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Picture of Prototype Dual Chamber Potato Cannon
Ok so u might be wondering thy yet another potato gun design here on indestructibles. Well this is not ur typical spud launcher but its also not the most advanced granted it will evolve into one by the time its finished.
This gun is less than half the sive of the final gun with only a 1" barrel ( the finished project will have a massive 3" barrel), but thats ok because its only realy for test perpouses. Test perpouses? U might ask, and the answer would be most defiantly due to the fact i have never seen all the "advancements" that will be in the final gun.  Heck i haven't seen some of the mods im trying to cram into this one gun.
First off u will notice it has 2 combustion chamber let that sink in for a sec....... yes its a crazy cool idea... little harder to make work. but that is what this wos fore after all. im not going to lye and say this is the most BA potato cannon ever but i will say it has the potential to be one of the most extreme guns ive seen. (yes even this small prototype) I can say this because launching from just one chamber i can put grapes thru my chain link fence and about 50 yards onto a wooden fence and make them dissapear.
The reason i say only one chamber is because i have had issues getting constant fuel supply to both chambers usually ill have one chamber way rich and the other spot on. i have had a few test fires with both chambers firing correctly and when they do the lack of barrel is disturbing. (with the 2' barrel it still produced a 1' flame out the end with just one chamber about dubble as u would expect with both chambers) so with all that sad i have the instructions for the small prototype here i will be building a larger one with all the components of the big one next ei, metered propane, chamber fans, support system, and a full length 0.6:1 c:b barrel. all this will be to see just how impossible for me or possible the full size gun will be before i actually make it.
With all that sad if yall do make this gun please share ur experience with me and maby we can make this a nice little potato launcher that can be made for under $50 (so far ive spent only $30 on mine)
 
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Step 1: Parts List

Picture of Parts List
ok so u have shown a little intrest in this project so now ill let u know the causts and parts list
all these parts were sorced from my local home depot prices are ea. (and total per part w/ total at the end)

1 - 1" non threaded t                                             0.62   (0.62)
2 - 1" threaded 90 deg elbow                             1.21   (2.42)
2 - 2" cuppelings                                                  0.86   (1.72)
2 - 1" non threaded 90 deg elbow                    0.48    (0.96)
2 - 2" close out caps                                           0.82    (1.64)
2 - 2" close out cap adaptors                            1.18    (2.36)
2 - 2" flush mount 1" adaptors                          1.78    (3.56)
2 - 1" * 24" pvc pipe                                             1.67    (3.34)
1 - 2" * 24" pvc pipe                                             3.70    (3.70)
1 - battory opperated grill ignitor (walmart)  17.65  (17.95)

                                                                               total     (38.27)

i origonaly sorced a solid state grill ignitor from home depot but before i even had the spark gaps adjusted the cheap thing busted so i ran to walmart witch wos closer and cheaper and sorced a battory opperated one for the replacement caust amlost of the solid state one from home depot

its important to try and use solid core pvc i cant stress this enouf ive made about a dosen high power spud guns from this stuff and never once had a fracture or miss hap due to falure of the pvc

Step 2: Chamber Pipes

ok so in this step we will make the 2 2" * 12" combustion chambers
  first u will wont to take your 24" 2" pipe and mark it at 12" and cut it
  now that u have 2 12" 2" pipes the messy part starts in a extremely well ventilated area apply a light amount of cement to the inner portion of one side of the 2" coupling
  next we will insert one of the flush mount adapters into the glued side of the coupling be careful to make sure the adapter is fully inserted in the coupling and its squaire
  after that is done apply some cement to the other inside of the same coupling and insert one end of the 12" pipe again making sure the pipe is fully inserted and squair
 next apply some glue to the non threaded side of the close out cap and slide the opposite end of the same 12" pipe again making sure its fully inserted and square... seeing a pattern here yet lol
  after that all that is left is to lightly screw in the close out cap
  u have just completed one of the chambers rinse and repeat for the second
 

