Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 58 users online :: 4 registered, 1 hidden and 53 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Project: 10 gallon

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
Sponsored 
  • Author
    Message

Bumper

Unread postAuthor: Technician1002 » Thu May 28, 2009 12:00 am

mobile chernobyl wrote:What type of bumper are you using? I've put alot more stress on that in my designs after a faulty bumper design caused a catastrophic failure on a 4" coaxal I had allowing the piston to shoot out the back of the gun.

The piston design I will be using is good amount different from your's however and I'm not too worried about cracking. I'll post a pic of it when completed.


Closed cell swim noodle. I wasn't too worried about cracking either. I thought my first was a manufacturing defect, the second, was a concern, the third a indicated a bad trend, and the forth was the last straw. I even babyed the last one and ran on reduced pressure, but it still failed. It didn't blow out the center the last time.

It's time for new material.

On the replacement of the Mouse Musket, I went to a QDV configuration and again used a swim noodle for the bumper as shown.
  • 0

Attachments
PICT249.JPG
Cutting diameter of bumper down to size.
PICT250.JPG
Parts of the breech, piston, bumper, pipe plug. Blowgun trigger not yet attached.
Parts1.JPG
Bumper assy can be seen in the replacement for the Mouse Musket after a coupling failure. PVC is brittle. This is the Marshmallow Cannon. Almost all PVC has been eliminated from high stress areas.
User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: mobile chernobyl » Thu May 28, 2009 12:34 am

good to see your having luck with pool noodles. I thought they were the "best thing ever" with my 1 gallon gun, but I had issues with it being sucked out along with the pilot air. I've switched to linear stacked rubber tubing, coaxial with the axis the piston travels on. works great with my "1 gallon" gun.

What do you reckon would be a decent weight for a piston in a 3" porting valve? the design I have now is alittle over a pound. I have about 1.5" of compressable bumper before "bottom out" if I allow for a 1.25" distance traveled of piston. I'm not sure of the time the piston would take to open but the force's are definately adding up, so a good bumper is definitely a high priority if I want to use this cannon more than a handful of times.
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: Technician1002 » Thu May 28, 2009 12:51 am

mobile chernobyl wrote:good to see your having luck with pool noodles. I thought they were the "best thing ever" with my 1 gallon gun, but I had issues with it being sucked out along with the pilot air. I've switched to linear stacked rubber tubing, coaxial with the axis the piston travels on. works great with my "1 gallon" gun.

What do you reckon would be a decent weight for a piston in a 3" porting valve? the design I have now is alittle over a pound. I have about 1.5" of compressable bumper before "bottom out" if I allow for a 1.25" distance traveled of piston. I'm not sure of the time the piston would take to open but the force's are definately adding up, so a good bumper is definitely a high priority if I want to use this cannon more than a handful of times.


Do you have a copy of GGDT? (Gas Gun Design Tool). It is good for this type of calculation. On a 3 inch a pound is reasonable and yes the force is very high. It is why I went with a metal valve body in this 2 inch launcher.
  • 0

Attachments
GGDT.jpg
Gas Gun Design tool attempting to match my performance graphs of the QDV t shirt cannon.
4 inch test.JPG
Metal tank 2 inch valve cannon. Test setup with 4 inch barrel and Poof foam ball.
User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: mobile chernobyl » Sun May 31, 2009 9:12 am

Technician1002 wrote:Do you have a copy of GGDT? (Gas Gun Design Tool). It is good for this type of calculation. On a 3 inch a pound is reasonable and yes the force is very high. It is why I went with a metal valve body in this 2 inch launcher.


Yea I quite frequently use GGDT for paintball design, great tool - I shared it with the community over at PBnation in the custom markers sub-forum and it caught on quickly.

It looks like I will be using 3 layers of coiled "radiator" hosing similar to that from a car. I'll loop them into a donut like shape, and stack three of them between the pilot chamber cap and the piston rear. I've been able to shave alot of weight off my piston and hopefully will have it done today.

My next priority will be designing a wheeled support stand. The biggest complication is incorporating linear bearings for around 1ft to 18 inches of travel and damping to allow recoil absorption.
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: Technician1002 » Sun May 31, 2009 11:13 am

mobile chernobyl wrote:
Technician1002 wrote:Do you have a copy of GGDT? (Gas Gun Design Tool). It is good for this type of calculation. On a 3 inch a pound is reasonable and yes the force is very high. It is why I went with a metal valve body in this 2 inch launcher.


