Butane badness

Step 9 Wrapup

Notes on Ammo

Marshmallows
These work great. Chaptstik tube uses them native from the bag...minimarshmallows. I like to dry them out though till they are good and crusty. I carefully roll them to near barrel diameter and use the barrel like a mandrel to "extrude" them. This sets a perfect diameter and works great.

Tic-tacs
Already discussed, work great, become sticky with time...water is a product of combustion. sticky is not good. They're cheap, buy more.

Straws
You would be amazed at the performance of a short length of soda straw with wax vs hotmelt glue plugging the end. Add a sewing pin and you have nice darts.

Wax balls, Hot melt glue tubes, foam plugs, balls of yarn, peas, beans, spit-wads...have a blast. The range is from harmless short range stuff to fairly lethal. The marshmallow can seem nearly lethal with a long barrel. So many possibilities....have fun.

The Future
I like breechloading better than muzzle loading.

I like having the gasflow control seperate from the spark control.

When the projectile fails to leave the barrel---it becomes a film canister cannon. The pressure builds till the canister seperates from the lid. This is LOUD = ouch my ears, especially indoors. Can this be fixed while still having a pressure release mechanism for safety?

I would like some muzzle velocity measurements. I am exploring high-speed photography among other things for this and I would like some nice pictures.

Basically, this is the beginning, stay tuned for more.

Feel free to offer suggestions / improvements / post your own designs.

Comments

[Quw10]

Wanna make this more interesting you should make a crude blow back loading system so it atleast reloads by gravity, you know like opening a trap door or something but probably will be tricky

[jupeter5]

Wow this is really cool i must build one, keep up the good work

[krugerm]

I have a quick question do you have to open the chamber every time you reload because of lack of oxygen, or have you found a way around it? I ask because i have some mini spud guns and they can have enough fuel, but i run out of oxygen to do multiple shots without reopening the chamber.

[corpse--paint]

s = v sin a t - 1/2g t ²

v = (s + (1/2g t^{2))/ sin a t}

g = gravity (9.81)
s = distance
t = time, meaning you could use the time code of a video etc
a = angle of launch

make sure you launch from ground level though, or the equation doesnt work

[firefighter1333]

btw how do u calculate/measure the fps of any gun?

[firefighter1333]

corpse where is this for exactely (im just curious), could u explain this to me? pls? (im such kind of person who likes fysics and stuff but who not always understands)

[fd93]

for the pressure problem try drilling a small hole in the chamber and plug it with some hot melt glue them if it fails to fire punch the glue in and the pressure will release through the hole rather than turning the canister into a pressure vessel

[cliche_cliche]

I've just completed mine! But I did a few things differently, mainly because I didn't have the parts you descried in the materials needed.

Here's an image of what mine looks like: http://img412.imageshack.us/img412/2055/p1011352qz5.jpg

I used a wooden stake for the wood, a medicine bottle (though not very interchangeable), and a 6mm airsoft barrel with bbs.

One minor, but less complicating change I made to your design was the connection to the piezo element. I left the pen spring out and used solid core wire, which is easy to wrap around and won't come off. It also made the bridge for the spark easier to do.

I am more than impressed and pleased with this nifty little device.

Though it is fun, it's not exactly consistent in both firing first try and fps, thought it was made for under 10 bucks, so there's not much consistency to expect!

Do you have any techniques for firing and FPS consistency?

Thank you for the instructable!

[bench.worker]

You ask a great question...and thanks for the pic! I've found that the following points are key: 1. reliable spark - sometimes these piezos fail, or there is arcing between the wires in places not intended... 2. reliable fuel-air mixture. This is important for both consistent power and consistent triggering. I'm working the second problem. I have a nice prototype and am working on a field-deployable design that is a bit simpler to construct. Stay tuned.

[the gizmoman]

try shooting cotten balls soked in alcahal or other flamable liquids

[YummyPancakes]

Fireballs! Hehe. Ha ha ha. MWAHAHAHAHAHAHA! AHAHAHAHAHA! MAHAHAHAHA! Sorry you had to see the evil genius in me...

[manmelvin]

Oooooh flaming projectiles i like o__0

[ilpug]

that is a really good idea. dangerous, but good.

[Kiteman]

I would like some muzzle velocity measurements. I am exploring high-speed photography for this and other interesting image capture.

