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'Glow Plug' Igniter -(5/19) now with LARGE pics on page 2

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: timmeh87 » Mon May 19, 2008 8:07 pm

We worked on it some more today, and built a 'battery box' to house a few switches and a battery.

We used a 14-cell, 16.8v Ni-Cd battery. Its rated for 10Ah, but it fully discharges in about a week... making it less useful. Whatever though, you can put a useful charge into it in less than an hour.

The following image shows the completed box. The small switch controls a chamber fan, and the large switch is connected to the igniter coil (it won the "most satisfying click" contest). A handle serves as both a switch guard and an easy way to move the box, which weighs about 10 pounds.
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There is direct access to the terminals for charging
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The insides are quite simple, a switch for the fan, a switch for the coil, one common wire.
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An extra piece of nichrome wire
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So this is the back end of the cannon. Yes, the design is messed up. The propane still isnt metered. We just spray it in the end of the hose. I guess a meter is the next project. The screws for the igniter coil used to be a "spark gap". Also you can see my power supply, which can power the cannon, charge the battery, or both :D.
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No math was done in the construction of this cannon. The barrel is just the 6 foot piece that we originally bought. The chamber is like 2.5 feet. :dontknow:
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Inside the bottom half
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With the igniter turned on
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Unread postAuthor: DYI » Mon May 19, 2008 8:23 pm

What kind of delay is there between pressing the trigger and ignition? Seems like something that could take a few seconds to warm up.
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Unread postAuthor: timmeh87 » Mon May 19, 2008 8:29 pm

Yes, I discussed this earlier.

We originally designed a coil for 12v, which took about 4 seconds to heat up. When we moved to the 17v battery, the same coil heated up in less than 1 second. However, it reached critical meltdown temperature in about 3, and it did not survive the testing phase.

The current coil is too large and takes about 6 seconds to heat up. We plan to start twisting the coil in places to create shorts and gradually fine tune it to just the right length for continuous operation and fast start-up.

I have also been entertaining ideas in my head of some kind of electronic system that could send short bursts of incredibly high power to fire instantly without burning out the element... 555 timer style.
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Unread postAuthor: starman » Mon May 19, 2008 8:37 pm

Uhh yeah, slow and big....and uhhh, heavy... Kind of Wile E. Coyote-ish, so some cool points for that. However, I can't imagine this is in any way better than, say a BBQ ignitor, or lantern lighter or stun gun or even a match hole.
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Unread postAuthor: timmeh87 » Mon May 19, 2008 8:47 pm

Well we actually tried a match hole, and went through several bbq igniters that broke. Im not sure that you can just buy stun guns that easily up here in Canada. :P. Sure ebay or what have you, But this cost us $0 and the cannon takes like 2 minutes to reload anyways. Its not like we are going to be chasing deer with it.

Plus I have evil plans to make some H2/O2 out of some water. (Dont bother taking the tread off-topic and warning me about that). I would prefer to be about 6 feet away when testing that.
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Unread postAuthor: starman » Mon May 19, 2008 9:11 pm

timmeh87 wrote:Well we actually tried a match hole, and went through several bbq igniters that broke. Im not sure that you can just buy stun guns that easily up here in Canada.


BCarms will sell you a stun gun, guts ripped out of the case, and sold as high voltage circuit for Canadian port of entry issues....this works just fine.

If mounted properly, a BBQ ignitor should last the life of the average spudder. How were you mounting it?
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Unread postAuthor: timmeh87 » Mon May 19, 2008 9:46 pm

Crappily apparently. Our spark gaps were probably way too large. There was duct tape on everything (there still is)

Anyways the closest we are getting to a spark would be an ignition coil, running off of the same battery. I like the sound of this a lot better. Piezoelectric is way too wimpy. Pretend Im Tim Allen from Home Improvement. More power ugh ugh ugh. I want to build it myself.

Think of this more as a technology testbed than a particularly useful cannon :lol:

Plus like I said. I would like to be able to stand WAY back anyways.
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Unread postAuthor: Boom_erang » Tue May 20, 2008 9:40 am

timmeh87 wrote:Piezoelectric is way too wimpy. Pretend Im Tim Allen from Home Improvement. More power ugh ugh ugh. I want to build it myself.


LOL - nice image. I disagree about Piezo being "wimpy" however. All my cannons use them and they have been great so far.

-B
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Unread postAuthor: timmeh87 » Tue May 20, 2008 10:07 pm

Small update: we got fed up and switched our fuel from propane to quick-start (diethly ether and aliphatic naptha). The gun now shoots potatoes a few hundred meters with near 100% reliability.

It cost $5 for a spray can that will probably last longer than anyones interest in the gun.
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