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My first spud cannon [Feedback/Advice appreciated]

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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My first spud cannon [Feedback/Advice appreciated]

Unread postAuthor: Zach1188 » Wed Jul 15, 2009 9:35 pm

Though technically not my "first" spud cannon, it is my first serious project. After building a small, possibly dangerous, underpowered, and poorly designed (ranch bottle as the chamber) spud gun, I decided to go to the hardware store and pay about $40 and do it right.

After doing research I found that combining PVC and ABS plastic is not a good idea as they will not glue properly, however the man at the hardware store convinced me otherwise. I purchased:

ABS:
2 Feet 4" pipe (1.5 feet used as chamber)
2 Feet 3" pipe (8 inches used for chamber "adapter")
10 feet 2" pipe (barrel, 5 feet used).

PVC:
4" end cap
4" to 3" reducer
3" to 2" reducer
2" male and female adapter (for breach loading/interchangable barrels)

Fuel:
(Works great, consistently. Held 1 - 1.5 ft from back opening, very quick tap on nozzle is usually perfect)
Image
Contains:
Diethyl Ether, Heptane, Propane, Iso-Butane, Carbon Dioxide

Ignition:
Piezo electric grill ignoter; 3 spark gaps.

Diagram:
Image
Blue indicates threaded joints, yellow indicates spark gaps

The result:
Far better than expected. Started testing with no projectile. Hit igniter, and a large fireball shot out of the barrel, and about 2 seconds later could hear a loud puff of air hit the metal shed about 25 feet from the end of the barrel.

Then tested with small potatoes, smaller than 2", so it was unfortunately not air tight. There was about a 1 cm gap between the potato and the barrel. Despite this, at 45 degrees the potato landed about 90 yards away. The cannon made a loud "THOOOMP" sound. Tested with about 7 of these potatoes, all went about the same distance.

Went to store and bought some large red potatoes (red potatoes are denser it seems), which were air tight in the barrel. Fearing of the off chance that it would land near the distant neighbors, I stood about 60 feet from the metal shed. I hit the igniter.....and my god it sounded like a shotgun. The recoil almost knocked me over, as I was expecting the usual small recoil. There was almost no delay between the crack of the cannon and the potatoes impact on the shed. My shed door will never be the same (its junk anyway :P ). Now I realize that potato would have reached my neighbors, and then some.

It's very consistent and reliable, thus far. If I have my hand in the wrong place, the piezo electric igniter sometimes arcs to my palm, annoying because then the inner spark is too weak to ignite the vapors. It feels very solid, however I am concerned with the PVC-ABS combination. It was glued using PVC primer and cement.

Future improvements:
- U shaped barrel, to make for a shorter cannon while maintaining barrel length
- Chamber fan
- Stun gun or flint ignition (Advice?)
- [Possibly] Propane with guage


Pictures:
Image
Image
Image
Random pictures


Image
The spark gaps, from outside. Ran out of black electrical tape :roll:


Image
Breach loading :D


Image
Full view with attached barrel
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Last edited by Zach1188 on Wed Jul 15, 2009 11:20 pm, edited 2 times in total.

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Unread postAuthor: theBOOM » Wed Jul 15, 2009 10:41 pm

Hm sounds like a good solid first build cannon. :D If you used pressure rated fittings AND pipe (nsf pw) then you are ok.. don't worry about your chamber being damaged... I havent heard of any problems from people mixing abs and pvc IF they are properlly solvent welded... Since your chamber is fairly big it was a good idea for you to use multiple spark points, I strongly recommend you buy a fan, it will improve your cannon's perfomance alot :twisted: .

For improvements.. I would make a hole new cannon if you want an over under design... Chamber fan , like I said you really should look into buying one... Stun gun ignition or flint ignition... Flint ignition is a nono, you would be better of making a camera circuit ignition... As for stungun.. if your current piezo isnt getting the job done then yes it might be a good option, but if your current piezo is getting it done why waste money that could be used to make other spudguns :D... As for metered propane... Like I said your chamber might be good for a SPRAy n SPRAY hybrid but... I wouldnt trust it TOO much as an advanced combustion, but that is up to you :roll:

Maybe some decent pictures :idea: :D
Again, nice job on a first build

Boom :twisted:
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Unread postAuthor: c11man » Wed Jul 15, 2009 10:48 pm

i know how much better that starting fluid is than hairspray so your doing pretty good. and presssure rated fittings dont mean squat if you are using abs in them. it might be ok with a chamberfan but a burstdisk would be pushing it
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Unread postAuthor: Zach1188 » Wed Jul 15, 2009 11:08 pm

Pictures added 8)

Thanks for the feedback. All parts are schedule 40, and the PVC is rated for 330 PSI. The ABS I assume is not pressure rated, so I'm not sure what it could handle before cracking.

