I guess gravity is a secret?
We're working on our design that uses a rather tall collecting/storage system, which delivers balls to a slanted hopper. The intake of the shooter is at the bottom of the hopper. The hopper can hold 3 balls. We decided we need the hopper to hold the balls so they can be fed to the shooter on demand, rather than as they pop out of the collector. We plan to use a pneumatic cylinder to push the next ball in line up into the shooter.