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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: chenslee » Fri Jan 30, 2009 1:03 am

I cut the bolt tonight. The rest of the gun is going to be drilling holes and ordering parts (the easy stuff)

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Here is the parts pile including the regulator attached to the propane adapter, the pin valves and the grill ignitor.

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Unread postAuthor: Lentamentalisk » Fri Jan 30, 2009 1:13 am

That bolt is overly well made. Honestly, in a combustion, you really don't need o-ring seals, but they most definitely will not hurt.
One thing you may want to consider, depending on how tight the balls are in the barrel, is some little friction contraption, or something of the sort to keep them from rolling out of the barrel. My experience with tennis balls in the past is that that has not been an issue, though.
I love it when new members, with access to great equipment put out quality projects. I can't wait to see the final product!
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Unread postAuthor: chenslee » Fri Jan 30, 2009 1:37 am

Lentamentalisk wrote:That bolt is overly well made. Honestly, in a combustion, you really don't need o-ring seals, but they most definitely will not hurt.
One thing you may want to consider, depending on how tight the balls are in the barrel, is some little friction contraption, or something of the sort to keep them from rolling out of the barrel. My experience with tennis balls in the past is that that has not been an issue, though.
I love it when new members, with access to great equipment put out quality projects. I can't wait to see the final product!


Thanks!! I browsed though here while doing research and I can't believe I didn't sign up then. There is a metric crap ton of information here.

Tennis balls are 2.5" I haven't measured them, but I think that is to the average of the fuzz. The cylinder bodies are 2.505 and the tennis balls are perfectly snug. No chance of them falling out, but no chance of them getting stuck. The nice thing about the cylinder bodies is a) they have ears that are tapped for mounting to, and b) they are hard anodized and polished on the inside, like super slick.

he bolt is turned down from 2.520 to 2.480. The orings are there really to keep the bolt from flopping around. I cut the groove on the second one too narrow and it does not fit in the chamber. More on that later.

The bolt is burly because a) I needed some meat to make o-ring grooves and b) 2.5" OD x 1/4" wall aluminum tube was cheap on ebay. The cylinder bodies are 1/8 wall.
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Unread postAuthor: Lentamentalisk » Fri Jan 30, 2009 1:49 am

Another issue I just realized, is that now that you are not using the torch head, you will have to deal with getting fresh air into the chamber.
I don't remember you saying anything about how you are going to deal with that, and seeing as that is the biggest problem that we have faced, here on SF, when it comes to rapid fire combustions, I was wondering what you are planning to do about that.
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Unread postAuthor: psycix » Fri Jan 30, 2009 7:52 am

I've never thought about it to use such a cylinder as part of a spudgun. They should be great as barrel or piston sliding tube (super smooth inside).
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Unread postAuthor: chenslee » Fri Jan 30, 2009 10:26 am

Lentamentalisk wrote:Another issue I just realized, is that now that you are not using the torch head, you will have to deal with getting fresh air into the chamber.
I don't remember you saying anything about how you are going to deal with that, and seeing as that is the biggest problem that we have faced, here on SF, when it comes to rapid fire combustions, I was wondering what you are planning to do about that.


I'm worried about it too. I want to see how it runs first before I spend the extra money on a solution. Considering that a portion of the combustion chamber slides back to accept balls, It's going to take a considerable gulp of air.

If I have problems with mixing or stale gasses, I'll put an air cylinder with check valves on the side that pumps air in when the bolt is cycled.

I'm not putting a fan in it.

Here's a pic of the model with the a 4" stroke air purge cylinder.

Image

All the pics I've put up so far are of Rev.5. I've moved on to Rev.6 with slightly re-arranged componentry but the plates get designed last so they are not as pretty as Rev.5's

I'll throw up a cross-section soon to explain the action.
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Unread postAuthor: Combustion Monkey » Fri Jan 30, 2009 4:26 pm

I think this has a ton of potential! Very much looking forward to updates and the working version. I would love to make a golf ball version of something like this. The concept makes my advanced combustion look like a spray and pray.
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Unread postAuthor: chenslee » Fri Jan 30, 2009 5:10 pm

The underlying spirit of making spud guns is "use what ya got".

I've been kicking around the idea of some sort of non-pvc, non potato bolt loader for years. My first idea centered around using soda cans. Unfortunately, soda cans have a weird OD with no barrel options.