I haven't really tried anything other than the starter fluid. It took me about 30 minutes of trial and error to get the perfect amount of spray figured out, but wow is it powerful. I used isopropyl alcohol and acetone (wasn't PVC :P) in my first cannon, and wasn't too impressed. I assume hairspray would be similar.

I was thinking of using a stun gun because piezo is a little annoying. It lights fine, 100% of the time, unless I put in the wrong amount of ether. But after about 50 presses, the button just "gives" as if theres nothing under the button but a spring. After rotating the button back and forth and messing with it, I can get it to "grab". If that makes any sense. Now, will a chamber fan increase performance, or just make ignition easier?

Edit:
Oops, I accidentally got my primer spill in one of the pictures :oops: I was trying to avoid that, going to sand that off tomorrow. Along with replacing that red tape with black. Or maybe white, to go with the PVC fittings.
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Unread postAuthor: inonickname » Wed Jul 15, 2009 11:42 pm

The two bell reducers are DWV. Asides from that, nice cannon. Some good improvements would be a chamber fan and spark strip, but the biggest improvement would come from an accurate metering system.

Nice work :wink:
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Unread postAuthor: THUNDERLORD » Thu Jul 16, 2009 12:03 am

...Contains:
Diethyl Ether, Heptane, Propane, Iso-Butane, Carbon Dioxide...


There's a way to easily remove the CO2. :twisted:
As well as seperating the ingredients also ...
Not sure if I care to add more info on that since some idiots inhale it...(ether is a knock out gas IIRC(?) too, so it's double stupid for dummies to inhale while getting a "Buzz" from the brain-cells buzzing away).

Saw a guy at a party doing such, and thought how (quadruple) stupid :shock: ...but also the spud type possibilites :wink:

Cool cannon!
Be careful with that starting fluid, it has more giddyup than gasoline,
Suppose that's why it starts gas engines and can also blow out piston rings. 8)

EDIT: Probably some of the ingredients are to keep it from breaking engine parts so my theory...seperated form, it's stronger. :twisted:
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Last edited by THUNDERLORD on Thu Jul 16, 2009 12:09 am, edited 1 time in total.
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Unread postAuthor: inonickname » Thu Jul 16, 2009 12:06 am

THUNDERLORD wrote:
...Contains:
Diethyl Ether, Heptane, Propane, Iso-Butane, Carbon Dioxide...


There's a way to easily remove the CO2. :twisted:


Limewater is a common test for carbon dioxide, though I don't know how high a concentration it could actually scrub from the gas. I don't think there's any CO2 scavengers.
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Unread postAuthor: Zach1188 » Thu Jul 16, 2009 12:31 am

Inonickname, the reducers are DWV? Are you sure? They were in Home Depot's PVC section in a SCH 40 PVC labeled box.

THUNDERLORD, is it necessary to remove the CO2? I suppose I might get some more performance but how much? And you're damn right it has more giddyup than gasoline :twisted: I put the end cap, which is likely the weakest point other than the potato, behind me (in firing position) for that purpose.

Edit: After consulting Google I guess DWV is a type of PVC?
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Last edited by Zach1188 on Thu Jul 16, 2009 12:38 am, edited 2 times in total.

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Unread postAuthor: THUNDERLORD » Thu Jul 16, 2009 12:32 am

inonickname wrote:
THUNDERLORD wrote:
...Contains:
Diethyl Ether, Heptane, Propane, Iso-Butane, Carbon Dioxide...


There's a way to easily remove the CO2. :twisted:


Limewater is a common test for carbon dioxide, though I don't know how high a concentration it could actually scrub from the gas. I don't think there's any CO2 scavengers.


...No CO2 scavengers, Hmmm...Stronger combustion fuel scavengers on SF's ? NO way!!! :roll:
CO2 Is NON-flammable what would "CO2 scavenging" be doing in a combustion thread?

Sounds like carbonated other stuff to keep it from blowing engines.
With other weaker flammables to balance it too.

BTW, another test for carbon dioxide is to read the label maybe???
It'd be more practical to "scavenge" CO2 from sodas if that had been the purpose...enough/too much said (for now).

