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First Cannon, love it, but want better.

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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First Cannon, love it, but want better.

Unread postAuthor: Imkindofabigdeal » Sat Nov 06, 2010 1:37 pm

Hey everyone,
First time post, but have pretty good knowledge of cannons (read a ton before I built my first one). I have a few questions:

1. How do you power the fan? And is it really necessary?
2. Can someone please explain the whole ratio situation for me? I really dont understand that still.
3. Is there any way to unglue the PVC? I used primer then glue and I want to be able to disassemble it and replace the actual pipe, but dont want to replace the joints, they are a bit costly.
4. What is the best vapor for everyone here?
5. Is there a way to make a quick vapor injector? I spray mine, but then take a few seconds to get the cap on. When my buddy helps me spray, I get a much better shot off.

Thanks everyone,
Ben
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Unread postAuthor: SpudFarm » Sat Nov 06, 2010 2:06 pm

Hello, and welcome!

1- Fans is powered by a 9v battery in most cases, usually with a switch and a box of some sort to house the setup in. A fan is not a must but helps performance.
2- Ratio is just the difference in volume between the chamber and the barrel. For a combustion the optimal ratio is about 0.8/1 where the chamber is the smallest IIRC.
3- No.
4- Propane and MAPP gas is used alot, usually metered. But starting fluid is pretty agressive for a spray and pray.
5- Look up propane meters, they are quite simple and accurate.

Just a quick answer, I am in a hurry.
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Unread postAuthor: Imkindofabigdeal » Sat Nov 06, 2010 2:09 pm

Thanks Spudfarm. Useful stuff there. If anyone can just give me some reference links for this I would gladly appreaciate it. Also can anyone go a little further into the ratio. Still dont understand it. I dont know why, but i feel like an idiot.

Thanks,
Ben
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Unread postAuthor: kjjohn » Sat Nov 06, 2010 2:11 pm

Welcome to Spudfiles!

1. You can power a standard 12v computer fan with a 9v battery, though I prefer to use rechargeable RC batteries. It sounds like you are using a spray n pray, so a fan probably isn't going to make much of a performance difference, but you mentioned ratios and "vapor injectors", so this leads me to believe that you intend to meter some kind of fuel such as propane. When using precisely metered fuel, a fan does provide an increase in performance.

2. The ratio is just the difference between chamber and barrel volume.

3. I have had to "unglue" PVC once, but it really only works, at least in my experience, when the glue hasn't dried yet. Once PVC solvent dries, it basically creates a chemical weld between the fitting and the pipe, in other words, they become fused together.

4. Propane is the best fuel, and MAPP gas can give a slight power boost.

5. Look this up on the wiki. Metering propane or MAPP is very easy, and doesn't require many parts.

Hope you are successful. Remember, the wiki is very useful, and you should find answers to most of these questions there.

EDIT: Just finished posting this, then realized SpudFarm beat me to it! Anyway, I basically said the same thing. But really, go check the SpudWiki. It will answer most of your questions.
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Unread postAuthor: Hubb » Sat Nov 06, 2010 4:01 pm

It sounds like you are using a spray n pray, so a fan probably isn't going to make much of a performance difference
On the contrary, I've had the most performance increase when using a fan in a spray n pray. Since these launchers are fueled by an unmeasured source, the fan helps to even things out. In a metered launcher, the performance gain is still there but it is more noticeable in the unmetered launcher.

To take this a step further, leave the fan on during the combustion process to generate more turbulence...

Propane is the best fuel, and MAPP gas can give a slight power boost.
Agreed. Propane, IMHO, is a superior fuel than MAPP because the power increase of MAPP over propane is just slight, but the cost increase of MAPP over propane is not. In other words, MAPP is not really worth the extra cost.

A ratio is usually read as chamber to barrel. In SpudFarm's example (which is the one most commonly sought after), it says .8:1, which means that the chamber is .8 times the volume of the barrel (if the barrel is 100 cu in, then the chamber will be 80 cu in).
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Unread postAuthor: Zeus » Sat Nov 06, 2010 5:44 pm

PVC fittings are partially disolved by the glue, then they fuse and harden, they don't come apart again.

That's how I understand it anyways.
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Unread postAuthor: SpudFarm » Sat Nov 06, 2010 6:53 pm

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