Air-powered toy mortars?

[MatthewVanitas]

Greetings. I was recently walking through my local college campus, and saw a gaggle of teenagers and a couple guys in cammies setting up gear along the green. Said gear looked rather like makeshift mortars, which turned out to be exactly the case.

Apparently the teenagers (highschoolers) were there for some kind of summer engineering camp, and some Air Force aeronautical eng types came by to teach a class on aerodynamics.

They brought along a few "mortar" sets, consisting of a wooden frame, pressure tank w/ bicycle pump, PVC cannon-tube, etc. The kids built tubular projectiles from rolled plastic, added Dixie-cup nosecones and plastic fins. The plastic body of the projectile fits the external diameter of the cannon-tube. The tank is then pumped with the handpump, pressure read off the gauge, tube elevated by hand, then a release lever pulled to launch. They were aiming for hula-hoops lying flat in the grass, and getting maybe 50-75m of range with these 30" projectiles.

First off, I'm amazed that the U would let them do that on a green criscrossed by sidewalks and wandering students. Cool, but seems like the kind of thing that would cause bureaucrats to fret. Chance of injury is pretty darn low, but still...

Anyway, anybody ever built such a creature, or have plans available? Not any more range than just throwing a football out on to the green, but certainly more novel.

Just thought this would amuse a few THR folks out there, take care.

-MV

 

[Third_Rail]

Rather like a pneumatic potato gun, isn't it...


Seems pretty straightforward to build. I'll look around for schematics.

 

[nomadboi]

I've seen people make similar things using hairspray as fuel and a bbq lighter system (push button) as ignition/trigger. Launched a potato a couple hundred feet.

I'd be interested the the bicycle pump to pressure tank thing, if anyone knows how to make that kind of system work.

 

[fletcher]

My friends and I have constructed "potato cannons" before, which we fueled with engine starter.

We just took a 4-inch section of PVC pipe (about 2 feet long), then put a threaded end/cap on one end. On the other, there was a 4" => 2" coupling. The "barrel" was about 4 feet of 2" PVC. Drill hole in larger PVC and insert a piezoelectric grill starter (make sure the contacts are close enough to produce a reliable, consistent, spark). Run potato down barrel with broom handle, use a quick spray (~.5 seconds) of engine starter, quickly replace cap, and fire.

These things have had endcaps blow off and break before, so it's all at your own risk, of course

 

[RyanM]

I've built a pneumatic potato gun before. Fully pumped up, it can generate up to 400-500 ft-lbs of energy at the muzzle. Basically just an air tank and a barrel, with a solenoid-actuated sprinkler valve in between. I recommend Rain Bird valves if you're building a sprinkler valve gun. Those require an actuating current of 5-6 volts and a holding current of 1-2 volts, and have an operating pressure up to 150 PSI. Most other valves need 20+ volts to actuate and 10+ to hold, and only go up to 100-125 PSI.

Power on pneumatic guns is greatly increased over a combustion gun. Combustion of aerosol-air mixture generates a maximum of 10-15 PSI, while propane-air can approach 20 PSI. In comparison, a sprinkler valve pneumatic gun can operate at anywhere from 90 to 140 PSI, depending on the rating of your valve, how good your pump is, and how much you weigh (if using a manual pump).

Despite the increase in power, pneumatic guns are actually safer. PVC and PVC cement are not that compatible with a lot of the chemicals found in aerosol sprays, so the integrity of the plastic slowly degrades over time. The only safety issue with pneumatics is that firing will decrease the temperature of the tank, and PVC becomes brittle when cold. Simple solution is to wait a minute or two between shots.

 

[Harry Tuttle]

my Thumper:

it will shoot a nerf mini vortex rocket ~100 yards

 

[Azrael256]

I've seen the PVC types with the sprinkler valve at gun shows. It's a really simple device. Probably costs about $20 to build. It's just a length of 4" PVC, a cap, a couple of fittings, and a valve. Slap on an air fitting to the capped end... oh, and you'll need to paint it green. The guys at the gun show painted it green.

Harry, two things: where did you get that, and how far will it shoot a barbie doll?

 

[Harry Tuttle]

i could set up a barbie at 100 yards and see if it holds MOA


A successful barbie launch would require a pool noodle wadding.
Since barbies are not very aerodynamic, i doubt she would travel more than 40 yards.
If i engage a charging luan interior door from 10 feet, i bet i could fire barbie straight on through to the other side.

we prefer launching widdle stuffed bunnies,
but a sabot loaded with barbie heads might be good for a chuckle

http://www.bp-usa.com/weaponry.htm

this is a good set of homebrewed plans:
http://www.qsl.net/wb6zqz/csv19/

i have some reservations with cavorting about hill & dale with a pressurized PVC chamber

 

[Chrontius]

Anyway, anybody ever built such a creature, or have plans available? Not any more range than just throwing a football out on to the green, but certainly more novel.

