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Hi #MakerCamp , welcome to #WeirdScienceWednesday . We’ll be talking about combustion today, but even better, we’ll make combustion cannons for shooting ping pong balls, or whatever else you want to launch through the air.

My interest in cannons and combustion started back in high school, when an attempt to make a hydrogen converter went horribly wrong, shattering the florescent bulb in my garage and singeing my eyebrows off. After changing my pants, I looked at what was left and thought, “Hmmmmmm…”

The rest is history. I soon cobbled together a suitable cannon-ish device that could propel small 3/4-inch dowels through about five layers of cardboard, and that was fun, but I had to do more — it always had to be bigger, louder, more reliable, and more powerful. So I kept building. I would build some for me, some for friends, and they kept growing in size and complexity. (My personal favorite is this one: http://goo.gl/QLYO2

The cannon we’ll be building today, however, is not quite so complex. It's built with PVC pipe, and the combustion is provided by igniting aerosol gas with a spark from a piezoelectric BBQ igniter. Simply spray the aerosol into the combustion chamber, put the cap on to seal it off, and press the igniter button. The gas ignites, causing an intense amount of pressure that launches the ping pong projectile. 

My photo instructions are down below, for those of you who are building along at home. 

Here’s what you’ll need:

-2X: 6-32 x 2” brass screws
-2X: 6-32 brass nuts
-4X: ¼-20 x 1 ¼” bolts
-2X: Ring style insulated terminals
-Piezoelectric BBQ igniter
-3’ of 1.5” inch PVC pipe
-18” of 3” PVC pipe
-3” PVC coupler
-3” PVC Female Threaded Adapter
-3” Clean out cap
-3” to 1.5” reduction Bushing (may have to use more then one bushing)
-2X: ¾ “ Tees PVC
-2X ¾ “ 90 degree elbows PVC
-20 “ of ¾” PVC pipe
-1X: ¾” Cap PVC
-roll of duct tape
-roll of electrical tape
-roll of masking tape
-Fuel (hairspray, starter fluid, brake cleaner, propane)

Tools

-Cordless drill
-¼ inch drill bit
-3/16 inch drill bit
-1/8 inch drill bit
-PVC Pipe cutters
-Hacksaw
-Utility knife
-Ruler
-Measuring tape
-Black sharpie
-Crescent wrench
-Pliers
-Wire strippers/crimpers
-Screwdriver
-PVC Glue
-Scissors

If you want a (much) more complicated, giant combustion cannon, check out this baby: http://goo.gl/Y35WI

I’ll be chatting on a Hangout today at noon PST...tune in and post a question or comment for us to discuss. And be sure to upload pics of your own cannon! 


***SAFETY NOTICE***
(you should read this part) 

Maintenance
Aerosol chemicals can gum up the inside of the cannon. Every few shots, clean it out with a rag and cleaner. The residue can also make the end plug hard to unscrew. If necessary, use pliers.

Safety and legality
During construction, don’t take shortcuts or substitute inferior materials. The vapors from PVC cement are flammable, so allow all joints to dry fully before exposing the gun to ignition sources.

When using the cannon, exercise extreme caution. Wear eye protection, and check the area in front of you before firing. Never look down the gun's barrel, or point it at anything you don’t want to hit. Excess fluid stays in the chamber and evaporates slowly, so you should always treat the gun as if it can fire. Check frequently for signs of wear, and never operate a damaged gun. Avoid contact with (or proximity to) the ignition path. 

PVC is more brittle in cold weather, so don’t use the cannon in temperatures below 60ºF. For added safety, wrap PVC elements in several layers of duct tape to minimize any possible shrapnel.

Neither the author nor MAKE assumes liability for your cannons or your actions.
Potato cannons and other launchers may not be legal in your area (even if it is legal to tote a 12-gauge down Main Street). Check with local law enforcement regarding the rules in your area, and obey them.
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