It prints using a regular marker of any color.
Maybe it doesn't have a great resolution but this is a project that I really wanted to do.
Step 1: Materials
Try to find one with a bipolar motor for the laser, mine used a regular dc motor and I changed it later for a stepper motor.
Also you will need another stepper motor with a rubber wheel and a wooden base.
Electronic stuff is detailed in other step.
Step 2: First motor
The pick up laser and the other motor are not used.
Step 3: Second motor
Cut the plastic with a dremell and then use a sand paper to remove the excess.
Step 4: Finish the cartridge
Use a piece of plastic, attach the dc motor to one of the sides and then glue all this over the guides of pick up laser.
Step 5: Marker holder
Is a plastic tube with a hole on one side. Over that hole I glued a plastic nut with a screw.
This piece must be glued to the last reduction gear.