Yep. The Dragon-Lance is a simple, robust, and quite powerful; I'd guess 5" gelatin penetration on a 2" steel cannonball. It's a five-foot length of schedule 40 (solid-core) PVC cut at the 2 foot mark, and a 2" ball valve inserted at that point. The short end was capped with a cleanout cap, with a drilled-in Schrader valve just in front of the endcap. Pipe's good to 150-200 PSI, endcap somewhat less; I figure it makes a good controlled critical failure mechanism -- easier to keep that pointed in a safe direction when charging (up to 100 PSI) than dodge flying PVC shards.


Some considerations:
Dixie cups with the rims removed make great pusher sabots.

At 25-30 PSI, it'll lob a marshmallow hundreds of feet, or a padlock about fifty. Straight up.

Use a foot pump, you can get to 100, as opposed to a hand pump at 30ish.

Watch where you're pointing that thing; at 100 PSI we're into firearm energy levels.

A dragon-lance can be built for $20, if you're not interested in having a chrome valve assembly. Less, if you've already got cleaner and cement.

Don't shoot it for (ideally) 72 hours after assembly; 24 is probably safe, but it's better safe than hospitalized.

These things are great fun; pretty soon you'll catch yourself designing field artillery. Post pics! ^_^

 

[thorn726]

the funny thing too- potato guns are actually mentioned in CA law, and are Legal! , as long as you dont shoot flaming/ exploding objects, and use it basically in accordance with regular shooting rules, you can make one

 

[armedcitizen]

Check out the book, Backyard Ballistics by William Gurstelle. Amazon has it here:

http://www.amazon.com/exec/obidos/t...103-8259937-4763065?v=glance&s=books&n=507846

but check your local library. Mine had a couple copies.

Also, I know the Cub Scout handbook had some sort of bike pump thing that would send a two litter, water filled pop bottle pretty high.

 

[Kaylee]

Harry.... you can launch little pink bunnies??? That ROCKS!

dang... I want one...

 

[308win]

potato guns are actually mentioned in CA law, and are Legal! , as long as you dont shoot flaming/ exploding objects

Darn, guess I'll have to find something else to do with my cooking.

 

[MikeIsaj]

Barracks Cannon

I recall making Barracks cannons while in the Marines. A tennis ball is the same diameter as a pringles can. Tape 2 - 3 end to end with duct tape. Use a soda can on the bottom with the pull tab opening facing into the pringles can and a small hole on the bottom. Squirt lighter fluid in the soda can and shake to vaporize. Load a tennis ball, touch a match to the hole in the bottom of the can and watch the ball go.

Had a lot of fun with these, on a friday night between paydays, in 29 Palms. How we never hurt anyone I couldn't tell you.

 

[dfaugh]

Chek out the Spudgun Technology Center

http://www.spudtech.com/

 

[chromatix]

air cannon / mortars

I build 40 and 150mm air cannons for projects in the uk.

the first prototype 38mmX18" tube i built fired a pingpong ball full of paint 200 yards and the 40mm production model will fire a sanded down golfball 1200yards.

anyone wanting more information or a couple of photo's please email me

[email protected]

this is a 40mmx8ft high velocity aircannon installed on an AR432 APC

late addition: the muzzle velocity of this cannon at standard working pressure (not 100% overpressure circa 300psi) is 576feet/second on the chronograph, OH!, and did i mention . . . . . we have THREE of these and offer tank battles in the UK with paint rounds?

 

[Preacherman]

I'd hate to get in the way of that golf ball!!!

 

[ckyllo]

ideal for a 1200 yard fairway
FORE
would let that guy play threw!

 

[Harry Tuttle]

sweet cannon, chromatix

theres a bunch of air tankers over here:
WARPIG Tank forum
that would love to hear more...

i've LAWs hunted this tank:

it runs a hand cranked 6 shot revolver

theres a 230 fps cannon inside this Ballista:

 

[GunnySkox]

Chromatix, that's approximately the coolest thing I've ever seen.

Mr. Tuttle, many of the things you've posted tie for second place (don't feel disheartened. Ain't much you can do when the competition is an IFV)

~Slam_Fire

 

[chromatix]

hey harry, you per chance own/work on a paintball site too?

 

[Gordy Wesen]

I made a 2" tubed potato gun and find I get 300 yards with Limes and Right Guard. Maybe I'll try starting fluid next.

 

[chromatix]

when building these mortars, i found the fundemental flaw being how fast the valve moves (or dosent move) and i eventually stumbled across a device that had a simple diaphram valve in it, you pass air thru it to the dump tank and it seals the outlet, you let the feed go and the diaphram jumps back and dumps the whole contents of the dump tank into the breech, we have managed to achieve discharge of an 8 litre air reciever 'dump tank' into the breech from 150psi to 0psi in well under 1/10th of a second which is what mekes these so potent.

we have not successfully fired a potato yet because they always seem to dissintigrate about 100yds out of the muzzle, might try carving a point on them next. the most successful round so far is a milled down synthetic bowling pin ( a 'twister' as they are known and hated in the bowling community ). this is a lump of polycarbonate capable of rebounding a 144 grain HV round out of a rifle and therefore makes a mess when it hits (milled grooves in at one end and put 2 o-rings in then milled a point on it)

ill drop some more info on when i get time.