|Nov 03, 2009, 06:12 AM|
Any thoughts on spark ignition ?
- Peizo-electric : you could mount a series of these spark generators (say, from cigarette lighters) on a disk. Each one would be pre-loaded & latched against the spring, & released as the disk turned. The disk would have a wiper-arm (similar to an auto distributor) which would line up with the wire leading to the cannon just as the spring was released.
- Points & coil : Perhaps a very small 6V coil from a motorbike (or a small transformer with few primary turns & lots of secondary turns) - the rotating disk could act as a distributor (as above) for the HV & also provide a synchronised momentary contact for 6-8V to the coil primary. Coil secondary HV is fed to the cannons via the distributor.
I reckon that the attraction of a spark approach would be the lack of maintenance in the cannons - nothing to burn out & replace. Just earth the barrel & have the HV applied to an insulated spike in the breech (with a spark gap of, say, 1/16" between it & the earthed barrel).
Food for thought ?
|Nov 03, 2009, 08:32 AM|
Spark Ignition for Guns
I looked at micro sized spark plugs (http://sparkplugs.morrisonandmarvin.com/). They were about $20 each. I talked to a guy about the use for guns - forget his name now and can't find the link -who builds mini engines. He said the plugs would foul and wouldn't fire. They have to be clean and precisely gapped. Given cost ($4 glo plugs are about my spend limit)and that feedback, I didn't look much farther, but it may be a great approach.
I played with peizo lighters. Never could figure how to adapt the mechanism to a barrel, specifically, how to provide the mechanical force required to trigger the spark. The unit I used took a lot of force to compress the button. But again, a potentially very good approach that I didn't pursue enough. We need some people more creative than me to figure some of this out.
|Nov 03, 2009, 12:47 PM|
Firing guns - Ignitors and Ignition Device
Previous post on this topic showed a diagram (pic 1) of a proposed ignitor. Pics 2 etc show the latest actual build. This looks like it's the approach I'm taking vs many other ignitor approaches. I'll detail the reasons in a future write up on this thread.
The big advantage from my perspective with this approach is that it eliminates $5 glow plugs that easily corrode and foul and have very sensitive voltage and current limits. It instead uses an easily made ignitor using nichrome resistance tape from an old toaster that is much tougher than the thin nichrome wire used in glow plugs and in previous attempts to build nichrome ignitors.
The toaster heater tape seems to be the key to this approach.
The wood end plug in the pics is temporary. I ordered some ceramic putty to cast the final end caps. The heater tape will be replaceable in a couple of minutes when it does burn out. The ignitor is heated with two NiMH D cells (nominal 2.8V). Cell rating needs to be 2500mAh or higher as heater tape pulls 3.5 to 4.5A. 5000mAh batts available on-line would be better.
More details later.
|Nov 03, 2009, 02:53 PM|
Man, I'd be a lot more comfortable if that plug was threaded... (but I love the idea for using the toaster ribbon!! It's on of those "hit my head on the wall it so damned obvious ideas!" Well done DanL!)
However that's not my main point in joining the thread...
Now, I refuse to be held responsible for what follows as playing with chemistry is tricky and dangerous at best and I am no chemist or pyrotechnician. It was just easier to play with things that went boom when I was a kid. Dabble at your own risk. (ps. there are TONS of pyro sites on the web with lots of interestingly dangerous recipes.)
OK so what are we looking for here...
Also, the only mention of a propellant I have seen is "black powder," which unfortunately covers a very great deal of territory. We talking large granule, slow burn; fast burn; composition? Or we talking Pyrodex or maybe homebrew...
Part of what we are trying to so here is actually retard the powder and make it inefficient as we are not trying to push a round down a barrel at maximum velocity. We are actually confronting the opposite of what a medieval gunner wanted. We want the maximum "burn" to occur outside the barrel to create smoke.
