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I've been lurking long enough - time to go legit.
I've made two spud guns with the advice gathered here and elsewhere.
I've been using the VIPERTEK VTS-880 Stun guns found on ebay for about ten dollars or so for ignition sources.
What's nice about these is that they are small, and the HV circuit is in a sealed cube. The arc is HUGE. They run on 5 - 6 volts.
I gut out the battery, switch, etc and add a connector for the battery. The whole thing - case, spark gap and all fits nicely inside a three inch or larger chamber.
Ive sawn apart a case to slim it down and fit it inside a two inch chamber.
Today's project is sawing off the top to get the spark gap, placing the spark gap inside the 1.5 inch chamber and using the rest of the case as the handle, providing me a trigger, safety switch, and power for the 5 volt chamber fan. Neat, clean and small!
The two guns I've made so far are excellent - really great firing at about 460 fps ( thanks, HGDT! ).
The little pistol won't be so fast, but still a lot of fun.
#1 - The Canon - 3" x 28" chamber, two 1.5" barrels 60"and 120" long.
#2 - The Rifle - 2" x 8" chamber, 3/4" x 36" barrel 'over and under' design.
#3 ( in progress ) The Pistol - 1.5" x 3" chamber, 1/2 x 8" barrel.
Pics to follow when I'm not too busy or plain lazy.
Thanks to all of you for lots of great ideas!
The cannon uses a propane metering system connected with an air tool quick release coupler. Much lighter to handle that way - it already looks pretty goofy with the 10 foot barrel attached.
The rifle uses butane measured by a syringe. The pistol will be the same.
The cannon and rifle use little 1/4 inch ball valves on the fuel inlets. The pistol will have a butterfly head screw in the rear cap.
You'll probably be disappointed with pistol performance though, 1x combustions do not scale down well since their peak pressure is fairly low. Have you thought of going hybrid? 2-3x should be safe in a well made PVC chamber.
I ran HGDT for the pistol - 246 FPS. Not nearly as fast as it's bigger brothers, but it will make my son happy.
I fooled around thinking about a hybrid, but I went for simplicity.
The cannon at 4x/90 psi should deliver a supersonic spud - or else mashed potato spray. That might be interesting...
3" pvc schd40 min burst is 840psi. HGDT shows 288 psi. I think I still wouldn't want this on my shoulder when I pulled the trigger.
Well, my hybrid with 45cl chamber and little over 1"x40" barrel at 10x will make potato smash...
Est Sularus Oth Mithas
10x - Yikes!
I suspect your potato disintegrates almost instantly.
And then scorches on to the inside of the barrel.
I'd love to see it, though.
$9.79 with free shipping. Save money buying several at at time - I got a three pack for $26.00
I don't have any relationship with this seller - other than repeat customer. There are several sellers with this item.
This kicks butt on BBQ grill ignitors.
Stun guns are not legal in all states or even the particular county or city you live in. Check 1st before you order...
When life gives you lemons...throw them back they suck!
'Tis true. Most of the sellers have a list of restricted locations in their ad.
If a friend were to disassemble the stun gun and send you the HV unit, it could then be considered an ignitor. It is no longer a stun gun any more.
Only sort of. I've used both and both have strengths and weaknesses.
Both tend to have limited lifetimes but in my experience the piezo lasts longer (I suspect few others have had the same experience). The problem with the stun gun is it's just too damn cool to watch the spark so you're firing it constantly. These cheap stun guns were basically designed to never be fired. The internal trigger gap is kind of marginal and tends to stop working after a while. Or some other internal component like a transistor gets cooked.
As others have pointed out stun guns are illegal in lots of places. Even where they are legal where you use it (or even where you have it) can make an otherwise legal stun gun illegal. In many places just walking into a park with a stun gun would be illegal. Put one in the trunk of your car and park in a school parking lot and you've probably broken the law. Piezos don't have that problem (unless they are obviously part of a gun).
Stun guns require a battery and are a lot bigger than a piezo.
A piezo itself is usually a pretty ergonomic trigger, you don't need to add anything except a mount. the BBQ piezos fit nicely into a piece of 3/4" (or 1/2"?) pvc so it is easy to build a reasonably ergonomic pistol grip that completely contains the ignition system.
Both will ignite a properly fueled gun 100% of the time if they are connected to a proper spark gap. Occasionally you get a bad piezo (or a bad stun gun) that never works very well.
For me, the only really noticeable advantage of a stun gun is that they are much more forgiving on the size of the spark gap, anything from 1/8" up to an inch (or more) will usually work.
Stun guns are much more hazardous to the user than is a piezo. A stun gun fires as long as the trigger is pulled. If the arm/hand/finger that is pulling the trigger gets into the HV circuit you might not be able to let go of the trigger. That would be a most unpleasant experience. A piezo gives a pulse then turns off. I don't think anyone has ever been killed by a piezo. People have been killed by stun guns.
I agree that the stun guns are cool, and can be as cheap or cheaper than a piezo, but there are times when they are the wrong choice.
p.s. Welcome to the board TedC. Post some photos
I do like the simplicity of a piezo ignition. I figured I already needed a battery for the fan, so a stun gun seemed to be a reasonable choice.
I tried piezos from lighters, and they are pretty unreliable and weak. I never did try the larger piezo units found in gas grills.
The BBQ grill ignitor I was comparing it to in my post above is the battery powered electrical type. I'm sure they work fine, but this has a far larger spark, and comes with the spark gap built in!
I think the monster spark helps create a really effective flame front, and it will light anything even remotely explosive. These guns really have a sharp crack when they fire. If it wasn't for the fact that I have 900 acres of woods behind me, and my neighbors also fire their rifles in their back yards, I would probably be getting a visit from the sheriff.
Regarding reliability - I think your probably right about these units frying with any kind of abuse. I've shown it off a few times, but they live inside the chambers of the guns, so there's not much to see anymore. So far - no failures.
I had considered using a simple 'one shot' circuit using a 555 timer, but after using the gun for a while, I've found that there hasn't been a problem with excessive triggering.
I'm glad to hear you've had luck with a piezo. I'll put it back on my list for consideration.
Is there any particular type that you prefer?
Rainy weekend coming up. Perhaps time to take pictures! Along with the other 20 things on the 'Honey do' list...
I like the BBQ ones. Mostly because they are in a case and have a button. I have extracted the piezo from lighters but what you end up with generally requires some work to get it mounted in something to make it practical as a trigger.
Besides the BBQ piezos (and like you said the battery operated ones are also good and just slightly more expensive) I've had some luck with hacking long handled butane lighters. Basically the handle + piezo part is left as is giving a reasonably ergonomic trigger + handle/grip.
The key for piezos is to use a sharp points in the spark gap. I like fine thread drywall screws or fine wire.
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