SpudFiles

I stumbled upon this site as well as spudtech and a bunch of other potato cannon sites, and decided it would be fun to make one, so I did a bunch of research while waiting for school to get out. I have finally finished and tested my potato cannon to about 30 psi. I have only gotten one shot off due to short time, but it managed to break one of those aerosol can caps on a wall (realize that this is inside, so I am not shooting anything that could do any damage.) so here are some pics. And this is my first cannon, so call me a wimp, but the valve is a mauler purchased online. I will post more pics tomorrow once I have tested it to higher psi and moved it outside and shot something worth shooting.

The barrel is 12 feet long, though in three parts so it can be taken to 4, 8, or 12 feet. I believe the C/B ratio is around 1:1.8 or something.

Video:
I managed to get a golf ball through 1 inch (2 .5 inch plates) of plywood at less than 50 psi

that thing is quite big. is there a problem with your sprinkler valve, why is it open like that? are you going to make a mount for it, because it looks way to big to hold. you should also make a barrel support, so it doesn't put so much stress on your elbows and T.

I couldn't find a blowgun valve, so i just stuck a .5 inch ball valve in it. It works fine. i will either make a stand, or if I am too lazy, just stack books and other stuff to hold the barrel up.

edit: oops, didn't understand your question, the sprinkler valve is open because these photos were taken before shooting, and I hadn't closed up the modded valve.

Whats the barrel and chamber diameter?
Nice cannon, good that your utilizing most of the air pressure with the long barrel so no power wasted.

Thanks,
The chamber is 4 inch pvc rated to 220 psi and 4 feet long, barrel is 1.7 inch golfball.

You should add a barrel support which will support the barrel and help keep all the strain off the tee fittings when you pick it up.

Yeah, that would be nice, I have a bunch of acrylic plates lying around somewhere that would work pretty well as supports. But tomorrow I'm just gonna shoot stuff... done enough work on it today.

Also, If I balance it perfectly on a tripod, I could aim it effortlessly...

Very very nice, but it would be a great idea to give the barrel some support before you go shooting it. The recoil will put that elbow under a lot of stress, and it would really suck if it broke. Other than that its an excellent cannon. Great work!

that thing is beautiful. especially for you're first . you sir are my new hero.

pretrty formidable for a first effort, though it certainly could use a bit of support as greater pressures and heavier projectiles will increase the recoild forces considerably and could potentially damage the cannon.

A little efficiency point, there's too much dead space behind the piston, you should mount the sprinkler valve directly to the back of the piston, and epoxy your filling schrader directly to the fitting - there's no need to close it off with a ball valve.

this is the (second) best first gun i have ever seen. i have t ogive yuo second because of schmanmans swat you should have just made the piston valve because when you first make a piston valve and it works you are extatic..

You could also reduce pilot volume by using pipe nipples and threaded fittings instead of male adapters.

Does dead space in the pilot area make a difference?
I noticed that It did have a pretty large space between time of sprinkler valve going off, and time of firing... like around one second

and spudthug, I was pretty ecstatic that it worked anyways

Oh yeah! If you mounted your valve directly to the back of your piston like JSR said, it should actuate instantly. The seal on your piston can't be to good if it takes that long to fire though.

Okay I finally shot something. An arrow, with a plastic bag sabot. It went thru a tube that I had laying around, and the best part is... I got it on video!
so I'll post when I figure out how.

EDIT: got it...
you might notice that the barrel comes off, that is not a problem, I haven't gotten around to glueing the barrel to the valve fitting. I'm still debating whether to get camlocks or put some other finesse on it.

EDIT: this is 33 psi and 1/3 of the barrel, my parents don't want me going over 35 psi while they are not there...