Try a ballistic pendulum instead:

http://webphysics.davidson.edu/physlet_resources/bu_semester1/c12_ballistic.html

[killerjackalope]

how bout a defined shutter time and a scale in the background like 100/S shutter and a metre rule as close to projectile... take start of the blur to the end of the blur on the ruler to find out the distance travelled in 100/S x 100 gives you cm/s and leaving it undivided gives you M/s

[Kiteman]

Or video at a known frame-rate (say 30fps) and compare adjacent frames?

[bench.worker]

Alright, I have been experimenting with an ~30 fps video camera. I have collected quite a bit of data but have not completed the analysis. What I have found so far using a marshmallow as the projectile: 1. It is difficult to see in flight against a well lit dark background 2. It can travel 2m in a single frame 3. Frame rate is constant but exposure or "on" time varies with ambient light 4. This means "off" time varies as well 5. one must determine the "on" to "off" ratio for accurate calculations 6. it would be nice to have a "slow" constant velocity object to calibrate this Roughly, I can estimate that we're seeing 91 m/s or ~300 f/s. Stay tuned, detailed analysis to follow along with better performance pics...video?

[Kiteman]

1, 2. Try a banded background - black and white stripes of known width (1cm?) to allow accurate measurement of distances, plus increasing the chance of spotting the 'mallow.

At 30fps, 2m in a frame = 60m/s, not 91m/s.

60m/s = 134mph = nearly 200f/s (not 300, but still impressive).

3, 4, 5, 6:

Make or buy a clock with a smoothly-moving sweep-hand (as used by crash-test centres) or a simple "bob" pendulum of known length (and hence calculable period).

[bench.worker]

The banded background sounds interesting I'll have to try that. As it is, I've included a measuring tape in the video which I then use to calibrate the image processing software. As for velocity calculations: At 30fps you would be correct if each frame was exposed for that entire time. I was interested to discover that this is not usually the case. Time is necessary to record each frame. Beyond that ambient light can change dramatically--this is dealt with by varying the exposure time of each collected frame. The maximum exposure time would be 1/30th of a second, but under bright lighting conditions this could be significantly less. The meaning of all this is that the data collection rate is 30fps but the actual exposure time of each frame will be somewhat less than that. I'm estimating that this could 50-60% with the setup I'm using. Hence the time scale of the recorded distance per frame is less than 1/30th of a seocnd. I do like the pendulum idea. The need for a known velocity is not so great as the need for a fixed velocity. This will allow easy calculation of the exposure time of each frame as a ratio of the collection rate of 30fps.

[killerjackalope]

yeah I used the 100/S as a way of getting a direct measurement, timing would be everything and prefocusing is a must but the video idea might provide more reliable figures say: (travel over 10 frames)/30 = velocity in M/s also using ten frames cuts down on error by a huge amount.

[bench.worker]

These are good ideas. Thanks for your patience with this. I have been spending time elsewhere of late, but I am interested in collecting this data. I will try out these suggestions - there are a lot of potential pitfalls, but planning to avoid them will take time. I may get lucky just by trying.

[killerjackalope]

yeah a decent camera with a reliable framerate or shutter timing is the main thing to get over then timing the firing and capture so video is a better bet

[bench.worker]

This is an interesting idea that I also had in the back of my mind. It may acutally be simpler than I imagined it. Thanks, I'll check it out.

[ilpug]

Another way to find speed is to make and cast some ballistics gel (i think there is an Instructable for this), and fore into it at point blank range. Then, i think, by using some fancy math that im sure you can find somewhere, you should be able to find out how fast its going.

[hamishofangus]

Muzzle velocity figures are very easy to calculate with simple projectile motion formulas based on the principles of Newtonian physics. If you can measure:

Angle of inclination at launch
Flight time
Distance of Flight
Vertical Acceleration (roughly 9.8m/s^{2 most places on Earth)}

You can solve for the velocity at the time of launch. Simple and accurate. Can't remember the formulas right now, let me look it up and get back to you.

[gamma_fear]

one problem, wind resistance will through off your calculations.

[bench.worker]

This is assuming of course no friction. In this case we have relatively light projectiles of low density traveling through air. Marshmallow is larger than a cubic centimeter and weighs what, a gram? Volume-wise I think it is mostly air. I believe the error induced by assuming no friction would be substantial. It would underestimate the real velocity--this may in fact be useful, defining a lower limit on performance. There are other more suitable projectiles--still there is another issue. The data necessary to do this calculation do look simple on paper but to actually collect these in with any accuracy is challenging. These are the two main sources of error i see in the calculations and are why I have not pursued this method.

[manmelvin]

Wow i tried to make somthing like this but it doesnt have an kind of chamber so it didnt work.