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Sparkstrip designs. ?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Sparkstrip designs. ?

Unread postAuthor: ozoncqp » Sun Apr 05, 2009 1:58 pm

I got a question about powerstrip designs.
I can't get threaded endcaps unless I want to pay 55$+ for one. And I don't want to glue up my cannon 100% if a thing inside should break, I'd hate to hacksaw my way though it.
So after browsing the forums i came by this. I forgot the original designer as the webpage died a few min after i found it.
Image
Im thinking of adding an O-ring between the pipe and the fitting by cutting a gap on a Lathe making it air tight.
But about my sparkstrip.
I made this prototype just to see if the idea would be useful.
Image
Image
Image
Ok so its just a standard sparkstrip but made into a spiral. apply 1-x gaps. Im planning 3-4, it should in my theory give a wider variety of flamefronts. Right?
Anyway, its designed like this as I'd like to bolt it together with my endcap, but to avoid having bolts all around the chamber, I made it into a spiral so both + and - is mounted in the endcap.
Its the same diameter pipe as the chamber itself, and it should be able to sleeve down the chamber with and avgr fit.

I also had another theory in mind, just making the sparkstrip into a ring, and apply the ring to the endcap just infront of the fan. But would that just make 3-4 sparks ignite the gasses into one big fireball, or would it still receive multiple flamefronts?

The spiral would give the flexibility of a straight strip but also place the flame fronts around the chamber.
And is there an optional distance between each gap?
Take a 4x20 chamber, would a strip of 20" with 5" between each actual gap be better than.
4x20 a 5" strip with 1" between each gap ?
These numbers are just theoretical.

Did this make any sense at all lol ?
/michael
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Unread postAuthor: jonnyboy » Sun Apr 05, 2009 2:20 pm

It would work fine but you would need two of them because it would just short at the bolt if you used it for both positive and negative. Just forget the o rings and epoxy it sealed.

More gaps is better because your fuel will burn faster and more simultaneously. Because the pressure lasts just a short time you want it to burn at the same time so you get more pressure. Your spark strip should be linear and should travel down your chamber.

Take a look at starman's triple thunder, he's got some excellent ideas.
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Unread postAuthor: Biopyro » Sun Apr 05, 2009 2:31 pm

Keep the o-rings! there's no point permanently fixing it if you don't need to.
To find out how many sparks you need, use this.

Length of chamber/diameter.

Ideally you'll want to place them in the centre of the chamber, evenly spaced. Having more gaps may increase the results but it's a point of diminishing returns.
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Unread postAuthor: jonnyboy » Sun Apr 05, 2009 2:59 pm

Well imo I would seal the fucker up. Nothing like a improper seal giving you a blast of very hot air. Burns aren't too nice. :wink:

Also why would you need to open it up? If you do unscrewing a bolt won't help.
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Unread postAuthor: Biopyro » Sun Apr 05, 2009 3:19 pm

Need to open it or otherwise, it's just better to have servicable components.
ozoncqp does specifically say he wants it serviceable.
Having said that, I did think we were talking about gluing in the nuts.
A combustion really isn't going to leak that much, I think blu-tac would be sufficient to seal it.
If, you've ever been "burnt" by an un barreled combustion or similar, you'll know that the burns they give are nothing. It scorches the top layer of skin if you do it repeatedly, you don;t feel it and it doesn;t blister.
I did it 5 or so times fiddling with a jam-jar pulse jet, and didn't notice until I saw my thumb looked a little scorched
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Unread postAuthor: ozoncqp » Sun Apr 05, 2009 3:47 pm

jonnyboy wrote:It would work fine but you would need two of them because it would just short at the bolt if you used it for both positive and negative. Just forget the o rings and epoxy it sealed.

More gaps is better because your fuel will burn faster and more simultaneously. Because the pressure lasts just a short time you want it to burn at the same time so you get more pressure. Your spark strip should be linear and should travel down your chamber.

