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Audacity 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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Audacity file

Unread postAuthor: tghhs » Sat Oct 10, 2009 12:54 am

Hey everyone, so i've done the hard work and all.

At 140 psi with this gun: http://www.spudfiles.com/forums/coxial- ... 19362.html
Distance between muzzle and target 40 metres.
Distance between muzzle and mic 40 metres; had an argument with dad about this one, he was sure i had to have mic at target instead of centre. I thought the sound has to travel the same distance anyway so doesn't matter.

I worked it out to abe about 720 ft/s but this seemed way to high.

http://rapidshare.com/files/290998106/g ... .flac.html
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Unread postAuthor: Technician1002 » Sat Oct 10, 2009 1:05 am

If the bullet travels at the speed of sound the bullet and the sound from the muzzle will arrive at the same time for a 40 meter travel time of 0.0. It would appear to travel close to the speed of light. You dad is wrong.

You can compensate for the offset by adding the time of the sound to travel from the muzzle to the total so in the above example the time will not be 0.0 but the time sound travels 40 meters.

In the case of the projectile traveling at the speed of sound, the sound and projectile would take 0.116618 seconds, but the sound and projectile would arrive at the same time.
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Last edited by Technician1002 on Sun Oct 11, 2009 12:08 am, edited 1 time in total.
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Unread postAuthor: tghhs » Sat Oct 10, 2009 1:59 am

yeh techinician that makes sence. Anyway i recorded it again with Mic centre.

First recording:

Second recording:
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Attachments
gunshot4.rar
40m 140psi mic at target
(36.89 KiB) Downloaded 28 times
gunshot5.rar
40m 140 psi mic centre
(19.54 KiB) Downloaded 32 times
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Unread postAuthor: Technician1002 » Sat Oct 10, 2009 11:39 am

Very nice. I took the liberty of grabbing screen shots of the waveforms with a little zoom in on the area of interest.

Speed of sound is 343 meters per second. If you add the travel time for the sound to arrive from the muzzle to the time audacity gives you and compare results with the second shot, you will see the average flight time of both shots.

Link to source of the speed of sound reference;
http://en.wikipedia.org/wiki/Speed_of_sound
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gunshot4
Screenshot-gunshot5.jpg
gunshot5
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Unread postAuthor: boyntonstu » Sat Oct 10, 2009 11:55 am

tghhs wrote:yeh techinician that makes sence. Anyway i recorded it again with Mic centre.

First recording:

Second recording:


I calculate 717 fps/

Very good.

Muzzle velocity is higher of course

Projectile weight, etc?
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Unread postAuthor: Technician1002 » Sat Oct 10, 2009 2:00 pm

In the first example, sound has to travel from the muzzle to the mic. Sound at 343 meter/sec travels 1 meter / 0.002915452 seconds. In 40 meters the sound takes 0.116618 seconds to arrive.

First shot, sounds arrive at 0.561 and 0.742 seconds. The difference in time is 0.181 seconds. Add in the muzzle sound travel time of 0.1166 and you get a travel time of 0.2976 seconds. The muzzle blast happens before you hear it so the sound travel time must be added to the measured travel time.

In the second shot the travel time from the muzzle and the travel time from the target are the same, so we observe both arriving late by the same amount.

The muzzle blast arrives at 0.2464 seconds and the target impact arrives at 0.5440 for a travel time of 0.2976

I am impressed with the repeatability of the shots. Repeatable to 3 significant digits. I'm very impressed. This repeatability is one of the reasons I recommended an air cannon with accurate pressure control for the golfball engineering challenge by the way. Repeatability is very good with the cannon. With other parameters under tight control it could do well at hitting the targets.

Average flight velocity is based by distance divided by time. 40 meters divided by 0.2976 gives an impressive 134.4 meters / second.

I'm getting about 441 feet/second by visiting an online calculator. Did I make an error in my math somewhere?

@boyntonstu, please show your math. We can't both be right.

