SpudFiles

Hey everyone. Last summer I made a horribly disproportional combustion gun that I just used Axe in (got it to fire off unmetered propane once.. what an increase in performance) Here is the one I made:



If I did the calculations right, it has a 1:2.562 C/B ratio lol. Well.. I decided that now instead of going to Home Depot and winging it on the calculations, I wanted to make a decent metered cannon but I had a few questions.

1) I read that PVC is acceptable because propane only creates 90psi at most and the correctly rated PVC pipe can handle this. Fact?

2) On a meter, whats the point of the pressure gauge? If you open one valve to let propane in and close it, then open the other to let it in the chamber, why would PSI even matter? I understand that higher pressure would require a shorter meter pipe, but what is the average pressure of a 14oz propane tank so one can find a suitable pipe length for the appropriate pressure and chamber size?

3) What is typically a good chamber and barrel size? I know the volume ratio is like 1.5:1 but in terms of inches and diameter of PVC, what is the norm?

4) Is a straight through design better or is a chamber on the bottom looping up to the barrel good too.


I tried looking for the answers to these but I came up empty handed so hopefully someone can enlighten me. If I remember anything else in question I'll bring it here =) Thanks.

i would say for the very very normal combustion.

diameter wise, a 3" chamber and a 1.5" barrel

welcome to spudfiles!
1) yep it will work just don't get celll core
2) for best results use 4.2% propane. since this is hard to measure in the chamber you use the meter since it is smaller it will reach a higher pressure that you can measure
3)sthorne already answered this
4) either one is good an over under would be more compact and easier to hold.

Go to burntlatke and use ratcalc to calculate your ratio.

thanks, number 2 is a little confusing the way i put it. if you can explain it a little better it might help him more.

you will use a gauge on the meter pipe to find the right amount of pressure in the meter to make it 4.2% in the chamber.

How do you change the pressure in the meter though? Say you're aiming for 4.2% but your pressure is too high, do you just open the first valve less to let less propane pressure in and quickly seal it off?

Ecstasy wrote:How do you change the pressure in the meter though? Say you're aiming for 4.2% but your pressure is too high, do you just open the first valve less to let less propane pressure in and quickly seal it off?

Get yourself a regulator and put right after the open valve on the propane tank. This will let you control the pressure heading into the meter. You'll need to control the pressure based on how large your meter is vs the amount required to make 4.2% of you chamber.

Something like this http://www.lowes.com/lowes/lkn?action=p ... lpage=none works fine.

As elitesniper suggested go to Latke's site www.burntlatke.com and read up on metering. It may take a couple of times though it but he does a good job explaining things.

i just re designed the meter on my gun and the regulator i had is sh!tty at best so i just open the first valve slowly and watch my gauge to get it up to 50 psi which on my meter is 4.2% but using the gauge i can dial it down a little bit if i wanna lob a shot instead of blasting it out of sight

Oh nice, thanks for the regulator link. Just need to figure out how that would be threaded

So I've been thinking of ideas for power for an exhaust fan, mixing fan, and ignition system and rather than pounding through 9V batteries, I remembered that I have this 12V rechargeable battery from when I raced RC cars (used for starting the engine). Think it would be a good solution to somehow mount it to the cannon and attach all the wires and switches to it? I don't really care about weight. It's 12V 4.5Ah.

I'm sure I can run a 12V 40mm cpu fan off of it with like a PVC ball valve attached to the end cap of the chamber, but think I can make a spark strip with it..?

Edit: this is the battery
http://www3.towerhobbies.com/cgi-bin/wt ... LXSK06&P=7

Too bad he doesn't know if I should use a 12V battery or not =(

Ecstasy wrote:So I've been thinking of ideas for power for an exhaust fan, mixing fan, and ignition system and rather than pounding through 9V batteries, I remembered that I have this 12V rechargeable battery from when I raced RC cars (used for starting the engine). Think it would be a good solution to somehow mount it to the cannon and attach all the wires and switches to it? I don't really care about weight. It's 12V 4.5Ah.

I'm sure I can run a 12V 40mm cpu fan off of it with like a PVC ball valve attached to the end cap of the chamber, but think I can make a spark strip with it..?

Edit: this is the battery
http://www3.towerhobbies.com/cgi-bin/wt ... LXSK06&P=7

12 volt battery should be fine. can you send a pic, im not quite sure what a 12v looks like. and are you planning on powering the fan and a stun gun with it?

EDIT: nm on the pic, didn't see the link you posted

sthorne i am up for the fight
i just need to trace some IP adresses

spudfarm wrote:sthorne i am up for the fight
i just need to trace some IP adresses

??