Yea I quite frequently use GGDT for paintball design, great tool - I shared it with the community over at PBnation in the custom markers sub-forum and it caught on quickly.

It looks like I will be using 3 layers of coiled "radiator" hosing similar to that from a car. I'll loop them into a donut like shape, and stack three of them between the pilot chamber cap and the piston rear. I've been able to shave alot of weight off my piston and hopefully will have it done today.

My next priority will be designing a wheeled support stand. The biggest complication is incorporating linear bearings for around 1ft to 18 inches of travel and damping to allow recoil absorption.


Linear bearing is easy. Repair couplings on metal pipe. It gives good travel. For recoil, a set of screen door closers work well. On recoil, it pulls springs to take the energy at high rate with no damage (unless you over travel them. Size properly). On return forward, the energy in the springs is dissipated at a reasonable rate for no damage.

Linear slide.. Check. Recoil damper, check. For larger stuff, car struts work well.

Because the peak force in an air cannon is much less than a solid combustion (military) often recoil suppression is not needed if the support is built to hold the peak force without movement. For example, on my 2 inch cannon with a 3 inch barrel. A mount that won't move with about 700 lbs push will work well with anything I can load into the 3 inch barrel at up to 100 PSI. The peak recoil force won't ever exceed about 700 lbs. Rubber tires on a mobile artillery unit is often all that is needed.

Here is a fine example of a exceedingly large cannon using tires. I wish this were mine. Nice cannon.. Anybody we know?
[youtube]http://www.youtube.com/watch?v=YoIy4GkaIZQ[/youtube]

That cannon packs a very serious punch.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: mobile chernobyl » Thu Jun 04, 2009 4:56 pm

I was thinking more along the lines of a howitzer, and looking around I've found my inspiration... The M119

Image

Here's an updated view of my CAD modeled gun (now like 99.9% accurate to scale)

Image

It works!! I fired it for the first time yesterday, and at only 10psi I'm happy! The sprinkler valve wouldn't "trip" at that low of a PSI but I put a 1" ball valve on it and it unleashed holy hell in my garage lol.

Heres a pic of the piston and bumper system, including the back plug, and some volume reduction going on (shaved down 4X4) in the pilot volume area.

Image
Image
Image
Image

The tubing has notches for 2 reasons - The notches allow it to fold in a circle without folding on itself. The size of the notches also dictate the "hardness" of the bumper. I have the tube with large notches directly behind the piston, and the tube with smaller notches behind that one to kind of create a "progressive" bumper effect, and hopefully it will work well at higher pressures. The bumper this way is about 2" unsquished.


Here's the scissor jack I will be rigging up to control angle of the muzzle

Image

I am designing the "howitzer" stand as I type this, and will hopefully be able to pick up the metal and weld it up this weekend, I really want to fire this bad boy!!! I'm thinking the first round of shots will be basically a 24 pack of water from the grocery store, as it fits very nicely in the 3" sch 80 barrel.
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: thedeathofall » Thu Jun 04, 2009 5:44 pm

This would be a great time to create a blowforward breech. Combined with a decent compressor, you would have the biggest, baddest, semi automatic, long range paintball/waterballoon artillery piece known to mankind!

That would be like the guided missile system of modern paintball.
"It hits when no one is expecting it, and it kicks more butt than Arnold in the Terminator." :roll:

Seriously though, with semi auto technology at you fingertips, this gun would go from great, to AWSOME!

Just my $2 ($0.02 doesn't seem like it is worth enough here :wink: )
  • 0

"I'm spending time without a gender for tax reasons. It's great if I get hit in the groin, but a total nightmare in the bathroom."

-Rag


Obsequium parit amicos; veritas parit odium.

-Cicero

thedeathofall
2nd Lieutenant
2nd Lieutenant
 
Posts: 213
Joined: Tue May 06, 2008 10:43 pm
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: Technician1002 » Thu Jun 04, 2009 6:59 pm

mobile chernobyl wrote:
Here's the scissor jack I will be rigging up to control angle of the muzzle

Image

I am designing the "howitzer" stand as I type this, and will hopefully be able to pick up the metal and weld it up this weekend, I really want to fire this bad boy!!! I'm thinking the first round of shots will be basically a 24 pack of water from the grocery store, as it fits very nicely in the 3" sch 80 barrel.


