Labtecpowers (soon-to-be) quick dump valve cannon

Labtecpower · Sat Feb 19, 2011 12:43 pm

It is very awkward to hold now. I'm going to make a shoulder strap, and the "chainsaw" handle JSR showed me

.....and indeed, a hat and sunglasses would have been easier

nature-boy · Sat Feb 19, 2011 12:57 pm

Good Job!
In the video it looks like you needed at least two tries to actuate the valve.
Or does it only looks like that?
And it also looked like your barrel flexed...

...and I didn't really needed a sign to the place where your face is located at your body.
...but at some people it would perhaps be helpful...

Technician1002 · Sat Feb 19, 2011 1:20 pm

If he is like me, it is nice to see how much free travel the rod has before it hits the piston. I sometimes do the same thing so I know where in the stroke it will pull the piston. The trial strokes were not meant to pull the piston.

Think of how you shoot pool. Do you move the cue stick before taking the shot?

nature-boy · Sat Feb 19, 2011 1:28 pm

@Tech
yeah I thought of that but I wasn't sure.
How hard is it to pull the rod in QDV's?
Do you really have to slam it against the piston, or would it be possible to just pull onto the piston, with a rope for example?

Labtecpower · Sat Feb 19, 2011 1:34 pm

I was indeed trying to see how much travel the rod has

It is very simple to open. A gentle pull is enough.
The recoil isn't too bad . I expected it to be much more.

I'm contacting a mod to move this topic to the "pneumatic cannon showcase" area.

Technician1002 · Sat Feb 19, 2011 1:36 pm

nature-boy wrote:@Tech
yeah I thought of that but I wasn't sure.
How hard is it to pull the rod in QDV's?
Do you really have to slam it against the piston, or would it be possible to just pull onto the piston, with a rope for example?

The higher the pressure, the tighter the o rings set. Pulling force varies. Rope pull is not difficult. The ABS cannon in my sig is a rope pull. The o ring video shows the cannon opening the valve at no pressure just by shaking it. At high pressure the impact helps dislodge the piston and get it up to speed early in the pull. The rod decoupled from the piston moves freely.

The cannons with floating rings can be shaken open when not under pressure. My Youtube channel has several videos showing the pulling of several cannons. One is a preschooler pulling the Marshmallow Cannon at 100 PSI. Another one with a 100 PSI soda launch with the 2 inch shows a friend of mine having to give a couple tugs to fire it as he was too gentle. It did not fire on the first pull.
Check my uploads in my youtube channel.
http://www.youtube.com/user/Technician1002

One of the reasons I am building a 2.5 inch before building a 3 or 4 inch is to see how much the force increases. I may need to pilot a 3 or 4 inch cannon. The other reason is to work on some bumper designs. Bigger cannons will need something to prevent piston rebound.

Videos;
http://www.youtube.com/user/Technician1 ... usGJKJ4EL0
preschooler pulling at 100 PSI.

http://www.youtube.com/user/Technician1 ... bDiZiRVrnk
Shaking a valve open. Fast forward to 5 minutes.

http://www.youtube.com/user/Technician1 ... MzvW1Fy34E
100 PSI shot with a missfire. I tell him "Pull it hard"

Labtecpower · Sat Feb 19, 2011 4:23 pm

The barrel flexed quite badly. I will take care of that I think.

And about the piston rebound; have you ever tried to make vent holes in the pilot area of your valves?
I think the rebound is because of air that can't get away fast enough, and pushing the piston back in place.

Also, a less springy bumper material could be used. The knee pads tend to be very bouncy. I was thinking of using Tempur-foam or something in that direction, as it absorbs shocks very well, and takes al while to recover it's shape.

Technician1002 · Sat Feb 19, 2011 6:06 pm

I am working on a multi layer mass and energy absorbing pancake that will work like a very high loss newton's cradle. Much like the first ball stops with the impact, the piston will stop on impact, then the subsequent layers will all absorb kinetic energy. It is planned for the 2.5 inch I am very slowly building.

Think of one of these with a squishy rubber/sand pack between the balls so the rebound never returns.
http://www.youtube.com/watch?v=sLZV0Y-VtGw

Labtecpower · Sun Feb 20, 2011 1:48 pm

I did some test shooting today. I went up to 6 bars, and the recoil wasn't too bad. I'm definately going for 10 bars!

