Actually, I started this idea about three weeks ago.  We got the idea from ancient Chinese tops.  We saw a movie about it.  First we figured we needed to put a string on it it.  It didn't have any weight.  To be heavier inside  we filled it with bottle caps..  The hardest part was figuring out how to keep it going and how to get it spinning without it just falling over, that wouldn't be too cool.  That's when we got the idea to add the second string to hold it up.  It was very limited in the time it would spin, that's when we decided to add more string and therefore, make a longer lasting top.