Same way you would rifle a steel barrel with a rifling cutter. Did the writer of the article go to school with Al Gore? there is no “e” in POTATO

Nobody spelled “potatoes” wrong in this article, and neither did Al Gore. Perhaps Hacksaw is unaware of plurals and the fact that Dan Quayle is the one who famously corrected a student for properly spelling potato.

To Hacksaw:

“Did the writer of the article go to school with Al Gore? there is no “e” in POTATO”

Error 1 to the writer of the article.

Error 2 to you. Dan Quayle is not spelled A-L G-O-R_E.

It always bothers me to see the low quality/dangerous air cannons that appear here, especially in contrast to the usual amazing craftsmanship that is the standard here.

Even _pressure rated_ PVC is not designed to carry pressurized air, just pressurized water, (Pressure is pressure for the purposes of material failure point, but the energy contained in a volume of compressed air is much higher than a volume of water because it is far more compressible) though that in itself isn’t terribly damning.

However the reducers that they are using aren’t even pressure rated, they are DWV rated (drain/waste/vent), these are cell core, not solid core PVC and are dangerous to use in pressure applications.

Safety considerations aside, the use of a solenoid actuated sprinkler valve is severely limiting their performance. At the very least modding the valve to be pneumatically actuated would make the valve open perhaps 10-20 times faster.

Additionally, sprinkler valves are chamber sealing diaphragm valves and limit flow quite a bit. If you need a drop in commercial solution QEVs are leagues better and may actually be even cheaper than the sprinkler valve. If you are willing to spend an extra hour on construction you can easily build a piston valve (with no machining or special parts required, just some creativity) that will have millisecond opening times and will have no flow obstructions.

A higher performance valve will enable lower operating pressures (maybe as low as 15-20 PSI) and a much smaller pressure chamber (maybe 4 or 5 times smaller than what they are currently using). This means greater launch frequency, increased operating safety, and a far cheaper/quieter compressor.

Those interested in serious design/construction of air cannons should check out an excellent tool called the Gas Gun Design Tool (GGDT). Just google GGDT, it’s the first result, or see http://www.thehalls-in-bfe.com/GGDT/

Check out SpudTech.com they have rifled pvc barrels.

@andrew I know the guys that worked on this and they didn’t calculate z-distance based on y-axis height. They used the x-axis offset as you said, where did it say they used the y-axis?? Also, it did try to predict the future route, I’m not sure the video does a good job at showing that, however.

Also, they aren’t mechanical engineers and built everything themself so I guess you can’t really blame them for not building a completely up to par propulsion system.

@userjjb –

You have to remember that a sprinkler valve is the most common, easily accessible electronically-controlled valve. While the valves you mentioned would increase performance greatly (as you said), they can’t be electronically controlled as-is.

Another suggestion would be breech loading. Having to ramrod projectiles down long barrels is time-consuming. (even better would be to make it semi-automatic)