Step 3: Pluming

Picture of Pluming
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IMG_0384.JPG
Ok this part is prob one of the hardest parts. (well for me it wos atleast)
first thing we need to do is figger out how much pipe we need to connect all the elbows since there all femail ends
i mesured from the little lip that stops the pipe on the inside that will tell me how deep the elbows are so ad up the 2 mesure ments (one form each elbow to be connected) and that will tell us how big are peaces of pvc will need to be
my elbows mesured at about 1" so my peaces needed to be 2" long each
next u need to figger out how many peaces of pvc u need for my setup i needed 4 one for each elbow comming off the chambers and one for each of the elbows going to the t
so now that all that complacated math is out the way i messured out 4  2" peaces of 1" pvc pipe and cut them apropetly
after that its just a matter of glueing all the pipes together. although this can be a little tricky since u neet to make sure everything is 90 deg from each other
to do this u will take one of the 90 deg thredded elbows and glue a peace of pvc in the non threded end then take the non thredded elbow and glue it to the other end of the same pvc at a 90 deg offset from the first
next we will take a second peace of pcv and glue it in the other end of the non thredded 90 deg elbow and finaly we will glue on of the 2 long sides of the t to that peace of pvc now this can be angled up a little if u like on this gun since it will not be used in a hand held configeration (at least mine isent since its only for testing perpouses)
to finish it up u will do the same thing for the other side only facing the same way so ur chambers are parallel if ur off by just a few deg. it will end up looking verry odd lol (it took me about an hr just getting it adjusted just right)
once y have it all adjusted and such u can twist on the chambers and head to the next step

Step 4: Barrel

all that relay physically needs to be done in this step is to attach the 1" * 2' pvc tube to the last open spot on the t

but this part is a part of my resurch and as such the length of the barrel is kinda hit and miss and one of the reasons i built this gun in the first place
i wos doing resurch and found out that there is a "magical ratio" that will allow u to get the most power out of ur gun
this ratio is called the c:b or chamber to barrel ratio apparently this ratio is from 0.5:1 - 1.2:1
to find this ratio u take the volume of the chamber and divide it by the volume of the barrel and that will give u the first number in the ratio ( the second number is always one)
so for this particular gun the numbers with a 2' * 1" barrel are as follows

dual 2" * 1' chambers (117.305 ci total)(50.652 ci per chamber plus 16 ci for the pluming)
1" * 2' barrel (18.852 ci)
c:b = 6.2:1
optimal c:b barrel length 7' 5" (70.383 ci)

so as u can see this barrel is no wears near the optimal length i have since doubled the length of the barrel and it has defiantly added a lot more power to the gun so i cant wate to finish extending the barrel to find out if this ratio does really work
i will extend the barrel all the way to 7' 5" and record the results with video then past to see if it will start to detract the power again after its past the optimal length

Step 5: Ignition

ok as for the iggnition its a little tricky the way i did it is kinda a fale safe so that if one chamber dosent spark off the other dosent eather that way ur not dealing with a half fired cannon.... (granted this all depends on if u dont use paint.... it dosent have a varry good ignitaablity so there fore dosent lend well to being to ritch or lean (ie. to much fuel or to little))

all i simply did for the ignition is took 4 wood screws and drilled them into the chambers so there is a small gap between them and there wos one gap per chamber

next u will take the 2 screws that are on opsate chambers and wire them together
the other screws will receve one wire from the igniter each so it makes a compleete crecte

if u do not get spark in the chambers try adjusting your gaps closer since this ignition sorce is a relitivly low power it will need small gaps i have since adjusted my gaps out to the max for better ignition

Step 6: Fueling and Launching

ok hopfly at this point u have compleeted the gun and let it cure for a minimum of 4 hr but make sure u lte it cure for about dubble the time spesified on ur pvc cemment

