My First Combustion (more or less)

[DirtyDan]

Greetings everyone!
The name's Dan... DirtyDan if you prefer. This is, as I am somewhat reluctant to say, my first post here in the forums. Seeing as how it's summer time once again and I'm currently jobless and waiting to start college life later next month I've elected to give my once-dead spudgun hobby another go...

I'd love to say that this was my first cannon, but sadly that isn't the case. My first was a rather crude and devastatingly simple, bare-bones combustion (you know, the kind you see the kids playing with on YouTube...). After some underwhelming performances with that gun I thought that perhaps spudding wasn't for me, but after some time spent perusing sites such as BurntLatke and of course the plethora of info provided by SpudFiles, I figured I'd burn up some graduation money and give it another go with my newly acquired knowledge and try to make my first moderately advanced combustion spudgun.

It turned out to be a very difficult yet rewarding experience to say the least. Trying to sift through all the information out there on C:B ratios, propane injection, chamber fans, and ignition sources and attempting to make sense of it all was needless to say a little intimidating, but within a couple of days (using some plans I found somewhere in these vast forums) I was somewhat complete with my new gun. I was however, extremely displeased with its performance. That is, until I installed my fan (which I had been dreading to put it, having never soldered a wire in my life). I'm happy to say it functions quite well; both my friends and I were amazed at how much performance such a small thing could provide.

So right now I get a pretty consistent 175 yards or so with an often ear-ringing noise that the neighbors don't much appreciate. I'm still unsure about the amount of propane I'm using (I use two metered shots of about 65psi with an 8" meter pipe and the chamber is a little over 5000mL if I remember correctly). I'm not really sure how much distance I should be expecting with this setup so I dunno whether or not I'm doing something wrong, so if any of you who bothered to read all this have any suggestions as to what I can do to increase performance with this rig I'd greatly appreciate it as I'm still pretty new to the whole spudgun world.

anyhow, here are some specs for the gun:

5000mL Chamber
2"x64" Barrel (a bit longer than the one pictured)
3/8"x8" meter pipe
80mm 12v PC fan (running 9v cuz im a noob at electronics)
BBQ igniter (only one spark gap)
and a very crudely attached green laser sight

EDIT: earlier I posted that my chamber was 1500mL... not sure why I typed that... my chamber is in fact approximately 5000mL... I know I know... pretty drastic typo.

[f.c]

thats nice what performance are you getting on it. and what ignition is that ?

[CpTn_lAw]

it's al in the text........please read before asking questions that don't need anwsers.....
Anyways, cool gun, nice design, fairly simple and yet effective; allied power and ease of use...congrats mate! I suggest you run a little math to know if your propane injection is sufficient or unsufficient. Ideal ratio is 4% propane for all the rest of air.
Nice cannon!

[iknowmy3tables]

thats a pretty large chammber, just larger than nessesary, but its really cool, but about your name we had an infamous dan before that was ban just to let you know

[mark.f]

Good job on the gun. I have to ask, though, about your fan placement. Is it all the way towards the front, (barrel end), of the chamber? And which way is it pointing? Not too important but I'm just curious.

Your meter settings make no sense to me. You should only need 41 PSIG of propane, (one shot), to achieve a 4.2% mixture of propane:air in a 1500 mL chamber with a 3/8"x8" meter pipe.

P.S. - good job on grammar, formatting, etc.

[iturnrocks]

I have to ask, though, about your fan placement. Is it all the way towards the front, (barrel end), of the chamber? And which way is it pointing? Not too important but I'm just curious.

Judging by the photos I would say the chamber fan is at the back of the chamber (note the location of the propane tap). I would say the photo was taken when the chamber was unscrewed. I cant quite tell from the photo which direction the fan is facing.

Im wondering if there is only 1 spark gap what are the other set of long bolts for?

[DirtyDan]

Well first of all, thanks for the positive feedback guys! I'll try out using 41 psi today and see if that's better, but I could have sworn that while using one of those fuel calculator things on BurntLatke that I needed a whole bunch more, but I suppose I'd take your word over mine on this subject... and in response to the whole fan thing, yes, the pictures were taken while the chamber was unscrewed. The fan is friction mounted rather tightly in the far back and blows forward toward the barrel (not sure if that's the right direction but it made sense to me). There is only one spark gap, but I used the same kind of long bolts for my fan electrodes and used quick connects... hope that helps clear things up, I know my pictures are a little misleading.

EDIT: ok I edited my initial post... for some reason I said it was 1500mL instead of 5000... I hope the amount of propane I've been using seems a little more reasonable to you guys now...

[iturnrocks]

I hate to admit it, but I used the same fuel calc and was coming up really high too. Eventually, I realized that I was using Diameter to calculate the volume of my cylinder rather than Radius like the conversion tool requested. For that reason my first spudgun has a 12" 3/8" meter pipe. Aside from being rather bulky its ok, I just use lower PSI now. Now if I could just solve my spark problem. I guess its the zinc plated bolts. Im installing stainless bolts today.

[sgort87]

For this chamber, you should actually need to run this meter at about 170 PSI. Even your 2 shots at 65 are low. Try doing 2 shots of 85 PSI.

You can make the process of metering easier by using a 10" long 1/2" pipe and running that around 80-85 PSI. You'd only need to meter in once each shot.

[DirtyDan]

thanks a bunch sgort... I'll surely give that a try once I'm done painting my gun... (already have it all masked off and taken apart) I was thinking about going with black and burgundy cuz I have a really nice guitar strap of the same color scheme that I was gonna rig up on my gun to make it easier to hold and shot since it weighs a ton...

[sk8er548]

i have a question I am about to build my first spud gun with a propane meter in a few weeks and i want to know whats the fitting called that connects the meter to your spud gun. because on the gun i make i want that kind of fitting.

[SpudBlaster15]

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[sgort87]

This is true. But the pressure I gave there (170) was for the meter he has on it now, which is a 3/8" pipe, not 1/2". I told him to up his pipe diameter and extend it.

Someone needs to work on their Reading Comprehension.

[SpudBlaster15]

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[sgort87]

Well, I guess you're right. I thought last time I checked, that I got a caliper reading of .40, but it must have been obstructed by the lip of the pipe, or maybe I'm an idiot. I suppose that's what I get for not checking Fuel Tool. (I would have, but I was at work and couldn't access it.)

Latke's measurement is .47", but it varies from brand to brand. And when we take into account extra volume in the ball valves, temperature differences, and ambient air pressure changes, we get something in the neighborhood of 120-125 PSI.

You win this time SpudBlaster15, but I'll get you eventually! Muahahahah!
*runs off, cape flowing in the wind*