This post is for Jonathan but anyone else that mist out in their early years in making one of these.
The post in the toy swap thread with the lovely purple heart wind up "tractor" toy reminded me of how much fun these were when i was a kid.
Perhaps you can introduce your grandchildren or other kids to them again and keep them alive.
Here is how they are made this guy most certainly did not invent them.
But better still here is you tube video of two climbing and racing.
Enjoy i think i might make one again just for fun.