NOW AT THIS POINT I WILL GO A HEAD AND STATE THE OBVIOUS IM NOT A GUN SMITH

THIS POTATO CANNON MAY BE ILLEGAL IN SOME STATES IN THE US OTHER COUNTRIES IM SURE THERE ARE SOME LAWS AND SUCH ABOUT THEM AS WELL ALWAYS CHECK UR LOCAL LAWS AND REGULATIONS

THIS CANNON WORKS WITH EXPLOSAVE CHEMICALS AND LOTS OF PRESURE SO ALWAYS BE CAREFULL

PVC SHARDS CAN BE DEADLY AND HEART ALOT IF THEY GET INBBEDED IN U FROM UR POTATO CANNON FALING SO DO THE RIGHT THING AND BE CAREFULL IM NOT RESPONSABLE IF U DONT USE UR HEAD AND BLOW OFF SOME FINGERS OR SOMETHING BECAUSE U THOUGH U WERE A HOT SHOT AND INVINCABLE

that being sead i orrigonaly used white spray paint that wos hourroble i could onl get one chamber to fire at a time because if i added it to both sides the second chamber i filled would become over filled but if i only filled one chamber it never mixed correctly
to fix this i used old spice body spray it seems to have much better flamability and because of this it is more tolerent to how much fuel u use

this gun also has a relitivly small barrel size so all i have fired from it is grapes rapped in tolite paper.....

but to fill it u just spray a little body spray in each chamber close them with the close out caps slide ur ammo of choice and press the botton on the igniter and pow!!!!

have fun!!!
spcolsson (author) 4 years ago
ya i cant type for nothing next one i will have my wife go over as far as all that goes. Well honestly to answer u about the 2 chambers ive just never seen it!! I like the dual chamber because the chambers act like a stand for the gun that way i don't have to always hold it to fire it. i have increased the barrel length and it has helped out a lot so im going to stretch it once more. this build in particular had 2 reasons, 1 to find out if the dual chamber would even work, and 2 to see just how i would have to measure the barrel and chambers, ie does the pluming get calculated with the chambers or barrel. It turns out the pluming will need to be measured with the chambers.
From the innital tests the dual chamber seems to be more of a hastle without the propane meetering and such but the netx prototipe will clear that issue up.
The project as a hole has a few goels to meet
1. it must be capable of shooting a 3" dia object to about 200 meters
2. it must be as compact as posoble in its broken down stage
3. i must be able to fire it alone with no out side help, ie no one helping to hold it or a stand to hold it

so the project does seem to be on track the next build will actuly be a dual 3" * 1.5' chamber with metered propane and interchangeable barrels and maby (depending on funds available) a angle adjust for the barrel
this stage will be in 2 phases. first phase will be barrel interchangeability and the effectiveness of different but still mathematically correct barrels. the second will finally introduce me to metered propane and introduce metered propane to the project.
ilpug4 years ago
great idea, and great build, but i have several things to say:

1. you need to clear up the spelling and typing a bit. im not much of a grammar freak, but it does bother me when spelling gets in the way of telling me about an awesome project like this one.


2. why two chambers at all, why not one big chamber? it seems like all the extra plumbing is just extra space to be filled. keep in mind that the magical ratio states that there is a certain amount of barrel for a certain amount of chamber. this is an interesting concept, and i recommend you another cannon to test it's effectiveness. build a cannon with one large chamber equivalent to the two chambers you have now, and the proper barrel length according to the magic ratio. test this cannon and the double chamber one in identical conditions. which fires the best? i am honestly curious to know.

3. i reccomend a change in fuel. pretty much any kind of hair laquer or spray containing dimethyl ether is the ideal fuel for potato cannons.

4. safety rant: NEVER USE PVC. USE ABS. PVC SHATTERS (as you said) AND ABS TEARS. I KNOW ITS HARDER TO FIND EQUIVALENT PARTS IN ABS, BUT SAFETY IS WORTH IT!

all that being said, great project, and i hope to see more from you in the future.
DAE (ilpug)