The PVC Air Cannon is made for all your launching needs. I'll do my best since this is my first instructable. To construct it you need the following materials:
Note: To build this cannon, you can use different PVC parts (couplings, bushings, adapters) than the ones I used. They just have to start from the valve up to the 3" diameter PVC.
-5.5' of 3" PVC pressure rated (schedule 40)
-2 of 3" DWV couplings
-2 of 3" by 1.5" flush bushings
-1 of 3" repair coupling
-2 of 1.5" by 0.75" PVC bushings
-1 of 0.75" FP ball valve fpt 600 psi lf (brass valve)
-2 of 0.75" PVC male adapter
-1 of 3" PVC cap
-reasonable amount of Teflon tape
-reasonable amount of PVC cement/primer
-less than 1' of 0.75" PVC pipe
-Metal tubeless tire valve
-Circular saw or hacksaw to cut PVC
-Drill to make hole for tire valve
Step 1: Plan/buy Your Parts
Like I said in the earlier note the PVC parts must start from the brass valve and up to the 3" PVC. You can buy probably buy these parts at your local hardware store: Home Depot, Lowes, Ace. My design is in the image above.
Step 2: Cut Pieces to Length
For the barrel I cut the 3" PVC to 4 ft long and the air tank to 1.5 ft long. You may also have to cut the 0.75" PVC to your desired length. About 4 to 5 inches long is good.
Step 3: Glue Your Cannon Together
Use your cement/primer to glue the parts together according to the diagram. Teflon tape should be used to connect the brass valve to the 0.75" male adapters. The pictures just show all the details of cementing/priming. Also, drill a hole in the 3" cap according to how big your tire valve is.
Step 4: Final Result
The picture shows how it should look like in the end. The projectile for the cannon should weigh at least a pound and should fit down the barrel tightly, barely letting air through its sides. I taped a water bottle to a foam cup reinforced with duct tape.
Step 5: Filling the Air Tank
To fill the air tank, you can either hand pump it or can use a tire inflation machine. I got it up to 80 psi. I don't think you should fill it up any higher than that.