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Presenting The Mouse Musket

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Presenting The Mouse Musket

Unread postAuthor: Technician1002 » Mon May 31, 2010 12:37 pm

I refer to The Mouse Musket often to help describe construction ideas and piston theory. I had a request to post this so here it is in all it's glory.

Image

The musket started as a concept before I joined SF as about my 4th piston cannon. This was up to that date my most advanced cannon. Since engineering is a hobby as well as a job, I looked at my past failures and looked to improve upon them. This is the result.

One of my old designs had a long piston, drilled holes for porting, and a dual diameter piston ( like a barrel sealer QDV ). The piston stuck, was slow, and if it worked flowed poorly. This is a successor to an earlier failure the Light Saber. A couple of SF members have been unfortunate enough to have seen it and it's super long piston.

For the design I wanted a compact cannon that would be easy to fill with a bike pump (before I got a compressor), flow very well, have a fast piston etc.

This meant a piston design. Due to the complexity of 2 o rings on the last cannon it was decided to try a build with no o rings on the piston. The goal was a very fast piston. Lightweight was part of the solution. The other part was a close piston ratio. A large seat and small outside diameter on the piston provided a close ratio piston. I did not have a drill press at this time. This build was completed with hand tools.

For the specifications;
The piston OD is 1.5 inch.
The valve seat is 1.25 inch.
The chamber is 2 inch PVC.
The barrel is 1 inch PVC
All PVC is schedule 40.

To keep the weight down on the piston, it was decided to attempt to move the weight of the barrel seal off the piston and move it to the end of the barrel. In doing so, the diameter of the valve seat became larger in diameter to make the piston ratio even closer to a 1:1 ratio.

To make the OD of the piston smaller in diameter, the piston was fitted inside a smaller piece of pipe. To reduce parts count and make it unique an unusual construction trick was done. I placed a 1.5 inch female adapter inside the 2 inch chamber by heating the chamber and shoving it in stretching the chamber larger to fit. The female adapter has a very short piece of 1.5 inch pipe inside it to become the piston cylinder.

The valve seat was created by hand with a small round file. I filed a groove around the outside of the barrel when it was much longer. This groove fit an o ring on the outside of the barrel. A ring was cut off a 1 inch pipe coupler and one end was carved out to fit over the o ring. The o ring was removed and the coupler was glued in place. Using the end of the coupler as a guide, the barrel was cut leaving this space for the o ring. the gap got a little bathroom caulk and the o ring was squished into the caulk. The barrel was stood on end and balanced to set the o ring in the glue true and flat.

To make a spacer to center the barrel. 3 short pieces of poly tubing was used. They were drilled sideways through the middle and these three pieces of tubing was zip tied to the barrel about 6 inches from the breech. The tubing squeezed down slightly to fit in the chamber and centered the barrel perfectly.

This launcher fit 1 inch gumballs and almost became the gumball gun. One day I killed a mouse (I hope I don't get banned for this) in a mousetrap. In disposing of it outside, I noticed it was about the right size. The mouse went over the back fence into the field beyond. The name stuck ever since. It has never been used to launch a live animal.

In testing to see if it met the design goals, a fast valve would be needed with good flow to get high speeds on light projectiles in the short barrel. I didn't have a chronograph. I decided to splat a gumball on a sheet of plywood to see if it would dent it. To my amazement, it punched a hole right through it.

The cannon was hard on valves. It broke 3 pistons. 2 broke in the center of the face of the piston. The 3rd broke on the side next to the eq hole. The 4th piston was made from HDPE. It didn't break. Unfortunately, the Musket got dropped and developed a crack in the front coupling. I retired it due to the leak and donated it to the Arlington HS science department.

Piston showing the small eq port and the crack that failed the last pipe cap valve. Most piston failures were a hole broken in the very center of the face of the piston. This is a spot not hit by anything. It is PVC fatigue that caused the failures. The hole was drilled with a printed circuit drill bit. It is tiny.
Image

The PVC failures in this cannon was the direct inspiration to test alternate materials. This is the reason the ABS Cellular Core Test Cannon was built.