Next idea was a 40mm ping pong ball CO2 electro-pneumatic that would have used a 24v programmable logic controller to time the cocking and firing. Estimated costs were around $1200, and I wasn't even sure if a 40mm ping pong ball would fit in a 40 mm bore cylinder.

I settled on the 2.5" bore propane tennis ball gun because a) I happen to have some junk 2.5" bore cylinders laying around, b) tennis balls are fuzzy and compressible unlike ping pong balls, and c) propane is much cheaper per shot than C02.

The plates will be made from 1/8" aluminum plate and will be water jet cut at a local machine shop. The structural aluminum is 8020 and is fairly inexpensive (like $0.13 per inch), and it just so happens I talked to the sales rep today and secured a PHAT 35% discount on 8020 stuff.

Anyway. I had some plates cut to make an all-in-one rig for my xbox and they came out real nice. Water jet cutting is basically like printing on aluminum. I give them an autocad file and *bing* out pops my part. This is why the plates are the absolute last thing to buy. A minor change in a component position is no big deal....until the holes become real.
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Unread postAuthor: mega_swordman » Fri Jan 30, 2009 10:25 pm

chenslee wrote:I give them an autocad file and *bing* out pops my part. This is why the plates are the absolute last thing to buy. A minor change in a component position is no big deal....until the holes become real.


I can confirm this last statement. I work on a robotics team and know all too well that the robot always looks fine on solidworks until we make a hole a fraction of a centimeter off.

Anyway, I'm looking forward to seeing the finished product.
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Unread postAuthor: chenslee » Sat Jan 31, 2009 4:56 am

mega_swordman wrote:
chenslee wrote:I give them an autocad file and *bing* out pops my part. This is why the plates are the absolute last thing to buy. A minor change in a component position is no big deal....until the holes become real.


I can confirm this last statement. I work on a robotics team and know all too well that the robot always looks fine on solidworks until we make a hole a fraction of a centimeter off.

Anyway, I'm looking forward to seeing the finished product.


I love this place more and more. I'm the robotics field too.
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Unread postAuthor: inonickname » Sat Jan 31, 2009 6:33 am

I'd love to see what comes out, and I'm sure you'll figure something to fix the stale gas issue.
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Unread postAuthor: psycix » Mon Feb 02, 2009 10:19 am

chenslee wrote: Unfortunately, soda cans have a weird OD with no barrel options....
Next idea was a 40mm ping pong ball....
I settled on the 2.5" bore propane tennis ball gun because...

Maybe a little late but...
When looking for ammo of those sizes, may I recommend you the golfball. A very consistent shape with (WAY) more sectional density then a tennis ball and... dimples. One of the best range projectiles and also good on punching 2" holes through stuff. Tennis balls are too light to do damage or to fly far, they're certainly not the best projectiles. Golf balls should be just as available as tennis balls and are easy to load.
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Unread postAuthor: Mongloid » Mon Feb 02, 2009 12:38 pm

chenslee wrote:I want it to be non-lethal. It hurts less when my friends inevitably "accidentally" shoot me with it.


Y u no use golfballz ?!?!11
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Unread postAuthor: starman » Mon Feb 02, 2009 1:43 pm

Mongloid wrote:
chenslee wrote:I want it to be non-lethal. It hurts less when my friends inevitably "accidentally" shoot me with it.


Y u no use golfballz ?!?!11


Hey Mongloid, try again. This isn't cellphone text world here.
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Unread postAuthor: Ragnarok » Mon Feb 02, 2009 2:19 pm

chenslee wrote:I want it to be non-lethal. It hurts less when my friends inevitably "accidentally" shoot me with it.

Might I offer the wise advice that if your friends cannot be given and follow a simple instruction like "Don't EVER point or shoot this at any person or animal, it could kill them", they should not be offered the opportunity to use it?

I have had friends use my cannons, but no-one I wouldn't utterly trust to be sensible, and even then I've made sure that they understand that they must treat it as being as dangerous as a shotgun.

Unfortunately, a lot of people suffer from the "I didn't think paintballs/potatoes/tennis balls could be dangerous" syndrome, even if it's only subconscious. As such, I always violently snap people out of these views with graphic demonstrations before they even touch my launchers.

To date, no-one has ever pissed about with my launchers. (And should anyone be stupid enough to, they will never get a second chance).
I suggest you take the same precautions with whoever you let touch your launchers.
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