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FANG 2 thoughts

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: daberno123 » Tue Mar 10, 2009 3:10 pm

btrettel wrote:There also is the problem of choosing an advancement mechanism... something I'd rather put off until later.


Have you looked into the Mauser Zig-Zag Style of revolvers? It's the same design that Solar's Eclipse uses if I remember correctly.

The system would be reasonably easy to implement. All you would need is an air cylinder with some sort of pawl to ride the zig-zag grooves on the revolving barrel assembly.
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Unread postAuthor: btrettel » Tue Mar 10, 2009 3:21 pm

Long barrels are associated with long range accuracy because a long barrel usually means high velocity and this results in a flatter trajectory. The projectile gets to the target quicker and therefore has less time to be affected by gravity, wind and other environmental factors which have to be compensated for.


Very true. I neglected to mention that because my simulation will keep muzzle velocity constant. It'd be worth noting for others less scientific than myself though.

The other side of the coin however is that with a longer barrel, there's more time in between you pulling the trigger and the projectile leaving the muzzle, so any movement during that time is more likely to have a negative effect on your accuracy.


Good point. This is another reason to use shorter barrels, especially given that the time in barrel is actually reduced more than the barrel length would suggest (keeping muzzle velocity constant) because of other factors (the higher pressure with shorter barrel lengths primarily).

Have you looked into the Mauser Zig-Zag Style of revolvers? It's the same design that Solar's Eclipse uses if I remember correctly.

The system would be reasonably easy to implement. All you would need is an air cylinder with some sort of pawl to ride the zig-zag grooves on the revolving barrel assembly.


That is the plan at the moment, but I was also considering some similar mechanisms seen in other Nerf guns that are simpler.

Below are some close-ups and descriptions of the pieces made. Sorry if the contrast seems a little high--I screw around with the curves too much.

Image

You couldn't tell at all what this piece was in the original photo. It's meant to be attached to the air reservoir and allow the trigger/valve assembly to be held in place (the holes are for screws). Originally I wanted to wrap a big piece of plastic around the air reservoir... but that would have been expensive so I switched to velcro, which actually is a much better idea.

Image

These pieces basically attach the rotating barrel assembly (commonly called a "turret" in the Nerf world) to the valve and a polycarbonate structure that I have not made yet. The turret piece will be held in with a spring and bolt that are not shown. A thrust bearing will prevent unthreading of the bolt.

Image

The left piece is a stabilizer for the turret. The right piece is simply a trigger.
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Unread postAuthor: PVC Arsenal 17 » Tue Mar 10, 2009 3:58 pm

Looks like an excellent start there! How did you manufacture those parts?
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Unread postAuthor: btrettel » Tue Mar 10, 2009 4:20 pm

As I said earlier, fused deposition modeling was used. It's basically a machine that shoots a stream of melted plastic into a shape. The process is a little more complicated than that if you have overhangs (as I did), but that's the gist.
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Unread postAuthor: POLAND_SPUD » Tue Mar 10, 2009 4:29 pm

As I said earlier, fused deposition modeling was used


ohhh sorry for hijacking the thread but is it something like the reprap project or fab@home ??

BTW nice parts

EDIT
sorry, I didn't notice your post on the first page

BTW no 2 Am I the only one who thinks that The reprap and fab@home are like a gift from heavens for us ?? lol in 5 years time they should improve them to such an extend that they could produce almost as good parts as yours
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Last edited by POLAND_SPUD on Tue Mar 10, 2009 4:49 pm, edited 2 times in total.
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Unread postAuthor: btrettel » Tue Mar 10, 2009 4:36 pm

Yes, FDM is the same method RepRap and Fab@Home use as far as I know.

Edit:

To respond to your edit POLAND_SPUD, I'd highly doubt any home built device made in the next couple years could get close to the system that produced my parts. I don't have much knowledge about this subject, but I do know that homebuilt prototypers use a much weaker plastic, can not do overhangs (unless they've improved that since I last looked), and have very significantly worse tolerances. I'd certainly be interested in having one, but it's not a holy grail, just another tool.
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Unread postAuthor: daberno123 » Wed Mar 11, 2009 4:08 pm

How is that cylinder you got from Catalina? Were you able to get one with NPT threads?

How big is it and how much did it cost?

I might look into getting one for a combustion cannon. Do you think they could make one with a larger thread size like 2" or even 3"?
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Unread postAuthor: btrettel » Wed Mar 11, 2009 5:17 pm

The cylinder I got is great for what I'm doing. The main problem is that it scratches easily--I'm eventually going to do something like coat it in epoxy or make a felt sleeve. The scratches are purely cosmetic so this is not a major problem.

My cylinder is #2636 as shown here: http://www.catalinacylinders.com/lp.html

Catalina Cylinders makes a bushing called the "F1" that goes from their unusual 1 inch thread to 1/4 inch NPT, but that's not very large. They might have bushings that go larger, but the cylinders listed online are limited to about a 3/4 inch ID.

I'd suggest calling them and asking about even larger sizes. The most helpful person I spoke to was named Joe Wolff, so ask for him if you're not getting good answers. Their capabilities are definitely not limited to what's shown online and I would not be surprised if they had something much like or exactly like what you want. I'd suggest being very upfront about what you're going to do with the cylinder. They're used to companies calling in but they'd love to help someone out with an odd project too, provided you don't beat around the bush.

I will not discuss what I paid out of kindness to Catalina Cylinders (they don't usually sell single units from what I can tell so I was an exception) but I will say that the cylinder I have (2636) costs $23.01 and the F1 bushing costs $8.42 for 25 to 200 units as of a few months ago. Again, call them and ask about single units.

Edit: One thing to note for others looking into using LPA cylinders from Catalina, realize that the pressure rating listed is a burst pressure, not a maximum operating pressure. Typically a safety factor of 2.5 over the burst pressure is used, so the maximum operating pressure is 240 psi for the 600 psi cylinders.
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Last edited by btrettel on Wed Mar 11, 2009 5:30 pm, edited 3 times in total.
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Unread postAuthor: daberno123 » Wed Mar 11, 2009 5:21 pm

Alright thanks for the info I'll make sure to call them when I start the project.
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Unread postAuthor: btrettel » Sat Mar 14, 2009 9:52 pm

Today I put together a few parts quickly for some testing. The gun works great as is, but the parts were put together just to see what dimensions are necessary. A wooden handle and different polycarbonate pieces will be used to hold everything together. The turret pieces aren't shown here either.

There's obviously still a good deal of work to do and I might need to remake a part made with FDM due to some warping, but aside from that problem everything's going great. I should have the gun completed within the next two weeks unless I have to remake that part with FDM.

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