Since you weld, have you considered using a propane tank instead of using PVC for the chamber? A tank can be hidden behind a blast shield down between the wheels and provide a nice business end profile. It would be safer for the operator at higher pressure.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: mobile chernobyl » Fri Jun 05, 2009 5:49 am

TDOIA - I've worked on a few semi-concepts, and my conclusion is they work best with small volume and higher pressure (paintball gun) with my current air source (compressor). I'd need a high volume air source to make a large scale semi feasible with any reasonable amount of rounds per minute.

Technician - Propane tanks are a good idea, however this is like my "signing off" project for PVC so I won't change anything on it. My next large scale gun, if using metal, will most likely just use a homemade pneumatically actuated 4" butterfly valve, as the butterfly valve alone can be had for like $60, and they are rated for 200WPSI (on the low scale). A good portion of the pumpkin chunkers all use butterfly vales, and when your dealing with large volume, and long barrels, the slightly slower actuation of a butterfly valve versus a piston (which on a 4 inch porting gun will weigh quite a lot!!) will not have any great effect over the length of the barrel (usually 15' or longer)

Propane tanks, water heater tanks, etc are all valid ideas however, and with my current job as a tig welder on pressure vessels (300PSI) I trust my welds. I'd simply just weld a 4" flange to whatever air reservoir I'm using and voila - A big ass spud gun lol.
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: Technician1002 » Fri Jun 05, 2009 10:14 am

mobile chernobyl wrote:TDOIA - I've worked on a few semi-concepts, and my conclusion is they work best with small volume and higher pressure (paintball gun) with my current air source (compressor). I'd need a high volume air source to make a large scale semi feasible with any reasonable amount of rounds per minute.

Technician - Propane tanks are a good idea, however this is like my "signing off" project for PVC so I won't change anything on it. My next large scale gun, if using metal, will most likely just use a homemade pneumatically actuated 4" butterfly valve, as the butterfly valve alone can be had for like $60, and they are rated for 200WPSI (on the low scale). A good portion of the pumpkin chunkers all use butterfly vales, and when your dealing with large volume, and long barrels, the slightly slower actuation of a butterfly valve versus a piston (which on a 4 inch porting gun will weigh quite a lot!!) will not have any great effect over the length of the barrel (usually 15' or longer)

Propane tanks, water heater tanks, etc are all valid ideas however, and with my current job as a tig welder on pressure vessels (300PSI) I trust my welds. I'd simply just weld a 4" flange to whatever air reservoir I'm using and voila - A big ass spud gun lol.


Nice. I have been reaching the same conclusion that smaller higher pressure is the way to go for many smaller projectile cannons.

On the topic of pumpkin cannons and butterfly valves, they are a good match simply because the projectile is relatively soft. Due to the launch speeds nearing mach 1, most casual observers assume high pressure. This is false. High pressure and high cross section would make mush and produce the "Pie in the Sky" shots that don't count. For this reason pumpkin cannons are low pressure with a very long acceleration distance (Long barrel) To feed this long large volume a large chamber is required. When a valve is first opened, the chamber pressure is at it's peak, so to limit the peak acceleration a slower valve is desirable. Most people do not know that most pumpkin cannons use less than 35 PSI. Higher pressure creates broken pumpkins.

With the pumpkin cannon theory out of the way, is there any reason to stick with a butterfly valve? A high pressure cannon will use a much smaller tank, shorter barrel (under 20 feet), use harder projectiles, and can benefit from a faster valve. At near supersonic speeds the pressure wave off the edge of an open butterfly valve is a concern in terms of valve coef.

Butterfly valve, larger cannon :idea: Are you planning on building a pumpkin cannon?

I was playing with GGDT again an it looks like a 4 inch valve on a 200 PSI vessel feeding a 3 inch barrel (toolie style valve to barrel cone) off a piston valve will be able to exceed SOS by a large margin. I'll play with that more after I collect data off the current 3 inch project. I may even be able to get the small marshmallow cannon supersonic using the 1 inch valve to feed the 3/4 inch barrel with 3 gram projectiles at 200 PSI. (mini marshmallows & sabot) I'll play with it more later.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: thedeathofall » Fri Jun 05, 2009 11:03 am

TDOA - I've worked on a few semi-concepts, and my conclusion is they work best with small volume and higher pressure (paintball gun) with my current air source (compressor). I'd need a high volume air source to make a large scale semi feasible with any reasonable amount of rounds per minute.


