This is the machine that my son built over the two days following the visit to the steam tractor show:

Those pulleys, for those of you who don't live and breath Lego, are actually wheel bases.  (Now you know why I'm looking forward to those 14 additional wheel sets. )  Don't tell DS, but grandma is getting the Kinex set that integrates with the Legos and includes gear pieces.  He is going to be buiding some awesome things in January!