[MrBasse]

If it will only have 90 degrees of rotation, I would look at a potentiometer over an encoder. They are cheaper and can be used with any motor/gearbox combo pretty easily.

We have used single turn and ten turn pots pretty much every year to control simple systems.

How much force do you need? What kind of speed are you looking for? I like window motors for simple motion since they're cheap and easy to come by, but they are hard to interface with. You could also use a window wiper motor...