This is a penny crossbow I designed in Fusion 360 that only needs a penny and a few rubber bands to work. The more rubber bands you use, the more walls you will need. I used three rubber bands and seven walls for the best distance while also not breaking the cross bow.

The assembly instructions are:

Slide the penny holder into the v slot on the crossbow,

place the rubber bands around one of the rods on the side

,

wrap a string around the rubber bands and pull the string and rubber bands through the hole on the penny shooter,

Finally wrap the other ends of the rubber bands around the other rod on the crossbow.

The penny shooter is now ready for a penny and you to pull it back and shoot it.