lol! hey, vk, want to write the sequel to my book??? ;) now with the tread-thing, somebody got a cylinder to work in that instance, by parenting magnets to the gears. as the cylinder rotates through the magnet zones, the magnets pull it into the proper shape. also, as the there gear things move, they pass their magnets and zones through the cylinder to keep it in the right shape. of course, this wouldn't work with your train track example. :)