I've been thinking about this device for years, but i haven't had the base or the huge amount of track it would take. It might be fun to take to a show; a use for the old code 100 track after you switch to fine scale. What I would start with is a 4 foot square sheet of Homasote or such. In the center mark 4 points in a 1" sqaure. One should be in the center of the sheet. Pick the point farthest off center and draw a quarter circle at 24" radius in the opposite quadtrant of the board, let's say upper right. Now shift to the point to the right; reduce the radius by 1"; and draw another arc. Keep shifting the center around and reducing the radius. The centers wikk rotate in the opposite direction to the arcs. When you get to the first quadrant again, you'll be in 4". 4 times around and you'll be doing streetcar radii. You may want to put a large radius or straight track before the beginning. Now just lay and wire the track. You have built a spiral (not a helix!). Put a loco on the starting track and slowly wind it into the center to see where it binds, derails or shorts out. Run it in again backwards. A second spiral in the opposite direction would also be handy. Can you get a buddy to do it? I think 4 feet square would do for HO, be very generous for N, and be totally inadequate for O. Did I explain it clearly enough?