get free play and/or roughness in the bearing itself.

on a mudderboike, the cush drive (and its bearing ) really only comes into play when you accelerate
so
what you describing - 'roughness on take off' is correct

Thanks, but still confused as to why it isn't rough when cruising - it is still spinning from what I can tell?

When you accelerate the sprocket carrier can deflect causing chain misalignment (rough!). So the roughness that you feel is not really the rough bearing but the chain misalignment which the rooted bearing has allowed.
At least that's what I found with my bike. Also, if you ride it like that for ages you will find that your sprockets wear out really really fast.

Thanks, but still confused as to why it isn't rough when cruising - it is still spinning from what I can tell?

When cruising, everything is spinning together as a unit. On takeoff, ALL the load is on the cush drive.