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power comparisons

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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Which one do you think will do the best?

"American Style" QEV
1
50%
"European Style" QEV
1
50%
 
Total votes : 2
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power comparisons

Unread postAuthor: Lockednloaded » Tue Jan 04, 2011 7:33 pm

I have always wondered if different brands of valves we use yield better performance, but pretty soon, I'll be able to test it.

I have a 3/4" detrol "american style" QEV from mcmaster-carr, and I will be getting a 3/4" "european style" QEV shortly. While I'm comparing these two, I'd also like to try my own homemade 3/4" barrel sealing tee valve, and even maybe a 3/4" or 1" sprinkler valve.

Because I don't have a chronograph or sound equipment, I will not be measuring velocity. I will not be taking damage shots either, so in order to compare all of these fairly, they will all use the same chamber, same pilot valve, and same pressure, but in order to be able to measure distance the projectile travels, I will be using a horribly inefficient large bore barrel.

Do you think such a setup will be accurate to determine which valve is best?

Should I try a sprinkler valve as well?
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Unread postAuthor: Technician1002 » Tue Jan 04, 2011 7:52 pm

A large bore barrel with a lightweight projectile can give a good indication of how well a valve flows. I used a 4 inch barrel with a foam ball to test the flow of my 2 inch valve. I used a home made magnetic chrony to measure the in barrel acceleration.

Details of several home built chrony projects are in the Wiki. Thanks JSR for adding this.
http://www.spudfiles.com/spud_wiki/index.php?title=Chronograph

Because I don't have a chronograph or sound equipment, I will not be measuring velocity.

A magnetic one is easy to build and very accurate without requiring exotic materials. A laptop with a sound card works fine.
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Unread postAuthor: Lockednloaded » Tue Jan 04, 2011 8:15 pm

As far as a laptop goes, I have a MacBook.

And a little more detail on the homemade valve, It 1/2" porting (the seat is a 1/2" nipple)
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Unread postAuthor: Technician1002 » Tue Jan 04, 2011 10:29 pm

Does the MacBook have a MIC or Line input?

I presume if it supports VOIP, it has to have some kind of sound input.

If not, a normal USB headset or other external USB sound module should work fine for an input device.

Get the sound recording software here for free;
http://audacity.sourceforge.net/download/mac
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Unread postAuthor: Lockednloaded » Tue Jan 04, 2011 10:44 pm

so basically I just turn on the mic, record the shot, and then I can calculate the FPS?

Its weird a lot of you voted homemade, I didn't think it would turn out that way. Voice your opinions on why you think it'll be better please
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 05, 2011 1:04 am

I don't think the difference will be perceptible enough to determine without some sort of chrony. I had done some limited testingwith the microphone/audacity method and found it to be quite accurate in the single comparison with a commercial chrony that I made.

And a little more detail on the homemade valve, It 1/2" porting (the seat is a 1/2" nipple)


That skews the results significantly, as commercial 3/4" valves may have greater than 3/4" porting.

Technician1002 wrote:Thanks JSR for adding this.


JSR is a little ticked off he was sans internet for the seasonal holidays as he was expecting to get a lot of work done on the wiki :s
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Unread postAuthor: Technician1002 » Wed Jan 05, 2011 1:39 am

Lockednloaded wrote:so basically I just turn on the mic, record the shot, and then I can calculate the FPS?


You can use a microphone or wire a plastic barrel to detect a passing magnet. I found the passing magnet to be very accurate.

The inverse of delta time between pick up coils is speed. For example 1ms to cross two points a foot apart when inverted becomes;
1ms = 1/1,000 seconds = 1,000 FPS.
Using Audacity you can find the times of each coil crossing.
Image

You can zoom in for fine detail on a pair of crossings.
Image

Subtracting the start time from the end time will give the delta time as shown in this photo. As shown the first coil is at 0.379 seconds and the second is at 0.412 seconds. The travel time is 0.033 seconds. If the coils are a foot apart that inversion 1/X comes to about 30.3 feet/sec.

This test recording was made with a dropped magnet and the coils closer than 1 foot, so the projectile is slower than the above calculation. Zero crossing on the S curve is the magnet going through the exact center of the pick up coil as it is neither approaching or departing from the coil.

The increase in amplitude and decreasing times between crossings is due to acceleration due to gravity.

If you are a physics major, you can use acceleration due to gravity to calculate the distance between my coils in the test recording and the height of the projectile when it was dropped. Bonus points for correct answers.

I didn't think it would turn out that way. Voice your opinions on why you think it'll be better please


1 Magnetic is Immune from muzzle blast fog typical of air cannons.
2 In barrel acceleration can be measured.
See this page for details. It details the advantages and disadvantages of each.
http://www.spudfiles.com/spud_wiki/index.php?title=Chronograph

Using a scope instead of a PC and Audacity, here is a real shot from my air cannon. The projectile is a 4 inch foam ball. The coils on the barrel are 1 foot apart. Horizontal time base is 2.5 ms per major division. Measurement result for the crossing of the last two coils is displayed on the right. Time to go 1 foot is 2.200 ms.
Image

Trust me.. You would not want to get hit with that foam ball at close range.
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