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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: jackssmirkingrevenge » Sat Mar 22, 2014 4:54 am

cammyd32 wrote:Also from what I recall those valves aren't exactly brilliant hammer valves. The valve stem and seals on CO2 bottles aren't built for that kind of abuse, you could find yourself with a potentially very dangerous valve failure if you went a bit too aggressive with your hammer.


That and the flow isn't too great either.
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Re: Short question topic

Unread postAuthor: FuzzCake » Mon May 05, 2014 10:29 pm

First off, apologies for my first post here being asking a question and not a contribution. Not something I favor.

However, I'm at a loss here for something that may be simple; This video;


It may be a simple set-up, maybe not. I just can't wrap my head around how he's pulling that automated launch off. The chosen projectiles don't appear to be going much more than their own length down the barrel either.

EDIT; Thanks for fixing the video.

Anyway to further add to this now that I can: It appears to be an electric solenoid valve of some kind but...outside of that I got nothing. A trigger activation and such.
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Last edited by FuzzCake on Tue May 06, 2014 5:21 pm, edited 2 times in total.

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Re: Short question topic

Unread postAuthor: jrrdw » Tue May 06, 2014 5:20 pm

In the video description there is a link to a facebook page. Without going there I'm thinking the mortars are pre-charged/pressurized and use either a burst disk or a valve that opens when it comes in contact with a pin in the bottom of the launch tube.
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Re: Short question topic

Unread postAuthor: bravootome » Tue May 06, 2014 11:12 pm

he could use a optic sensor to open a solenoid sprinkler " valve..............my opinion
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Wed May 07, 2014 5:15 am

Doesn't even need to be as sophisticated at that, it could just be a simple contact switch.
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Re: Short question topic

Unread postAuthor: wyz2285 » Fri May 09, 2014 1:28 pm

So I was going to test casting some R-hop patches using silicon glue but when I opened the mold after 24h (more than enough time) it did not cure at all. Then I thought it must be in contact with air in order to cure and the mold was completely closed (obviously).
I know there are silicon mixes that uses a hardener like epoxy that can be used for casting, anyone can show me one? Preferentially something available on Ebay.
Thanks.
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Re: Short question topic

Unread postAuthor: jackssmirkingrevenge » Fri May 09, 2014 2:07 pm

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Re: Short question topic

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Re: Short question topic

Unread postAuthor: wyz2285 » Fri May 09, 2014 2:13 pm

Well now I'm confused. I found similar stuff on ebay, rtv silicon rubber. Is it used to make the mold or used inside a mold to cast final product?? From what I understood it's to make the mold. Then is it soft enough to be rubbery like o-rings/rubber washers?
Which category should I look into? Looks like they sell about the same thing like what I found on Ebay...
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Re: Short question topic

Unread postAuthor: MrCrowley » Sat Jun 21, 2014 9:07 pm

Just a question about my ignition circuit.

The main thing about the circuit is that it uses this sparker for ignition:
http://www.testntools.co.nz/sinsui-elec ... 30598.html

When I test the spark jumping under pressure, I can't here the spark jump inside the chamber as you often can with a stungun circuit but that's not surprising since this sparker dooes seem a fair bit weaker, especially when it jumps the small sparkplug gap. However, holding one of the wires slightly off the chamber produces a tiny spark jumping between the wire and chamber. This must mean that the spark is also jumping the spark plug so as to complete the circuit.

The weird thing is that the spark will jump between the wire and chamber even after I've stopped pressing the ignition button. It's like it has built up charge that it can't release in one go. On top of that, if I leave it to spark a bit after I've stopped pressing the button, and then touch the wire from the chamber to the wire on the spark plug, it produces a noticeable spark.

Anyone know what's going on here? Was wondering if it has something to do with the sparkplug I'm using. Hopefully it doesn't interfere with the ignition on the cannon but it'll be awhile before I can test whether this circuit has got the guts to work at 10x.
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Re: Short question topic

Unread postAuthor: jrrdw » Sun Jun 22, 2014 6:14 am

sales page wrote:WARNING - RESIDUAL VOLTAGE
When the unit is stwitch off there can still be voltage on the output. To discharge it short out the output terminals then they will be safe to touch.


Poorly built circuit? I like CDI breaker point set ups myself (for launchers). :bigsmurf:
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Re: Short question topic

Unread postAuthor: MrCrowley » Sun Jun 22, 2014 7:09 am

Yeah that is something I've noticed when testing the circuit off the chamber. But I thought that since one wire is shorting to the chamber, and the other attached to the spark plug, residual voltage would be dumped through that. Can't think of why it wouldn't dump until the chamber wire is held next to the spark plug wire.

Maybe there's something in my spark plug responsible, it's brand new and the guy wanted to know every little specification I required. I just wanted a simple spark plug but he wanted to know type of core I wanted and whether it should have a resistor (?) or not. I'll get the model number tomorrow and post it, see if that helps.
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Re: Short question topic

Unread postAuthor: jrrdw » Sun Jun 22, 2014 3:46 pm

Use a Champion LM J19. It's the most basic spark plug made that I know of. But, if the plug you have now fires between the electrodes it's working. Open the gap to .060 to simulate operating conditions, if it will jump that it will fire in your chamber.
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Re: Short question topic

Unread postAuthor: wyz2285 » Mon Jun 23, 2014 5:14 am

So I'm ready to machine the receiver and I was checking out the barrel.
Seems too long (60cm) so I want to cut it into 2 piece of 40 cm and 20 cm and left the 20 cm for perhaps a PCP pistol later on.
I know the finish on the exit side is very important, so what should I do? face it square and chamfer it slightly? At least that's what the stock barrel looks like
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Re: Short question topic

Unread postAuthor: jrrdw » Mon Jun 23, 2014 5:37 am

face it square and chamfer it slightly?


In a word...Yup!

The chamfer eliminates edge grabbing the ammo causing tumble, at least that's my thinking on why that's done. There very well could be a different reason for that, IDK for sure. :bigsmurf:
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Re: Short question topic

Unread postAuthor: MrCrowley » Tue Jun 24, 2014 2:01 am

So did some testing at 10x with my burst disk hybrid and the new ignition circuit. The spark was jumping the spark plug (different one to the tests from above) as evident by visible sparks between the chamber and wire. However, no ignition. One click of the piezo sparker, boom.

Is it possible that the spark has enough juice to jump the gap at 10x mixes but not enough juice to ignite the fuel mixture?
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