Haha ya thats what i figured. I still think that semi would be pretty awsome though.
  • 0

"I'm spending time without a gender for tax reasons. It's great if I get hit in the groin, but a total nightmare in the bathroom."

-Rag


Obsequium parit amicos; veritas parit odium.

-Cicero

thedeathofall
2nd Lieutenant
2nd Lieutenant
 
Posts: 213
Joined: Tue May 06, 2008 10:43 pm
Reputation: 0

Unread postAuthor: mobile chernobyl » Fri Jun 05, 2009 4:08 pm

Technician - The reason I'd be using a butterfly valve is because it would be a 4" valve (or bigger) monster cannon. That is of course if I find any need to make one. I'm still in college right now so I don't have the ability to store the gun in one place easily. It would have a 15' barrel at least, so like we were saying, actuation time is not of highest concern.

For any other higher pressure valve, if dealing with metal, I'd most likely use a spool valve, as I've developed alot of them with guys on PBnation.com for custom guns. I want to develop a semi sometime in the future but will probably wait until I get a lathe, or get lathe access again to make one as I want to be able to develop some of the valve idea's I've worked on at PBnation, and they will require higher tolerance control (+- .003") than a simple homemade lathe or mill will allow. With those designs I'd most likely go with a chamber pressure between 300-500 depending on the chamber volume. But some of the Spool valve designs I have are certainly pretty cool, and efficient, only requiring 1 normally closed solenoid valve to operate a semi automatic - normally closed bolt spool valve design, with a ROF around 13-15 RPS easily.

for now I just need to finish Cadding out my spud gun stand... which unfortunatly will have to wait another week as this weekend did not work out right sofar, o well I'll be able to refine my design at least.
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: mobile chernobyl » Sun Jun 07, 2009 11:41 pm

A little eye candy update with some of the (close to) finished drawings of the stand.

I veered away from the simple howitzer design, and the recoil absorption design, as these just don't seem that necessary when all the forces are run, and the gentle acceleration of air projectiles versus solid fuel is taken into account.

Without further wait, here are some preliminary shots of the stand without wheels and other features, like the jack to elevate it.

I used some of my knowledge in kinematics to develop a linkage to provide a little bit better elevation control (Mainly to achieve 45 degrees angle without having to place pivot so high - to anyone with knowledge in kinematics - the Instant center of this design, while floating as with any 4 bar linkage, is actually above the gun by around a foot at 45 degrees, making the design very compact at completely level setting), and to take advantage of the jack stands "leverage curve"... yea i won't get into that lol.

Image
Image
Image
Image

Keep in mind that at 45 degree angle of inclination, the barrel tip is over 10 feet off the ground.

More to come later in the week, with fabrication starting this weekend. Sleep now though...
  • 0

Last edited by mobile chernobyl on Sun Jun 07, 2009 11:56 pm, edited 1 time in total.
User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

Unread postAuthor: thedeathofall » Sun Jun 07, 2009 11:54 pm

That is going to be pretty sick. To bad you have to lower and re-aim every time you reload.
  • 0

"I'm spending time without a gender for tax reasons. It's great if I get hit in the groin, but a total nightmare in the bathroom."

-Rag


Obsequium parit amicos; veritas parit odium.

-Cicero

thedeathofall
2nd Lieutenant
2nd Lieutenant
 
Posts: 213
Joined: Tue May 06, 2008 10:43 pm
Reputation: 0

Unread postAuthor: mobile chernobyl » Sun Jun 07, 2009 11:59 pm

With this gun rapid fire is the least of my concern.... lol I'll make that first shot count so I won't need to take many (if any) more. And I'll definatly know when it hit.

This gun has over 500cubic inches more volume than the "spudtech mega launcher" and also has over an inch extra effective porting area, meaning it WILL be effective lol.
  • 0

User avatar
mobile chernobyl
Colonel
Colonel
 
Posts: 732
Joined: Sun Dec 03, 2006 11:53 am
Reputation: 9

PreviousNext

Return to Pneumatic Cannon Discussion

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'