In this instructible, I will give the instructions as clearly as i can however, i am making this instructible after having completed all of the cannons, so the pictures will Not include the cannons under construction. However, i feel that the designs are pretty self explanatory when you get a good look at the finished product.
Always be careful when firing these cannons! They work though internal combustion processes of flamable gasses caused by electric shock discharge. Be afraid. But above all, just be responsible. Dont shoot at people, animals, or priceless vases.
Step 1: History of Cannons
I started out experimenting with different ignition sources like tazers, camera flash shocks, and grill ignitors to ignite various fuels inside my various size cannons. The biggest of which had a 2" diameter barrel and was 5' tall. It shot completely over a nearby cornfield.
Then it occurred to me that I was continually trying to build one bigger and bigger and better. So I decided to try and design one out of the smallest parts. So Spitball Cannon version 1 (SC1) came along. It was so much fun blasting the little thing at friends (dont do it though) I continued to try to improve it for efficiency, hand comfort, effectiveness, cool looks, and safety.
I also tried to accomplish the same task (shooting a spitball) by other means. SC2 was made to shoot from pressurized air. Originally I intended to fit it into a large magic marker to conceal it, but it ended up being too big, too ineffective, and it didnt make a cool blast!
SC3 was made to fit the hand better, store ammo in it, use a tube to inject fuel into it, and look better, but the combustion chamber was too small to work reliably. So i combined concepts from SC1 and SC3 to create SC4. At this point i thought that this design could not be improved very much more, (at least not cheaply or easily). SO it sat for a year......
One day i happened to pick it up and play with it for a while on the same day i chose to spray paint some furniture. After having the gun fresh in my mind, i picked up a spray can spraying tool handle and PING, the lightbulb lit up in my head. Thus the creation of SC5, the "big shot".
Moral of the story is that there is always another way of doing the same thing. It just took time, setting down the project and coming back later. Research is also important to help guide you on your way; why not learn from other's mistakes and build off their success (just remember to Aways give credit where its due).