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| Antonio |
 Posted: 01/04/2008 19:23 PM Post subject: Homemade chronograph |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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This post will give u instructions to measure the speed of your projectiles shot:
Materials needed:
1. mp3 player with recorder (or mic on a computer)
2. audacity audiosoftware
http://audacity.sourceforge.net/latest/audacity-win/audacity-win-1.2.6 .exe
3. 'ruler'
4. metal target
Method:
1. Set the target at 26.2 ft
2. Start recording using ur mp3 or mic on the computer
3. Shoot the target
4. Put the audio file on your computer
5. Open audacity
6. Import audio (via button project)
7. Please look at the pictures I posted> further instructions there
Calculation:
Speed in ft/s = [8/(time taken-(0.02353))]*3.3
>>Speed = [Distance/(time-(distance/speed of sound))]*m/s to ft/s conversion
Thats it! Takes about 10 minutes first time>pictures should help. Plz post if you have questions or comments.
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875 Time(s) |
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773 Time(s) |
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Last edited by Antonio on 01/23/2008 11:38 AM; edited 1 time in total |
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| jackssmirkingrevenge |
| Posted: 01/04/2008 23:20 PM Post subject: |
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aspiring machinist
Joined: 15 Mar 2007
Posts: 18017
32416.86 Spud Bux
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| I'm curious to try this out to compare the accuracy to proper chronographs - my concern would be that for example in a pneumatic rifle, the first noise would be the sound of the hammer hitting the valve, not the pellet leaving the barrel.
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| BigGrib |
| Posted: 01/04/2008 23:33 PM Post subject: |
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GribNation Founder
Joined: 01 Oct 2007
Posts: 652
286.99 Spud Bux
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i have used cool edit pro 2.0 to do the same thing with my combustion and my pneumatic and if the end of your barrel is close enough you can see the changes in the audio dynamic and you can kind of pick out exactly where things happen. one thing i have a problem with about ant's way of doing it you lose audio quality not recording it on your computer. use an actual recording software like cool edit pro 2.0 which is now adobe audition although you can still get cool edit pro (i feel is better) from oldapps.com, instead of haveing to record and import and all that stuff.
the target i use is a 2 gallon steel pot at 50ft away cause even at 50 ft you can still pick up a good hit sound from that range. like i said i put my microphone at the end of my barrel and you will see a change in the audio dynamic when it is fired and when the projectile leaves the barrel and then when it hits your target.
Now this isn't 100% accurate as a regular chrono, but it will give you a pretty good estimate as to what your velocity is. i dont know poor man's chrono but if it works it works
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| Solar |
| Posted: 01/04/2008 23:49 PM Post subject: |
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Major
Joined: 17 May 2005
Posts: 390
1252.03 Spud Bux
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| Seems like it should work well. The humidity will change the speed of sound only slightly and everything else seems relative.
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| Antonio |
| Posted: 01/05/2008 4:50 AM Post subject: |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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| jackssmirkingrevenge wrote: | | I'm curious to try this out to compare the accuracy to proper chronographs - my concern would be that for example in a pneumatic rifle, the first noise would be the sound of the hammer hitting the valve, not the pellet leaving the barrel. |
Well yeah thats true. But using audacity you could take the highest peak I guess > when the projectile leaves the barrel. The problem with spudguns is that they have too much air. They have a long tssshhh after launching, this could interfere with the sound of the projectile hitting. This could be fixed by putting the recording device below the target. As I have a speed of sound time correction the mic must be put in line with the barrel (on the ground) or below the target.
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| Antonio |
| Posted: 01/05/2008 4:55 AM Post subject: |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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| BigGrib wrote: | i have used cool edit pro 2.0 to do the same thing with my combustion and my pneumatic and if the end of your barrel is close enough you can see the changes in the audio dynamic and you can kind of pick out exactly where things happen. one thing i have a problem with about ant's way of doing it you lose audio quality not recording it on your computer. use an actual recording software like cool edit pro 2.0 which is now adobe audition although you can still get cool edit pro (i feel is better) from oldapps.com, instead of haveing to record and import and all that stuff.
the target i use is a 2 gallon steel pot at 50ft away cause even at 50 ft you can still pick up a good hit sound from that range. like i said i put my microphone at the end of my barrel and you will see a change in the audio dynamic when it is fired and when the projectile leaves the barrel and then when it hits your target.
Now this isn't 100% accurate as a regular chrono, but it will give you a pretty good estimate as to what your velocity is. i dont know poor man's chrono but if it works it works |
Hey have u tried with using my speed of sound correction? subtract 340/distance from the time. (in meters)
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| jackssmirkingrevenge |
| Posted: 01/05/2008 4:56 AM Post subject: |
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aspiring machinist
Joined: 15 Mar 2007
Posts: 18017
32416.86 Spud Bux
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| I have one of these on order, not at all expensive new, even less from eBay, when it arrives and I have time might do some accuracy comparisons. The theory is sound, the difficulty is knowing which peaks to ignore.