Edit; Added detail drawing of the barrel seal. The void behind the o ring is filled with caulk.
Image
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Attachments
The Musket.JPG
Presenting The Mouse Musket
The Musket Muzzle.JPG
The muzzle showing the unusual use of a reducer
The Musket Breech.JPG
The Musket Breech showing the 1.5 inch female adapter inside the 2 inch chamber
The breech piston.JPG
This shows the original PVC 1 inch pipe cap as a piston inside the 1.5 inch inner cylinder in the female adapter.
The breech seat and piston.JPG
With the piston out you can see the valve seat.
The piston was gently sanded on a piece of sandpaper glued to the plywood until it just fit inside the breech. Note the sanded appearance.
The Breech open.JPG
A 1.5 inch pipe plug with a hole for either a blowgun or 1/4 inch ball valve finished the cannon. Note the hole in the plywood. This is a gumball hole. The o ring seal area on the piston face can be seen.
Gumball hole.jpg
This is the exit side of the hole.
Gumball hole.jpg (37.4 KiB) Viewed 3247 times
The Musket1.JPG
A decent shot of the Musket artwork finishes this series of photos. This cannon lasted 5 years. It broke almost a piston per year. The sandpaper glued to the board is the piston size adjustment tool. ;-)
Musket Crack.JPG
All good things must come to an end. This got knocked over and cracked the coupler. The crack spread inside to the chamber wall and reducer inside. The reducer crack leaked. The leak was discovered before it blew up.
80PSI.zip
The musket sound at 80 PSI. A gentle blowgun squeeze shows the valve pops even with a slow pilot. This is a dry fire indoors. This is the original PVC piston. A close ratio valve does not honk or go put put put. It pops open and remains open.
(4.01 KiB) Downloaded 162 times
musket breech.JPG
Musket breech detail. Female adapter with 1.5 inch pipe is added in the 2 inch chamber. The o ring becomes part of the valve seat.
Last edited by Technician1002 on Thu May 26, 2011 10:57 pm, edited 21 times in total.
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Unread postAuthor: Zoltar9879 » Mon May 31, 2010 12:52 pm

Very Nice launcher! 8) I Like the name and artwork, and all of the thought that obviously went into this. Great job :D
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Unread postAuthor: deathbyDWV » Mon May 31, 2010 12:57 pm

This makes me want to build one similar... :D
I really like how simple it looks on the outside...
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The updated piston photos.

Unread postAuthor: Technician1002 » Tue Jun 01, 2010 1:18 am

It is only fair to move the making of a replacement piston here. This series of photos should be fairly self explanatory.

Image
This photo shows the piston ratio very clearly. The area inside the seal is large. The perimeter outside is very narrow. New material is 3/4 inch sheet HDPE

Image
A manageable size piece is cut to become a piston.

Image
The hole is for a bolt so it can be attached to the drill press. The hole is only 1/2 the way through.

Image
The wood chisel is clamped solid and the piston is lowered past it to machine it. This is repeated in small steps until the piston is just small enough to fit.

Image
The bumpy surface is machined off the face for a good seal. The chisel is passed under the piston to make this radial cut.

Image
A small EQ port is drilled from the chamber area to the pilot area.

Image
Done. It fits like a glove.

I do hope to see some better pistons posted on Spudfiles. 8)
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Last edited by Technician1002 on Mon Aug 30, 2010 7:32 pm, edited 4 times in total.
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Unread postAuthor: Gun Freak » Tue Jun 01, 2010 8:01 pm

That's a nice explanation, too bad I don't have a drill press though :?
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Unread postAuthor: Technician1002 » Tue Jun 01, 2010 11:51 pm

Mine is the small one from Harbor Freight. It was on sale for $40.
Keep your eyes open for specials if you are on a budget.

That silly little drill press vise cost almost as much as the drill press. They nail you on extras.

The original Musket and PVC piston was built without any power tools. Even a hand drill was used.
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Last edited by Technician1002 on Wed Jun 02, 2010 12:16 am, edited 1 time in total.
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Unread postAuthor: Crna Legija » Wed Jun 02, 2010 12:12 am

i got a drill press at the market for 20 bucks, it was missing a belt tho.
luckily at work we have a machine the makes v belts, so i get that for free
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Unread postAuthor: jrrdw » Wed Jun 02, 2010 5:32 am

To the front of the line. 4
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