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Short question topic

A place to ask general spud cannon related questions.
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Re: Short question topic

Unread postAuthor: hectmarr » Sun Jul 22, 2018 12:20 pm

You can look at this, maybe you'll find something, in case you have not seen it.
It seems to always be something bigger than the head so that it fits in the grooves.
https://airenlaces.blogspot.com/2012/10 ... bolos.html
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Re: Short question topic

Unread postAuthor: farcticox1 » Sun Jul 22, 2018 12:43 pm

That looks good thanks, was looking at this tubing for a smooth bore, it is 4.572mm ID so could work with the right pellets.

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Re: Short question topic

Unread postAuthor: hectmarr » Sun Jul 22, 2018 12:59 pm

Maybe it works. You must do the test to see how a 4.5 pellet fits. How do you plan to make helical grooves?
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Re: Short question topic

Unread postAuthor: farcticox1 » Sun Jul 22, 2018 1:09 pm

No rifleing, just smooth bore.
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Re: Short question topic

Unread postAuthor: hectmarr » Sun Jul 22, 2018 1:50 pm

I have tried this type of ammunition in smooth bore but I have not managed to get it straight. Hit the target with any part. My ammunition was 5.5 mm, but I do not think it influences very much. The truth, if the precision you need is not very important, I do not think it's a problem.
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Re: Short question topic

Unread postAuthor: hectmarr » Mon Jul 23, 2018 10:14 am

mrfoo wrote:
Has anyone tried it? works?

Yep, it works as a dirty hack, but you'll only get low pressure from it. The absolute maximum pressure you can theoretically achieve will be ambient atmospheric x motor compression ratio once the ports are closed. Generally, for a 2 stroke model engine that's gonna be around 7:1 max, so you'll maybe get something approaching 7 bar "stock", perhaps more if you resleeve to eliminate the exhaust port and work hard to minimise dead volume in the cylinder.

If you're machining, why not machine something better...

We measure with a compressometer for these small engines, those that are screwed in the spark plug, and are about 9 bar. It is an automotive racing engine that is working perfectly. I imagine that the pressure that can withstand without great losses is greater than 9 bar, because when the air-fuel mixture ignites, the pressure peak should be several times higher. If the piston would let this explosion pressure escape, the small engine would not work. If it behaved like a combustion chamber of a 9X hybrid weapon, the pressures it could handle would be around 8 times more .... I have to do tests.
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Re: Short question topic

Unread postAuthor: KnooBill » Tue Jul 24, 2018 1:12 pm

Hello, after playing a bit with my primitive QEV & slide valve rifle I wanted to build something nicer. I browsed a bit for ideas, read about those nice trigger 3 way 2 position valves, ordered one, it arrived. Inspiration has been this project: pneumatic-cannons/topic26765.html

First of all, one hole is off centre, spoke with the seller and he says it is actually so, and in another listing which had pictures of the holes it was actually off centre as a new design. I guess this will be the port completely open to the atmosphere. Second picture here, mentioned in another thread, bought the same one:

https://www.ebay.com.au/itm/Mechanical- ... 2138858584?
epid=1255627187&hash=item2814468858:g:J6MAAOSwCGVX9I-X

Currently by my super scientific method of blowing into it, I can tell that A and R communicate while P is closed, when the trigger is pressed P communicates with A. As I don't want to drill small holes into my QEV, should the connection be QEV P (pilot?) port --- JM-07 P (pilot) port?
Then A port on the QEV will be the secondary chamber housing shot air, while the primary chamber and filling port will be between the P ports of the QEV and JM-07, while the A port is plugged off by an adjustable chamber (as seen in a video here: pneumatic-cannons/topic26793.html , though he has perforated his QEV) to find which volume suits me best?

Plenty of questions actually :D
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Re: Short question topic

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Re: Short question topic

Unread postAuthor: farcticox1 » Tue Jul 24, 2018 5:35 pm

If you don't modify the QEV I think this should work.
Now I realise the sealed exhaust wouldn't work as it doesn't vent to atmosphere after firing. :shock:
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Re: Short question topic

Unread postAuthor: farcticox1 » Wed Jul 25, 2018 6:03 pm

That's a good layout for a single shot as it will dump the whole chamber , that's how I did mine.
001.jpg

SS (1).jpg

SS (3).jpg
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Re: Short question topic

Unread postAuthor: KnooBill » Wed Jul 25, 2018 8:29 pm

Thank you but you got me even more confused :D Perhaps I have grasped the concept of your second post below, ditching the adjustable exhaust volume, which I don't comprehend anyway, as I cannot explain power and exhaust volume correlation, ie low volume - more power

From what I understand I got a normally closed valve, so making this pneumatic-cannons/topic26765.html is viable or do I have to keep the trigger pressed and it works when released? Will be trying fitting my JM 07 https://www.ebay.com/itm/JM-07-1-4BSP-T ... Desc=0%7C0

JM-07 R port to QEV P, JM-07 P port to air chamber, looking at regulated paintball tanks which I call fill witha pcp pump as it had been suggested. Of course QEV A port is the shot chamber. In the earlier post I am probably wrong to connect QEV P to JM-07 P as the air chamber won't be shut off. Considering that the total cost will exceed hobby money(over 140$) I want to get everything right before ordering the expensive parts.

Would I by getting this https://www.ebay.ca/itm/Air-Pneumatic-2 ... 100623.m-1
connecting QEV to A, air chamber to R and P left to the atmosphere, I would be able to have multiple shot without any QEV perforation?

EDIT it seems that my inspirated was in turn inspired by these posts spud-cannon-related/topic13147-2115.html?hilit=roller
I've got to get the 2 position 3 way valve function down.
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Re: Short question topic

Unread postAuthor: farcticox1 » Thu Jul 26, 2018 4:27 am

The adjustable exhaust will give you adjustable power for each shot, without it the whole chamber will pretty much empty each time. But only if you fill through A and modify the QEV if your using a 3/2 trigger, which I believe you already have.

What do you want to build exactly ? What parts do you already have and want to use ? do a drawing and maybe start a seperate post :idea:
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Sat Jul 28, 2018 6:47 pm

KnooBill wrote:Currently by my super scientific method of blowing into it


Hey, it works ;)

I can tell that A and R communicate while P is closed, when the trigger is pressed P communicates with A. As I don't want to drill small holes into my QEV, should the connection be QEV P (pilot?) port --- JM-07 P (pilot) port?


If A is the common port, then it should be attached to the QEV pilot port.

If A communicates with R when the valve is at rest, then R should connect to your main chamber, while P should be left open.

an adjustable chambeto find which volume suits me best?


Easier to use GGDT to determine what size of chamber will give you the performance you're after.
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Re: Short question topic

Unread postAuthor: hectmarr » Fri Aug 03, 2018 11:52 am

Does anyone know what this red knob is for?
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Fri Aug 03, 2018 12:06 pm

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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: Short question topic

Unread postAuthor: hectmarr » Fri Aug 03, 2018 2:12 pm

:) Solved!
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