For those of you who didn't have a misspent childhood and without having to resort to Uncle Fester's Home Workshop Explosives, Second Edition or McLeans Do-It-Yourself Gunpowder Cookbook, the main issue is not the noise, but the visuals (e.g. a bit o'orange flash and a lot o'smoke hopefully smelling of her Majesty's right honorable brimstone) and that brings us to composition of the propellants.
OK, the basic chemistry of gunpowder is this, as everyone knows, 75% potassium nitrate (saltpeter), 15% charcoal (not kingsford); and 10% sulpher (For more, go here) The smaller the corn (granule size), the faster the burn.
The formula for a "smoke bomb" is basically 3 parts saltpeter and 2 parts sugar (sugar supplying both the carbon an oxygen as as an accelerent) and at proper proportions producing quite a volume of smoke. Baking power can be mixed in as a retardant, both to slow as well as cool the reaction.
So now our problems can be seen this way...
Now, how to keep things in order... that brings in an old friend from my junior-high and high school days... flash paper! (They let us play with it in class... within reason. ) I used to buy mine from the magic store around the corner from school.
(How to make flash paper... Haven't tried this, so can't vouch for it at all other than the video.)
Now flash paper stuck into a glow plug cannon, will make a pretty significant report all on it's own, so it's is possible that the fast burning propellant charge can be done away with in some cases (empirical experimentation is called for here...).
We got pretty fair results from a number of models, including re-barreled Tamyia Tigers and Shermans in addition to boats, using hand rolled cartridges of flash paper and talcum power or using cartridges with a small amount (a few grains) of flash and smoke powders. Again, most of the 'Propellent" charge was the first inch of flash paper which ignited the powder (if all worked right) just before it hit the muzzle creating a large volume of smoke from the powder burning inefficiently in an unconfined space.
In the tanks we used the friction of a six inch brass tube inside a another tightly fitted brass tube (made up of four sleeved tubes) as a recoil dampening system. Usually the inner tube only moved about an inch or so.
|Nov 03, 2009, 03:20 PM|
Firing guns, Black Powder
Craig, any more great info on pyro stuff???
Powder is Goex BP fffg. Tried Pyrodex and Trip 7. Not nearly as smoky and harder/less reliable ignition.
Can't wait to try powdered sugar...
Your # 1-2 objectives are a perfect summary of the design goals.
The wood plug is temporary. But I'm finding that IF SMALL charges in a SMALL diameter, SHORT barrel with NO PROJECTILE and soft FOAM wad giving little resistance and back pressure, that the plug doesn't blow.
This is still a new design. Plugs will likely be cast from ceramic putty and pressed in, sealed only with silicone or some other removeable adhesive.
If a plug blows aboard ship, it shouldn't cause a lot of damage. Note that these guns are intended to fire ONLY out on the water, well away from anyone.
Any idea how to make a threaded plug and get the loose leg of the heater tape to contact the grounded barrel wall??? Other plug capture methods???
|Nov 03, 2009, 04:06 PM|
For what we are doing, I'd say that we should stick to the real thing, good ol' black power perhaps partially substituting some sugar for the charcoal, with maybe a smidgen here and there of the smokeless powers used for handgun reloading. The rifle powers are slower burning. Either that of making some of the caramelized smoke bomb material and then milling it to power for inclusion in the charge.
The thing with the black power substitutes, many are designed to reduce visible smoke, just not as much as the smokeless powers. Just what we don't need.
Using flash-paper as the cartridge paper wrapper for the cartridge also serves in some ways as it's own wadding since, while it burns at a high rate of speed, the intact "projectile' end of the cartridge containing the "smoke charge" again serves as it's own wadding.
What about this... The firing plugs are threaded into the cannon bodies, however the ceramic putty surrounds the anode of the nichrome entering the center of the firing plug. It is then grounded to the body of the firing plug either with a bit of silver solder or by being crushed between wall of the cannon and the side of the plug. Either way, a good gas tight seal should be required... I have this thing about blow-back and gas leakage. If for no other reason than these have to be bench tested before they ever get mounted. I recommend having a nice 4x4 block in back of them during trials.
