If you link the rotater to an active activation module, then it will rotater 45°. There are two ways of rotating endlessly. If you link the rotater to 9 active activation modules, it will set the rotation angle to endless. If you put a button directly next to the rotater and link it to the rotater, whenever the rotater finishes rotating, it will send a signal to the button which will tell it to rotate again. So since you want it to only spin while you have it activated, instead of a button, use an AND-gate. Link the rotater and an activation module to the AND-gate, and link the AND-gate to the rotater. It has to be directly next to the rotater or else it will just make whatever's rotating undock. The rotater should also be linked to a single active activation module so it spins 45° at a time. You can even use the same activation module that is linked to the AND-gate I think. So when the rotating thing finishes rotating, it will send a signal to the AND-gate, and it the activation module is also on, it will be told to rotate again.
Edit: Sorry for the wall of text XD