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My cannon, revisited.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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My cannon, revisited.

Unread postAuthor: McFear » Mon Jul 28, 2008 7:58 am

hey all

as some might possibly remember, a few months ago i posted up saying about my cannons, http://www.spudfiles.com/forums/my-gun-t12999.html

Image

for all of those that havent looked through the old thread, the chambers are 100mm diameter and 400mm long. they come into a T joint that the chamber follows from which is 65mm diameter to allow a tennis ball to fit perfectly and is 2m long.

ignition was a bbq piezo electric ignitor, but it died after a month of use, so for now im just using a lighter against the side of the chamber, (yes one chamber). in future i am going to be running a camera flash ignition through both chambers at once so that should make it run a bit more efficiently.

the fastest shot i got out of the barrel was 182.71 m/s. this was gotten from using a motion sensor that i borrowed off my school. it was using a refresh rate of 250hz.

the range on the sensor though was only 1 meter so there is some inaccuracy for total speed because it was only measuring the muzzle velocity of the ball. i had the sensor set back about 1.5m so that the initial burst of gasses wouldnt be recorded and that the speeds recorded were actually the tennis ball.

here is a video of it shooting a tennis ball through 1/2inch wood and then through a towel which i stupidly thought would catch it.
[youtube]http://www.youtube.com/watch?v=quF4PRC6USw[/youtube]
and here is a video of it shooting a tennis ball at 5 degrees to the horizontal into a headwind, 180m.
[youtube]http://www.youtube.com/watch?v=XCTBgzcQZ9Q[/youtube]

i think thats all for now. i just thought that some people would like to see how my cannons are going. according to wikipedia, at sea level the sound of speed is 340.3 m/s.
my cannon is reaching just over half the speed of sound.

i am fairly proud of that. with all the chrony data, i was only firing off one chamber, the other chamber was fueled, but wasnt igniting until the flame front of the initial chamber reached the intersection. this would prob lead to a longer lasting flame front, but when the projectile is moving that fast, i dont think that it would help that much. will try get this dual chamber ignition working in the next week or so and will see what that does for it.


ciao,


Ross
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Unread postAuthor: starman » Mon Jul 28, 2008 9:56 am

I would say that second chamber may have more effect than you think, especially with a tight fitting tennis ball. Just keeps providing burn time as the ball travels the barrel.

A burst disk could almost completely null out your flame-front-in-a horseshoe issue there and offer up some more % points in performance.

It does have some wallop to it. Are you sure you want to continue with the match hole ignition.
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Unread postAuthor: McFear » Sat Aug 02, 2008 2:14 am

can you please explain how i would put a burst disk in it. im not sure how it would go into it.

do you think that if i ignite both barrels at the same time, it will get some more power behind it?


re the ignition, i am changing it to an electric ignition soon. not exactly sure when, but i am making plans on how to best go about it.

Fear
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Unread postAuthor: starman » Sat Aug 02, 2008 2:23 am

McFear wrote:can you please explain how i would put a burst disk in it. im not sure how it would go into it.

do you think that if i ignite both barrels at the same time, it will get some more power behind it?


I burst disk with a cam coupler set and multiple (3 for 65 psi on a 2" adapter) layers of 2" masking tape like this:
Image

Others use multiple layers of aluminum foil and a pvc union for 1x combustions and metal unions on hybrid guns. Take a stroll through the hybrid showcaseand see generally how it's done.

In your configuration, I wouldn't bother with another spark in the other chamber... just move on to next design.
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Unread postAuthor: McFear » Sat Aug 02, 2008 5:10 am

so would i put that just before the barrel. at the union of the two chambers.
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Unread postAuthor: McFear » Tue Aug 05, 2008 11:31 pm

anyone else have anythoughts?
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Unread postAuthor: starman » Tue Aug 05, 2008 11:37 pm

McFear wrote:so would i put that just before the barrel. at the union of the two chambers.


This is how I implemented it with a golfball barrel...

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