BTW, I ASSUME you have a lathe, yes??
Now, I refuse to be held responsible as playing with chemistry is tricky and dangerous at best and I am no chemist or pyrotechnician. It was just easier to play with things that went boom when I was a kid. Dabble at your own risk. (ps. there are TONS of pyro sites on the web with lots of interestingly dangerous recipes.)
|Nov 03, 2009, 05:27 PM|
This goes absolutely without saying! Safety, personal and range is number one concern.
|Nov 03, 2009, 06:09 PM|
Other than that you guys are way beyond my wood match heads in a 5/8 nut with two bolts threaded in and dropping it down a piece of pipe to make a mortar. I did manage to get into trouble with this thing when we were mortaring cars in a junk yard back in the early 50s--we broke some windshields that were valuable and my neighbor's dad got kind of nicked off at us.
|Nov 03, 2009, 07:58 PM|
|Nov 03, 2009, 11:18 PM|
One other thing just occurred to me, we may want to look at as well is "flash powder" as it releases a large quantity of smoke if not contained, though the use of aluminum powder gives it a distinctly blue-white flash color.
Basically that is what is used in most firecrackers, M-80s etc. these days. I wonder if there is a way to retard it a bit, get it to deliver more smoke...
|Nov 04, 2009, 12:27 AM|
Firing Guns for R/C Ship Models - Igniter and Switching Design
The best approach for ignition of multiple black powder guns for the 1/24 scale R/C brig Syren (a modified Steel, Chapman & Hutchinson model, www.modelsailingships.com) and similar models seems to be a heated resistance wire filament, made from nichrome “tape” from a toaster, triggered by a servo-operated rotary switch.
Numerous black powder ignition approaches were evaluated: glow-plugs, micro spark plugs, peizo-electric ignition, rocket igniters, steel wool conduction in a powder blend, and a variety of nichrome wire assemblies. Glow-plugs were costly (about $5 each), had a very narrow voltage operating range between too cool and burnout, collected powder residue in the filament well, corroded easily and had a somewhat slow coil heat up (relative to the rapid fire requirements of a full broadside). Glow plugs are successfully used in the current generation of guns, but an improvement has been made.
Spark plugs and peizo ignition system references note that fouling would be an issue with reliable spark generation, and fouling occurs rapidly in a black powder barrel. Also, envisioning and designing a system for mechanical activation of the peizo crystal for rapid multi-gun firing was beyond me.
Rocket ignitors would cost about seventy-five cents for every shot, adding up fast for multiple nine-gun broadsides. They are one-use, so would need to be replaced at each re-load, an undesirable additional step requiring access to the back of the gun vs. the muzzle alone for reload.
Steel wool strands mixed in to the powder charge and placed in a grounded barrel with a positive central electrode worked well – for one or two times in a new barrel. The slightest barrel and electrode fouling prevented the steel wool fibers from conducting and heating, thus preventing ignition of the powder charge.
Various diameters of nichrome wire were assembled into home-made “glow-plugs", but wire burnout and gun-to-gun variability were key issues.
Many variations of the above ideas have been proposed, but the devil is in the details. Getting reliable, uniform, rapid ignition of multiple guns (nine to eighteen guns) requires a robust igniter resistant to fouling effects, a reusable design (to minimize effort and time to re-load) a reliable and simple ignition distribution circuit, a reliable rapid switching device and a power supply matched to the heavy amp draw and voltage requirements of the igniters used.
