Returning CD-ROM Wheel

This science project wil show you how to make a returning CD-ROM wheel.
This experiment is usually done with a tin can, but here you can see what is happening inside.
http://www.metacafe.com/watch/791395/returning_cd_rom_wheel

Get 2 used CD-ROM's. These will be the 2 sides of the wheel.

Draw the following template with a CD-ROM. The 4 rounded holes will be needed to assemble the wheel. The 2 holes marked with a square are the elastic band holes for the interior mechanism.

Cut the template and stack it on top of the 2 CD-ROMs

Use a dremel to drill the 6 holes

You will get the following:
In yellow: 2 holes for the elastic bands
In red: 4 holes for the mounting screws

Get a dowel and masking tape.
Cut 4 pieces of dowel, each one the width of a masking tape as shown.

Get a heavy bolt and a piece of string. Attach the bolt with the string. This will be the internal mechanism that will make the CD-ROM wheel return.

Assemble the dowels to the 2 CD-ROMs with 4 screws.
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.

Attach the bolt at the intersection of the elastic bands.
Gently roll the CD-ROM wheel away from you.
It will roll forward, stop and return back!
You can see the results on the following video: