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First spudgun :) Needing ignition help

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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Unread postAuthor: jackssmirkingrevenge » Mon Oct 20, 2008 1:06 pm

A bit of a sidenote but:

SEAKING9006 wrote:It was made about a year or two ago in response to a thread I made on spudtech about the construction of cartridge based combustions.


It was originally uploaded and posted here as part of the development of my combustion cartridge project, picture links are now dead but I had uploaded them on this forum here to keep them in the public domain :)
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Unread postAuthor: Silentone » Mon Oct 20, 2008 5:40 pm

jackssmirkingrevenge wrote:No need to use a capacitor, just hook up the two points of the piezo to your bolts.


The Piezo i had was a very weak spark.. is that all i need?

TurboSuper wrote:Your problem is simply that the caps don't have enough voltage behind them. They only have about 300V or so- not nearly enough to jump a gap.

You'd need to either wire the 3rd, really high voltage lead on the board in between them to ionize the air, or put some steel wool in between the electrodes. Or you can wire the caps to an ignition coil to step the voltage up to a few kV.

I'm with JSR though- go with a piezo. You don't need any fancy electronics whatsoever, just wire the two leads to your spark gap and you have an insta-kaboom :D

These Mickey-Mouse camera ignition circuits are usually more trouble than they're worth, the only real advantage I see to them is they make that cool sci-fi whining noise when the caps charge.


We removed that third wire as we thought it was just an earth, Ill solder that 3rd wire back on.. But in my setup where would i put that 3rd wire?

markfh11q wrote:Actually, they're good for making hybrid ignition systems, since you generally need more voltage. A camera capacitor dumping through a Nissan ignition coil made one of the biggest sparks I ever generated...


Does the ignition coil make more of a voltage?

jrrdw wrote:Go with the 100,000v stun gun circuit from www.bcarms.com :D


Stun-guns are illegal where i'm from, I'm from New Zealand

jimmy101 wrote:Like turbo said; you doubled up on the wrong capacitor. The big-ass cap is charged to 300~330V by the circuit board. That voltage will only jump a gap of about 0.2mm (~1/100"). There is a lot of energy in the cap but the voltage just isn't high enough to spark. (Two photocaps would contain about 12 joules of energy when fully charged.)

The high voltage (about 10KV) needed to trigger the phototube is created by dumping a second, much smaller cap (see photo), through the HV trigger transformer. The output of that transformer is carried by a wire to either the metal reflector around the flashtube or to a wire wrapped around the flashtube. That wire is the only source of high enough voltage to jump a gap. You can try to use that wire as the spark source. The other side of the gap would be wired to the circuit boards ground contact. Though the spark is up around 10KV the current is extremely low because the cap that supplies the power is only something like 0.02 MFD, total power when charged to 320V is 0.5millijoules (just barely enough to ignite propane+air).

So, it is that small cap that you might try doubling up using the cap from another board.

Or, dump the big-ass photocap through a car ignition coil. You might think you could dump the big-ass cap through the trigger transformer but I suspect you would destroy the transformer with that much power going through it.

Or, try a trigatron, which uses the two leads from the big-ass cap plus the HV lead in a three electrode spark gap. That'll give a huge spark, but is a PITA to keep working becuase the alignment is tricky and the electrodes get burned up.

Or, like others sugested, just use a BBQ piezo or buy a stungun.


So i should use a 3rd bolt and run it from that other spot where i had removed the 3rd wire (we thought it was just an earth) and create a T kind of alignment?

Stun guns are illegal here, I'm from New Zealand ;) My BBQ Piezo was very weak.. and ive made the holes for the bolts :(

Just to make sure i've read correctly..

ImageImage


Thanks for the feedback!, As i said before i'm not really to hot on electronics ;) Yet anyway..
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Unread postAuthor: TurboSuper » Mon Oct 20, 2008 5:52 pm

That third wire would either go in between the gap of the capacitor leads to act as a trigitron of sorts, or act as the spark itself by placing it near the ground.

I've never really tested this setup, but some dude got it working on a website I read.


And yes, even the small spark from the piezo will be enough to ignite the cannon...it don't take much.
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Unread postAuthor: Silentone » Mon Oct 20, 2008 5:59 pm

TurboSuper wrote:That third wire would either go in between the gap of the capacitor leads to act as a trigitron of sorts, or act as the spark itself by placing it near the ground.

I've never really tested this setup, but some dude got it working on a website I read.


And yes, even the small spark from the piezo will be enough to ignite the cannon...it don't take much.


How much spacing would i need?

Is this correct :)?

ImageImage

Thanks!
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Unread postAuthor: DYI » Mon Oct 20, 2008 6:34 pm

I also live in a country where self-defense is illegal, but you don't need to worry about getting a stungun from BCARMS to New Zealand, as he removes the case and ships the bare circuit, without a battery, as a voltage regulator. Technically, it's not illegal to bring the bare circuit through customs, only when it's in the case do you have a problem.

Discharging a low voltage cap (like the ones on a camera board) through an ignition coil is of use sometimes, but it's an overly bulky system for a basic combustion gun. Either use a BCARMS high voltage pulsed DC circuit, or a basic piezo sparker for starters. Unless you're building an EBW or Marx generator to set off a high-mix hybrid, capacitor based systems are kind of overkill.
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Unread postAuthor: iisthemuffin » Mon Oct 20, 2008 6:38 pm

Im pretty sure it doesnt matter how big of a spark you create.

Think of it like this: If you have a towel soaked in gasoline and you light it with a lighter it will light just like if you lit it with a big propane torch.

Your not trying to make a huge spark. Just burn the fuel. If your ignitor is sparking, then it will catch the fuel inside of the chamber and your good to go.

If i were you i would just leave out the capacitors all together as JSR said.

The tiny sparker coming from the sparker is enough to igntie your fuel. Just make your gap a bit bigger and you should be fine.
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Unread postAuthor: Silentone » Mon Oct 20, 2008 7:03 pm

DYI wrote:I also live in a country where self-defense is illegal, but you don't need to worry about getting a stungun from BCARMS to New Zealand, as he removes the case and ships the bare circuit, without a battery, as a voltage regulator. Technically, it's not illegal to bring the bare circuit through customs, only when it's in the case do you have a problem.

Discharging a low voltage cap (like the ones on a camera board) through an ignition coil is of use sometimes, but it's an overly bulky system for a basic combustion gun. Either use a BCARMS high voltage pulsed DC circuit, or a basic piezo sparker for starters. Unless you're building an EBW or Marx generator to set off a high-mix hybrid, capacitor based systems are kind of overkill.


And just make a case? It sounds like youve done this before :P

iisthemuffin wrote:Im pretty sure it doesnt matter how big of a spark you create.

Think of it like this: If you have a towel soaked in gasoline and you light it with a lighter it will light just like if you lit it with a big propane torch.

Your not trying to make a huge spark. Just burn the fuel. If your ignitor is sparking, then it will catch the fuel inside of the chamber and your good to go.

If i were you i would just leave out the capacitors all together as JSR said.

The tiny sparker coming from the sparker is enough to igntie your fuel. Just make your gap a bit bigger and you should be fine.


How would i wire in the Piezo? As now i have the holes from the bolts? Just poke in the wire from the piezo?
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Unread postAuthor: DYI » Mon Oct 20, 2008 7:16 pm

How would i wire in the Piezo? As now i have the holes from the bolts? Just poke in the wire from the piezo?


There are two contacts on a piezo sparker, one obvious, and one not-so-obvious. The first one is the wire that protrudes out the bottom of it, and the second is a recessed wire that runs along its length that usually makes makes contact with the metal of the barbeque to complete the circuit.

And just make a case? It sounds like youve done this before


It was what I first used on my hybrids, before the precharge pressures got high enough to make high voltage arc ignition impractical. It also made for some great entertainment, after I made a decent, solid case for it :wink:
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Unread postAuthor: iisthemuffin » Mon Oct 20, 2008 7:34 pm

As DYI said, there should be wire sticking out already. that is your first contact. And then along the side there is a metal contact. Just solder another wire to this contact. If there is no wire coming from the bottom and just a metal pin jsut solder a wire to that.

Then wrap your two wires from your ignitor around your screws. One on each screw. Spread your gap out a little as said before. Click and see if you have a psark jumping. But make sure your chamber is free of fuel when you click the ignitor because im sure you like your eyebrows right where they are.

Here is a link to better explain things for you:
http://www.neospud.com/piezo.html
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Unread postAuthor: ammosmoke » Mon Oct 20, 2008 10:28 pm

Actually, a bigger spark/more ignition locations is more effecient and therefore more powerful. But, this being a simple gun and a first timer, I don't think I would bother.
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Unread postAuthor: MrCrowley » Mon Oct 20, 2008 11:46 pm

Stun guns are illegal here, I'm from New Zealand

Same here, didn't stop me.

As DYI said, I just got one ordered from BCARMS, which he posts as some sort of TV circuit I think. You then just put it in a project box. As far as the police are aware, it's just a high voltage circuit.


BTW combustions are highly illegal in NZ. $4000 fine and possible prision sentence. Pneumatics are fine as long as you don't do anything stupid with them and you are over 18.
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Unread postAuthor: Silentone » Tue Oct 21, 2008 2:12 am

Right i've wired up the Piezo starter.. It sparks fine..

I put in the potato *grin* and did a 2 second spray of deodorant and put on the end cap.. Clicked the piezo but no joy, Any ideas?

Something i can do to make it work? Too much deodorant? Not strong enough spark?
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 21, 2008 4:37 am

Silentone wrote:Something i can do to make it work? Too much deodorant? Not strong enough spark?


2 seconds sounds like far too much, half a second should suffice as your chamber is relatively small. Also, why deoderant when you can use propane or butane? if anything, use starting fluid ;)
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Unread postAuthor: iisthemuffin » Tue Oct 21, 2008 10:18 am

Silentone wrote:Right i've wired up the Piezo starter.. It sparks fine..

I put in the potato *grin* and did a 2 second spray of deodorant and put on the end cap.. Clicked the piezo but no joy, Any ideas?

Something i can do to make it work? Too much deodorant? Not strong enough spark?



Just toy with the amount of fuel you use. And also make sure the deoderant you are using is actully flamable. Alot of aerosol sprays arent.

Just start with a quick spray and then try to fire. If nothing happens try a little more or less until you get it right.
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Unread postAuthor: jimmy101 » Tue Oct 21, 2008 12:10 pm

ammosmoke wrote:Actually, a bigger spark/more ignition locations is more effecient and therefore more powerful. But, this being a simple gun and a first timer, I don't think I would bother.

Only part of that statement is true. For a single spark you need a milljoule or so of energy to ignite propane in air. Putting 5,000mJ in the spark will not change the performance of the gun. If you can see the spark it has enough energy to ignite the fuel. More energy in the spark doesn't help. Using these numbers the extra ~4,999mJ of energy will end of partly in the kinetic energy of the round. But 4,999mJ is a trivial amount of energy compared to the KE of most spudguns. A 100g spud at 300 FPS (~100m/s) has a KE of 500,000mJ. So the big-ass spark only added about 1% to the KE. (Acutally it'll probably only add about 0.1% since spudguns as heat engines are only about 10% efficient.)

Multiple spark gaps are a different story. If the gaps are well seperated then they will indeed increase the performance of the gun, mostly by significantly increasing the fuel's burn rate.
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