We proto-typed a double shooter and thought we could make it work.
In our release video at 0:28
http://www.youtube.com/watch?feature...MCYh1Prs#t=28s
You can see this being shot.
We found you have to delay the second shot, the disks could not fly ontop of each other 100 millisecond delay will work.
We moved on to build this double deck design as seen here in the build season pictures. You can see several pictures.
http://www.flickr.com/photos/teamthr...57632841870583
But later, we could not separate the frisbee stacks into two channels in this manner. So after fighting it for a week or so...we gave up, closed the second hole. But what we found was that the second wheel gave us the momentum to shoot rapid fire. The total weight of the shooter wheels are 2.2 lbs. This allowed for some rapid fire with no loss in speed.
Later we improved this to shoot around 1.3 seconds all 4 disks with a single shooter. As see below. 2-3 disk are in the air before the first one hits the goal.
http://www.youtube.com/watch?feature...&v=yI_XldiEXFM
That's kind of our design story. We learned lot from this.