You will need to think about how you keep the cables tidy.
Here is a DIY solution based on winches. It takes a TV into a ceiling but could be adapted to raise/lower a projector. It uses a counterweight which is a good idea. I am not sure what locks the screen in the up position.
There are also commercial systems that might give you ideas, some of them seem pretty weird to me.
I like the idea of a telescoping hydraulic cylinder but I have not found one and it would probably be expensive.