Maybe this will help remind you to invert thoughts before jumping to conclusions?
...I got to rest, long day...Later. 8)

EDIT: @Zach1188: Srry for posting so soon after your reply, it went through before i noticed.
3rd reply here, Awesome, And welcome to SF's.
I wouldn't experiment with that fuel in PVC...think about it, gas engines have a fairly high hybrid mix and even un-altered, it can break them!!!
edit: (been known to sometimes break piston rings or bend piston rods) :shock: 8)
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Unread postAuthor: Moonbogg » Thu Jul 16, 2009 12:53 am

Are those holes drilled in the chamber? Holes should be drilled at the coupling areas for extra strength. The holes will weaken your chamber a lot like that. At least the chamber is ABS so if it does fail its not likely to shrapnel as much. Cool cannon though.
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Unread postAuthor: Zach1188 » Thu Jul 16, 2009 1:03 am

No problem, THUNDERLORD. Thanks for the welcome :wink: So I take it I made a good choice for spray 'n pray fuel?

Yeah Moonbogg they are. I was wondering about that, if it would weaken it significantly. I suppose I could have cut some more 4 inch ABS in fourths, lengthwise, glued it on and drilled through that. And thanks for the compliment!

Also for the over-under barrel, I was thinking of making myself an "adapter" for that. Basically making a 2 IN. "U" shaped segment, with a male adapter on the barrel end, and female adapter on chamber end. That way I can use the same barrel and breach load the same. Next time I will just make a coaxial cannon (w/ cutting barrel) similar to the BL-520. It wont be anything like the BL-520, but after seeing it the coaxial design looks very practical.
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Unread postAuthor: inonickname » Thu Jul 16, 2009 2:16 am

THUNDERLORD wrote:
inonickname wrote:
THUNDERLORD wrote:[quote]...Contains:
Diethyl Ether, Heptane, Propane, Iso-Butane, Carbon Dioxide...


There's a way to easily remove the CO2. :twisted:


Limewater is a common test for carbon dioxide, though I don't know how high a concentration it could actually scrub from the gas. I don't think there's any CO2 scavengers.


...No CO2 scavengers, Hmmm...Stronger combustion fuel scavengers on SF's ? NO way!!! :roll:
CO2 Is NON-flammable what would "CO2 scavenging" be doing in a combustion thread?[/quote]

Erm, you know what I mean by a scavenger don't you?

It's just a chemical that actively picks up another chemical; for example activated charcoal. A lot of scavengers will only scavenge for one thing; for example a chlorine scavenger. If I remember correctly the best chlorine scavenger can pick up 9 chlorine atoms. Though I don't think that there's any CO2 scavengers. (well, any feasible ones)

The idea would be to get rid of it, but I believe the amount of CO2 in there is basically insignificant.

I'm over 9000 percent sure that those are DWV, you can get rated bell reducers but they're redicuously uncommon, and for good reason. It probably wont go off on you anyway.

Edit: there is a commercially available CO2 and hydrogen sulfide scavenger, though that would hardly be practical..
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Unread postAuthor: Zach1188 » Thu Jul 16, 2009 2:43 am

I'm getting a little nervous about the materials I used to create the cannon. I have read DWV parts tend to fail. It appears both my PVC and ABS are DWV. My ABS is cellular core. I'm hoping in the event of a failure, the ABS will fail first and crack. Am I at serious risk here? Are there any signs before the plastics begin to fail?

Also does starting fluid damage PVC or ABS?
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Unread postAuthor: nsane-spuds » Thu Jul 16, 2009 10:21 am

Nice cannon!

Personaly, I really think the materials you used are fine. First of all, seems people get confused when it comes to DWV parts, DWV stands for Drain, Waste and Vent this simply means that pipe that is labled DWV is suitable for these uses and almost any pipe qualifies. So yes, DWV parts can be pressure rated and if you found yours in the pressure rated section it is very possible they are. Also, ABS is absolutely fine for combustion cannons in my opinion and if it does fail, no worries, it wil just crack.

Oh and definitly throw in a fan and a propane or mapp system, trust me, you wont be disapointed.
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Unread postAuthor: Zach1188 » Thu Jul 16, 2009 12:34 pm

Good to hear about the ABS. But I don't think the PVC is pressure rated, it says NFS-dwv on the edges of the fittings. Does that mean it's not pressure rated?
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