Remember? You'll need the magnet.
- Glue some adhesive tape (Scotch, Tesa, whatever) on both sides of the Neodym magnet disc, to protect it from scattering.
- Insert the disc into the slot of the cannon.
- If you don't want it to be able to fall out (Kids?) then close the slot with some glue. Be cautious: The magnet must be able to move somewhat in the slot (horizontally) to give the momentum to the nest ball. I used a handheld 3d printer pen to apply some PLA into the slot (The while PLA in the picture)