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| Antonio |
| Posted: 01/05/2008 5:02 AM Post subject: |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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| Solar wrote: | | Seems like it should work well. The humidity will change the speed of sound only slightly and everything else seems relative. |
Yeah as u are saying the speed of sound does change a bit. But its a correcting factor so yeah, it already makes it more accurate. The problem with this method is that U dont take the downwards dwell into account which is caused by gravity. The projectile will always hit lower then the height of where it is shot at. This means it has a longer path. But if you leave out friction in the y direction (vertical) the vertical displacement of the projectile is: s=0.5*9.81*t^2 I am not sure how I can implement this as the path of the projectile is a parabol and not a straight line.
| BigGrib wrote: |
Now this isn't 100% accurate as a regular chrono, but it will give you a pretty good estimate as to what your velocity is. i dont know poor man's chrono but if it works it works |
Hey have u tried with using my speed of sound correction? subtract 340/distance from the time. (in meters)
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| BigGrib |
| Posted: 01/05/2008 5:03 AM Post subject: |
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GribNation Founder
Joined: 01 Oct 2007
Posts: 652
286.99 Spud Bux
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| i have been manipulating sound for quite a while, i mean i've been doing radio for over 10 years i can hear a pindrop from a mile away trough my headphones, and i have been listening to some of my recordings, slowing them down by the power of 10 and i can actually hear the difference in the sound right when the projectile leaves the barrel, there is a change in pitch, not too much but it is noticeable to the trained ear, that is with a pnuematic anyway. with a combustion it's a lot harder because of the bang, the projectile actually leaves the barrel before the bang is finished.
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| Antonio |
| Posted: 01/05/2008 5:11 AM Post subject: |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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| jackssmirkingrevenge wrote: | | I have one of these on order, not at all expensive new, even less from eBay, when it arrives and I have time might do some accuracy comparisons. The theory is sound, the difficulty is knowing which peaks to ignore. |
I am really curious to c the comparison. I have been using this for a while now and I have no way of checking.
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| Antonio |
| Posted: 01/05/2008 5:13 AM Post subject: |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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| BigGrib wrote: | | i have been manipulating sound for quite a while, i mean i've been doing radio for over 10 years i can hear a pindrop from a mile away trough my headphones, and i have been listening to some of my recordings, slowing them down by the power of 10 and i can actually hear the difference in the sound right when the projectile leaves the barrel, there is a change in pitch, not too much but it is noticeable to the trained ear, that is with a pnuematic anyway. with a combustion it's a lot harder because of the bang, the projectile actually leaves the barrel before the bang is finished. |
If you used AUDACITY the sound becomes visual like in the pictures I posted, this makes it easier to analyze to my oppinion. But yeah you sound like you have a very trained ear, respect. But what I am trying to say to all the other users is that for a pneumatic/bb gun u dont need a trained ear to get this right as everything can be done visually.
Sorry for multiple posts, I am just really keep talking to ppl about this topic.
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| jimmy101 |
| Posted: 01/05/2008 11:10 AM Post subject: |
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Lieutenant General
Joined: 28 Mar 2007
Posts: 2861
11955.58 Spud Bux
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You can of course directly record the sound in audacity, no need for the seperate recorder.
You should take a look at SoftChrono, which automates the process fairly well.
This forum also has some info on using sound (or a sound card in a PC) for a chonometer.
http://www.spudfiles.com/forums/viewtopic,p,38919.html#38919
http://www.spudfiles.com/forums/viewtopic,p,142566.html#142566
http://www.spudfiles.com/forums/viewtopic,p,122750.html#122750
http://www.spudfiles.com/forums/viewtopic,p,116408.html#116408
http://www.spudfiles.com/forums/viewtopic,p,111870.html#111870
http://www.spudfiles.com/forums/viewtopic,p,66086.html#66086
Your muzzle to target distance does not have to be so large, nor does it have to be 26.2 feet. All you need to know is the distance from the muzzle to the target. I would suggest a much shorter distance since the projectile is slowing down pretty quickly and this method (indeed all chono methods I can think of) give the average speed over the measured distance.
If the microphone is the same distance from the muzzle as it is from the target then you don't have to worry about the difference in time the sound takes to travel from the two sources to the mic.
You might take a look at the links above or my phototransistor DIY chono which is almost as simple as the mic setup but give a much more easily interpreted recording.
Here is a phototransistor/sound card recording of a BBMG firing. Each pair of peaks is a single BB.
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| jimmy101 |
| Posted: 01/05/2008 11:11 AM Post subject: |
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Lieutenant General
Joined: 28 Mar 2007
Posts: 2861
11955.58 Spud Bux
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BTW, if the mic is equidistant from the muzzle and target then the average velocity of the round is just;
v = (distance between muzzle and target)/(time between sound signals)
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| Antonio |
| Posted: 01/05/2008 12:31 PM Post subject: |
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Captain of Industry
Joined: 13 Aug 2006
Posts: 508
70.97 Spud Bux
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| jimmy101 wrote: | Your muzzle to target distance does not have to be so large, nor does it have to be 26.2 feet. All you need to know is the distance from the muzzle to the target. I would suggest a much shorter distance since the projectile is slowing down pretty quickly and this method (indeed all chono methods I can think of) give the average speed over the measured distance.
If the microphone is the same distance from the muzzle as it is from the target then you don't have to worry about the difference in time the sound takes to travel from the two sources to the mic.
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I chose 26.2 ft (8m) inorder to make it easier for ppl to calculate. I dont think all ppl here get what we are talking about, so I tried to make it as basic as possible. A larger distance means that u have less error. But ofcourse it wont give u the muzzle velocity rather the average as I said before.
About the distance thingy where the mic has to lay. Yeah I thought that over before as well. But I think it would be cooler and easier to put it on your gun, then u have to only measure the distance once. Also this is a very simple addition.
Thnx anyways for ur comments. Ill go ahead and try ur method of using this soft-chroning''
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| BigGrib |
| Posted: 01/05/2008 13:09 PM Post subject: |
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GribNation Founder
Joined: 01 Oct 2007
Posts: 652
286.99 Spud Bux
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@ ant cool edit pro shows you the waveform in a visual form but as jar said how would you know which peaks to ignore to find which one is the projectile leaving the barrel, which is where the trained ear comes in, but i mean you can guesstimante which one to use.
@jimmy if you put the mic equidistant from the barrel and the target you get an even response, but you dont get a very good sound from the barrel. solution...use a mic at the barrel and a mic at the target
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