Found the Micro Servo Robot on letsmakerobots.com. I thought this little thing was awesome but wanted a 3D printable version that would pick up marbles instead. Plus, I only had 10k potentiometers which seem like they would work better with 3D printed parts anyway. Here is the link to the project I derived this from: http://letsmakerobots.com/robot/project/micro-servo-robot.
Update: Added Arduino program with English Comments.
You will need:
4 - SG90 Micro Servos
4 - 10k potentiometers
1 - Arduino Uno with Breadboard shield
Misc wire and some marbles!
Minimum plastic is used. I generated supports for the Marble Shute with MeshMixer but included the original file as well if you wanted to create your own.
Dual marbleShute alternating task...