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New wadding design and piston update - Also .wav file

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: boyntonstu » Fri Oct 23, 2009 12:48 pm

bump: Hoping for analysis of the last .wav file.
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Unread postAuthor: Technician1002 » Fri Oct 23, 2009 2:17 pm

boyntonstu wrote:bump: Hoping for analysis of the last .wav file.


Wow, 3 downloads and no comments on the file.

Before the trigger there is a low frequency sound which the trigger event (hiss) rides on. The trigger starts at 0.130. At 0.150 there is a sudden increase in the hum, indicating the original valve vibration is back, but it lasts a cycle and a half with a valve burp at0 01670 seconds followed by one at 0.1690. I call these burps as the amplitude is way too quiet. The valve is still trying to open but the o rings appear to be sticking so it re-seats as some chamber pressure drops.

We finally get a full amplitude pressure swing that oscillates into a clipped square wave beginning at 0.730. Again the record level is way too high so the impact is showing up only as a change in the frequency of the noise. This change appears at 0.230 for a possible flight time of 0.500 seconds. It is really hard to be sure on this one. Is there a way to turn down the record volume a lot? The waveform clipping is making this difficult. A square wave is difficult to detect volume peaks due to an impact.

I will give credit to those who tried. It's not an easy waveform to measure.
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Attachments
Hissboom.jpg
Sample of a useful recording with little clipping.
Good recording example.jpg
Textbook example of a cannon recording with the correct levels. There is no clipping. Amplitude is easy to compare over time. This is the 2 inch QDV with no projectile.
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Unread postAuthor: boyntonstu » Fri Oct 23, 2009 4:35 pm

Technician1002 wrote:
boyntonstu wrote:bump: Hoping for analysis of the last .wav file.


Wow, 3 downloads and no comments on the file.

Before the trigger there is a low frequency sound which the trigger event (hiss) rides on. The trigger starts at 0.130. At 0.150 there is a sudden increase in the hum, indicating the original valve vibration is back, but it lasts a cycle and a half with a valve burp at0 01670 seconds followed by one at 0.1690. I call these burps as the amplitude is way too quiet. The valve is still trying to open but the o rings appear to be sticking so it re-seats as some chamber pressure drops.

We finally get a full amplitude pressure swing that oscillates into a clipped square wave beginning at 0.730. Again the record level is way too high so the impact is showing up only as a change in the frequency of the noise. This change appears at 0.230 for a possible flight time of 0.500 seconds. It is really hard to be sure on this one. Is there a way to turn down the record volume a lot? The waveform clipping is making this difficult. A square wave is difficult to detect volume peaks due to an impact.

I will give credit to those who tried. It's not an easy waveform to measure.


First, thank you.

Sorry about the clipping.

I am almost positive that the valve vibration is due to slow opening of the valve.

However, this shot was VERY powerful nevertheless.

Not only did the marble make a hole an go through the 5/8 plywood, it went about halfway into a 3/8 plywood sheet located behind the 5/8.

I will quiet down the mic some more and make an unclipped .wav.


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