BIKER180360 wrote:i plan on making a bunch of guns and i don't want to buy a whole bunch of bbq igniters?

Two words: alligator clips

I agree with the comments regarding no need for two different pressures. It does look like a design that has minimal pilot volume losses and a rapidly open valve. If you can manage the complexities of the multiple seals, it looks like a pretty potent spudchucker.

Good luck.

Why the hell should I define it as a polynomial function (I'm assuming you meant of the X^Y type) when a much simpler - and physical meaningful - formula exists?

<flame>
I said pick a polynomial of order that matches the model. If you have to go 4th or 5th order to get a good fit to the data, and ...

The form of the formula was predicted through a bit of applied physics (see description of pressure integrated over barrel length), and the constants found via trial-and-error minimalization of the chi square (or whatever it's called).

There are curve fitting programs that will let you fit a ...

... and get actual chrony data. I'm going to try and get one from my local paintball shop for the day but I'm not sure if they'll let me...

Here's a link to a chrony design that you should find easy to build. http://home.earthlink.net/~jimsluka/Jims_chrono.html It's basically two photodiodes ...

So what you're telling me is that your 40psi of quieter combustion is stronger than my 120psi of air? I look at it this way......... I've got no "whoosh after the "pop" like my last pneumatic did.

You've got it right. 120psi is storing a lot of energy and you're using almost all of it to ...

My pneumatic is very soft...almost silent...But I guess that's just me.

That implies you got the chamber:barrel ratios right. By the time the chamber has dumped it's air and pressure is back to atmospheric, the projectile is just clearing the barrel and there's not much "left-over" energy to ...

i like the bang of combustions soz but thats how i am

Nothing like a good loud bang to make you feel like you've got some lightning to match the thunder but that's not always the case. The physics works out very roughly:

1) Accelerating the projectile takes energy.

2) Making noise takes energy ...

Very nice piece of work.

I agree with the others that stainless steel is overkill for a standard combustion -- you're talking ~30psi to contain. That beast is screaming to become a hybrid. I say, "Cry havoc and let slip the dogs of war!" which is just a fancy way of saying, "Don't forget to post ...

I am not worthy. It's a truly awesome piece of garage engineering.

...
The circuits come as kits. One was an adjustable timer I modified to countdown from 4 secs. It activates the..

I'm interested in using electronic control of my guns as a route to learning some simple circuit design. Kits ...

Cleaner, more readable -- especially for long sessions when the low contrast blue/black would make my eyes bleed but overall a little less cool.

Still, I like it a lot for being far more functional. Keep it.

When your building a regular combustion spud gun, what raitio should you use between the area of the chamber and the barrel.

~JDSpud

Lighten up guys. He didn't ask how many people would like to tell me to go f*ck myself.

Here's some research
http://www.burntlatke.com/launch.html

Try this ...

...did salt and ice make dry ice or was it some other kind of reaction?

Salt had little or nothing to do with it -- it was simply sudden freezing.

Water ice is less dense than liquid water, i.e. it expands as it freezes. Dry ice quick-froze the water in the skin cells (probably several layers ...

medievalman wrote:...use a burst disk for a valve.

I thought of that. Any recommendations for disk material that would burst around 100psi? I searched the forum and the Wiki. Nothing in the Wiki, too much in the forum. is there a FAQ I'm missing.

I came across some mention of dry ice as a propellant. Looks like it could be fun but kind of tricky to work with -- pressure builds as the CO2 sublimates but how far and how fast? You have to mount gauge and watch it to make sure you don't over pressure the chamber.

I have a pneumatic with a gauge ...