This experiment is usually done with a tin can, but here you can see what is happening inside.
Step 2: Drilling template
Step 5: Drilled CD-ROM
In yellow: 2 holes for the elastic bands
In red: 4 holes for the mounting screws
Step 6: Dowels
Cut 4 pieces of dowel, each one the width of a masking tape as shown.
Step 7: Internal Mechanism
Step 8: Assembly
Insert 2 elastic bands in the elastic holes and hold them with nails as shown. The elastics bands need to cross in the middle of the assembly.