For an average speed for 40 meters this is still very impressive. Well done. As stated already, muzzle velocity is higher, much higher. :wav:
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Unread postAuthor: boyntonstu » Sat Oct 10, 2009 3:27 pm

Technician1002 wrote:In the first example, sound has to travel from the muzzle to the mic. Sound at 343 meter/sec travels 1 meter / 0.002915452 seconds. In 40 meters the sound takes 0.116618 seconds to arrive.

First shot, sounds arrive at 0.561 and 0.742 seconds. The difference in time is 0.181 seconds. Add in the muzzle sound travel time of 0.1166 and you get a travel time of 0.2976 seconds. The muzzle blast happens before you hear it so the sound travel time must be added to the measured travel time.

In the second shot the travel time from the muzzle and the travel time from the target are the same, so we observe both arriving late by the same amount.

The muzzle blast arrives at 0.2464 seconds and the target impact arrives at 0.5440 for a travel time of 0.2976

I am impressed with the repeatability of the shots. Repeatable to 3 significant digits. I'm very impressed. This repeatability is one of the reasons I recommended an air cannon with accurate pressure control for the golfball engineering challenge by the way. Repeatability is very good with the cannon. With other parameters under tight control it could do well at hitting the targets.

Average flight velocity is based by distance divided by time. 40 meters divided by 0.2976 gives an impressive 134.4 meters / second.

I'm getting about 441 feet/second by visiting an online calculator. Did I make an error in my math somewhere?

@boyntonstu, please show your math. We can't both be right.

For an average speed for 40 meters this is still very impressive. Well done. As stated already, muzzle velocity is higher, much higher. :wav:


"Anyway i recorded it again with Mic centre."

40
.181 ÷
--------------------------
220.994475138121547 =

39.37 ×
--------------------------
8,700.55248618784531 =

12 ÷
--------------------------
725.046040515653776 =
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Unread postAuthor: Ragnarok » Sat Oct 10, 2009 3:39 pm

boyntonstu wrote: "Anyway i recorded it again with Mic centre."

But you're using the file from when he didn't have it centre.

~0.18 secs is the time in the first file, with the mic near the target.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: boyntonstu » Sat Oct 10, 2009 3:42 pm

Ragnarok wrote:
boyntonstu wrote: "Anyway i recorded it again with Mic centre."

But you're using the file from when he didn't have it centre.

~0.18 secs is the time in the first file, with the mic near the target.


yeh techinician that makes sence. Anyway i recorded it again with Mic centre.

First recording:

Second recording:

followed by:

Very nice. I took the liberty of grabbing screen shots of the waveforms with a little zoom in on the area of interest.


I am confused?(>?
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Unread postAuthor: Ragnarok » Sat Oct 10, 2009 3:48 pm

boyntonstu wrote:I am confused?

The first recording is the original one, done with the mic next to the target.

The second one is the redone one.
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Unread postAuthor: boyntonstu » Sat Oct 10, 2009 3:55 pm

Ragnarok wrote:
boyntonstu wrote:I am confused?

The first recording is the original one, done with the mic next to the target.

The second one is the redone one.


English: First period.

Mathematics: Second period.

It feels like high school.

Thanks,

BoyntonStu

BTW How do you make nail darts? (Third period)
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Unread postAuthor: tghhs » Sat Oct 10, 2009 11:31 pm

Wow thanks guys, heaps of help.

here's some pictures of ammo and all:

Sorry I don't have any scales so i can't tell you how much it weights. :(
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Attachments
Ammo.JPG
Ammo: Golf tee sanded to fit in 1/4 barrel
Ammo.JPG (14.32 KiB) Viewed 636 times
piston and barrel.JPG
Teflon piston & Barrel, chamber background
piston and barrel.JPG (20.99 KiB) Viewed 636 times
piston in chamber.JPG
Piston in chamber; to show fit
piston in chamber.JPG (22.19 KiB) Viewed 636 times
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