I got an idea on how to build a helix but I am not excatly for sure. I am wanting to go up 18" with a HO scale. Can I run the track on top of each other or do I start out with a bigger radius and get smaller. I want two tracks to go up. I want them to pull about 30 cars so I know it can't have to much of a incline. If anyone can I would really appreciate it.