I was shooting with a friend, so there where two people to absorb the shock.
(I was holding the barrel tightly, and aiming, and my friend pulled the rod)

The power this thing has, is very nice. I was able to shoot through a 3/4" inch plywood, wich is VERY tough. I shot it with my copper gun at 16 bars, and it just left a dent

[youtube][/youtube]

I hope you like it

Technician1002 · Mon Feb 21, 2011 6:24 pm

Labtecpower wrote:also, i'm a bit worried about deformation of the valve pipe. I also want to cool it on the inside, to prevent the zinc coating to vaporize. Do you have any experience with this? I was thinking about putting a wet ball of toilet paper in the pipe.

The weld will be MIG/MAG.

Bump to update. Located an earlier construction photo showing the lack of distortion on the 2 inch valve after brazing. It shows the burnt zinc from the brazing. This did not take too long to sand down to the smooth bare iron shown in the finished valve photos.

Labtecpower · Tue Feb 22, 2011 4:18 am

There was very little distortion in my gun, and just a little zinc burnt away.
The zinc oxide was easily removed, and the inside of the pipe stayed really smooth.

I'm going to make a detachable barrel support, with a nice handle.
It will be a bit like the designs I showed.

I can work on it in about a few weeks, as I have some more important stuff to do, and I don't have access to any cutting / welding equipment right now.
I want to do all the cuts on a band saw, to make sure they are perfectly straight.
In that way I can TIG- weld them without adding any metal.

I tried a few 100 psi shots. I was very impressed

I'm going to make some concrete ammo now, out of some toilet paper rolls.
I have the feeling that heavy ammo is giving me the most range.

Technician1002 · Tue Feb 22, 2011 6:20 am

I would recommend removing the ring from the tank before shooting them. It could leave a mark.

I said you would be impressed at 100 PSI..

If you have heavy ammo and a large diameter barrel, the recoil can be brutal.

Do you have a 2.5 or 3 inch barrel yet? Try to make a soda can / tennis ball barrel for it. It is my favorite size. It is one of the reasons for the 2.5 inch build.. The valve will match the flow needs of the barel for maximum effeciency.

Labtecpower · Tue Feb 22, 2011 6:33 am

I think i'm going to get a larger barrel.
Is the flow enough for some good performance?

I haven't been hurt enough by the ring to remove it now. I'll do it in a while

When I finished the grip and the shoulder sling, my hip won't take the recoil.
I'll have to pay attention that the barel support will fit the 3" barrel.

Technician1002 · Tue Feb 22, 2011 6:59 am

As you go larger, the limitations of the flow does start to become a problem, but in the cross over between the larger cross section and flow, several sizes of barrels larger than the valve still have very impressive performance. On my 2 inch valve, the 4 inch barrel does OK as well as the short 2.5 inch barrel on the 1 inch valve. Launching full soda cans ( or empties ) from the tube is very impressive. Max recoil was achieved launching a Gatoraid from the 3 inch barrel on the 2 inch valve.

In short the performance is still quite impressive when using barrels up to 1.5 times the valve size.

Using the 4 inch barrel and a light foam ball was still enough to bust the bottom out of a 5 gallon poly bucket.

Here is a selection of barrels larger than 2 inch I use on that cannon.

I almost never use the 2 inch barrel. Most of the time I use the 2.5 inch or 3 inch.

Here is my raw data of a 4 inch foam ball launched from the barrel. At only 60 PSI, it was near 500 FPS.

Info on how that scope print was produced, this page explains it. In the photo of the barrels, the 2.5 PVC and 3 inch ABS barrels currently has the pick up coils taped on it at 1 foot spacing.
https://inteltrailblazerschallenge.wiki ... rim+method

Labtecpower · Tue Feb 22, 2011 2:17 pm

I think i'm going to buy a tennis ball / soda can barrel in a while.

I want to measure the speed of my bullets. I tought of a setup like this;

Would this be more accurate than measuring by a muzzle blast, and the projectile hitting a target?

If I have the chance, I would love to build a 4 inch QDV cannon.
I will first search for O-rings, as they are harder to find than a pipe of the right diameter. I think that a 4-inch cannon needs a shock absorbing system.