jonnyboy wrote:Thanks for clearing that up. I thought you just drilled a couple holes in the pipe.
While we're talking about hotwireds sig its to make noise.
I have photos of the ports on
http://inteltrailblazerschallenge.wikis ... +brag+zone
Look down the page to the pipe for the 2 inch valve with the rectangular holes in it. In the marshmallow cannon, I put them even closer to the end of the pipe. The edge of the holes is only 1/4 inch from the base of the threads. This was designed for maximum airflow, and little restriction.
What is the use of pressure in the chamber after the projectile has left?
As far as the pressure remaining in the tank, with a long barrel and low pressure, I can run the pressure negative. On this page
http://inteltrailblazerschallenge.wikis ... rim+method
I have some in barrel acceleration graphs. Shown is a low pressure shot where the projectile accelerated, peaked, and then decelerated to about 1/2 the initial speed as it drew below 1 atm in the tank.
This happens when the volume in the tank at the operating pressure is less than enough to fill the volume of the barrel and projectile inertia is enough to carry it out anyway.
Shots with just enough pressure to fill the volume of the barrel are silent for truly stealth shots. A small chamber at a higher pressure can be very efficient with the air supply in this regard. Most people want the FPS, so they go larger on the chamber to keep the pressure up in the barrel during the shot.
882 fps with an apple at only 80 psi? that is so awesome!!!!!! I get it you could make a 1/4" coaxial one that would propel steel BB's at high speed too?
Why not? Remember as the area decreases in the smaller diameters, the force drops. Friction becomes a serious enemy. Look for future posts on some design consideration for very low friction o ring use.
The simple soulution is to simply unscrew the 1.25 inch barrel and screw on a 0.25 barrel adapted to a 1 inch pipe fitting and start shooting.
I learned a lot in using o rings. Some learnings appear to be dead wrong at first glance, but that is for a later discussion.
Due to the thin metal of the disposable tank, we were hesitant at running at high pressure until we got a full hydrostatic test completed. That is why the apple was launched at only 80 PSI in the large cannon. After the higher pressure fruit launches, we felt safe to use the shirt launcher at 50 PSI and below.
At 20 PSI, I can hit the roof of the Rose Garden Arena with the long 3 inch barrel and a rolled up t shirt.
If you where to connect a piston at the back, wich gets pushed back by the outgoing pressure,closing the valve rapidly, you've got all the benefits, yet multishot capability.
Speed is the issue, especially on smaller volume chambers. I haven't done the discharge time on the little tank yet, but the large 700 cu in tank completely empties in only 14 ms. Getting something to cycle the piston that fast without breaking the reset pin would be difficult as the acceleration forces would be insane. I suspect the little tank is able to completely empty in well under 10 ms. I'll do some pressure discharge graphing later to find out.
For multi shot, I have toyed with a way to make it work. After testing, I'll possibly start a thread on one.
There are 2 ways to test the discharge time of your valve cannon. 1 is high speed photography. Look at the fog, smoke, or mist in this sequence;
https://inteltrailblazerschallenge.wiki ... com/Photos
The start of the flow is indicated by the label on the bottle waving in the breeze and the end when the flow stops. The other way is to use a high speed transducer. A very light piston in an air collum can be photo or magnetically detected as a fast pressure gage.
***EDIT The O Ring thread is started and the associated video shows the valve opening force***
http://www.spudfiles.com/forums/viewtop ... tml#239004
