Periscope Drive

I'm going to use a Hitec Servo for the power winch. I've made a small rotation drum that will pull a Nylon string and move the plateform up and down.
I'm using Nylon string because everything else I looked at had to much resistance to curl around the drum.
I also put a small drum pulley at the top of the setup for the string to ride on while pulling the plateform.
Although gravity would be enough to pull the plateform back down, I added a very light weight spring to the side of the slide. This gives very little resistance, But it's just enough to pull the plateform back down. It also seems to have added some stability to the plateform.