The igniter design now being built and tested is shown in Figure 1. The rotary switching device design (for 17 guns) is shown in Figure 2. The igniter design allows very quick and cheap replacement of a burned out filament, provides direct contact of the filament to the powder and is flat faced and easy to clean. The use of nichrome heater “tape” from an old toaster is a huge improvement over any previously used round wire. The tape takes a wider voltage range without significant deformation or burnout. The resistance per unit length is also just right for the design length, providing very rapid heat- up to the powder ignition temperature at about 2.5 to 3 volts, but doesn’t burn out with a short duration application of up to about 6 volts.
System will be powered by two “D” cell NiMH batteries, rated at 5000mAh, providing about 2.8V under load at full charge. The high capacity batteries are necessary to minimize voltage sag at the high instantaneous current load, about 3 to 4+ amps, in this application.
Details, specifications and performance notes coming after the build and testing is completed.
NOTE: Triple Seven, Pyrodex, flash powder, flash paper, 1/8" dia. fuse, and small fireworks were all tried as charge materials. fffg black powder by far has given most reliable ignition and most smoke.
|Nov 07, 2009, 12:40 AM|
Hi Dan L, I like your idea for cannons, here's a idea you mite like, use a 1/4" pipe nipple 6" long and cut it in half, will make 2 cannons 3" long and 2 1/4" pipe caps, you could make up some extra wood plugs with the nichrome tape, if you need to change the igniter just unscrew the pipe cap, change the plug and screw the cap back on.
|Nov 08, 2009, 10:26 PM|
Firing Guns for R/C Ship Models - Igniter Design
Thanks for the idea. My first barrels were made with caps on threaded nipples as you show. Some of the problems I an into is that the thread is pipe thread (NPT), and is tapered. It doesn't tighten to the same endpoint, leaving different amounts of space between the end of the nipple and the inside base of the cap. Also, deposits build up in the dead space and are hard to clean out. The bolts are straight threads and the seating of the bolt into the barrel will be uniform for all guns.
The wood plug I'm using for the test rig is already burning at the tape contact point, making the contact point less solid.
Here's a sketch from previous posts showing some of the past history on using pipe caps.
Keep the ideas coming - this still isn't solved well enough.
|Nov 08, 2009, 11:43 PM|
DanL, I didn't mean for the threads to lock the cap on, I thought you would tighten the cap till the 2 brass nails came together, this would lock the whole thing together, also didn't relize that the wood plug wasn't working out, do you have a lathe, if so the plug could be made out of nylon and when pressed together it would seal.
|Nov 19, 2009, 10:21 PM|
Firing Gun Construction Pics
Here are a few pics of the construction process on the 16 gun system for Paratroopers' SC&H Surprise. Thanks to everybody that shared ideas - you can see that a lot of them were used in the final version. These guns are multi-use - the firing mechanism is relatively permanent. Barrel cleaning is done with a few squirts of Windex (or diluted sudsy ammonia cleaner), water rinse and Q-tip swab.
Load is wad of flash paper, black powder and a soft waterproof foam wad. Flash paper serves three purposes: reduces fouling on igniter, ignites even faster than BP,and serves as a safety feature. If gun has hot residue or is inadvertently electrically "hot", stuffing in the flashpaper wad results in just a slight "woof!!" vs. an explosion of the BP charge.
The igniter wire is 0.0159" nichrome, crimped on one side to a copper electrode that is insulated by a silicone sleeve. The other end is trapped between a groove on the breechbolt and the barrel threads.
Igniter is easily replaced, but failures should be minimal.
Very fast and sure ignition, unlike the glow plugs I was previously using. And all parts are now pretty corrosion resistant, unlike the glow plug bodies that corrroded quickly.
Not intended to be scale carronade models, they are a bit similar though in size and appearance.
Batteries are NiMH D cells, 1.5V. They are an amazing 10,000mAh capacity -important to heat the igniters in rapid succession without loosing their punch.
This series of guns has an ID of about 3/8" vs the 1/4" inside diameter of the smaller guns on Syren. The bigger guns put out a LOT more smoke and look acceptable sticking out the gunports.
Should be a good show when Ray gets them.
More details when system is finished.
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