Take a look at starman's triple thunder, he's got some excellent ideas.



Well I just stuck some wire on it to simulate a sprakstrip. Ofcause there will be made gaps in it.
And gueing it all up is exactly what i want to prevent. I dont want to hacksaw a cannon if the strip somehow fails, if the fan dies etc.

This blue tac, is that what I call liquid gasket ? I got something that can withsatin 500 celcius, I did plan on filling the gap before I add the O-ring.

Biopyro wrote:Keep the o-rings! there's no point permanently fixing it if you don't need to.
To find out how many sparks you need, use this.

Length of chamber/diameter.

Neat, thanks.
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Unread postAuthor: starman » Sun Apr 05, 2009 5:01 pm

As biopro said, gaps on the center of your chamber will be somewhat more effective than gaps around the chamber walls...full spherical, simultaneous burns rather than semi-spherical.

Have you seen the spark strip for Trip Thunder...

Image
Image

It requires only a 2 bolt entrance and can have as many gaps as your spark source can handle...obviously 3 shown here. While I think this design can be improved upon, it's very effective and reasonably easy.
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Unread postAuthor: ozoncqp » Sun Apr 05, 2009 5:06 pm

Yeah, I got a copy of the burtnlatke on my desk, plexiglass with some copper pieces on it. 3 gaps over a 30cm strip. And I guess a few bolts wont hurt afterall heh.
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Unread postAuthor: stewart_1322 » Tue Apr 21, 2009 9:01 am

So I know about nothing about making spark strips and wasn't going to even use one until I read about them severally increasing performance. I put together this crud test to see if my 12KV grill zapper would jump 4 gaps good. It did. It has 4 gaps that are around 1/8". I tried to make some black lines to help show the gaps.

Does it look like it fits? I put the chamber in to compare it too. Its a 4"x24" reduction to 2".
Feed back? Criticism? Opinions?.......Help?

Image
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Unread postAuthor: inonickname » Tue Apr 21, 2009 9:39 am

Did you use an adhesive copper tape for that? that's what I use on mine, and it's brilliant. Gets destroyed if you use a camera flash without a coil though.

If not, I can recommend it. It's just a copper version of sticky tape that lead-lighters use to stick together bits of glass to solder. Also good for contact rails on homemade slotcar tracks.

That's what I used on this beast:

Image

Image
You can see the fan in the background, schrader valve bottom is top left and spark strip is top right. The strip is simply copper tape on perspex, with 3 gaps. The tape wraps around underneath for a streamlined connection. Seen as you have the space try mount in centrally, spaced equally along your chamber.

Next project will use a single strand of copper..but you'll have to wait to see that one.

There's not much to go wrong if you pre-test your parts, but serviceability is always a good thing.
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Unread postAuthor: stewart_1322 » Tue Apr 21, 2009 12:06 pm

Yes, that was adhesive copper tape. You can see the roll on the right part of my photo.

So if I were to only use a set of electrodes in the center and not spark strip at all, would it really hurt the performance?
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Unread postAuthor: Biopyro » Tue Apr 21, 2009 12:11 pm

It wouldn't be as good as what you have now, but without a way to measure it you pobably wouldn't notice the difference much.
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Unread postAuthor: stewart_1322 » Tue Apr 21, 2009 12:15 pm

So it would be an unnoticeable difference with out instruments to show a increase in combustion pressures?
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Unread postAuthor: Biopyro » Tue Apr 21, 2009 12:22 pm

You might notice it if you were looking out for it, and it does depend on the individual cannon. My chamber is fairly short, so I didn't notice it unless I objectively compared the power, but yours look much longer so you will find it more noticeable.

For the extra work it entails, or lack of it, it's definately worth doing.
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Unread postAuthor: theBOOM » Thu Jun 11, 2009 1:06 am

Yes I agree with biopyro a spark strip in this chamber is crucial since it is so long (24 inch?) nway... Plus the fun part about cannons is actually making them :D :D
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