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Homemade chronograph

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Unread postAuthor: Antonio » Sat Mar 01, 2008 9:23 am

jackssmirkingrevenge wrote:Wow, I only had time for 1 test but this is remarkably accurate! Of course I need to do more to validate it as a scientific method compared to a commercial chrony, but it looks very promising.

I shot a shotgun sabot at a metal plate 4 metres away, the chrony reading was 299.1 feet per second. I got two distinct peaks on audacity that were 0.06966 seconds apart, going by ant's calculation this gives a velocity of 286.1 feet per second. The chrony was 1 metre away from the muzzle, all in all I'd say it was pretty much spot on.

I had to back down on the pressure for relatively low velocity in order to get two discernable peaks, so for high velocity projectiles you'll need a significant distance to the target in order to get usable results, a laptop would certainly help.


Nice job maan!! Awesome.
I did some calculations: If your chrono gives 91.6m/s at 1 meter from the muzzle then the muzzle velocity must be 95m/s (assuming that the projectile is a platic bb). I also calculated that the projectiles speed at 4 meters must be 82m/s. >>The average for the sound chrono thus gives: (95+82)/2=88.5 m/s , this is really close to ur result 87.203m/s(286.1 feet per second). So in other words, for next time put the chrono half way the distance of the mic chrono length. So if the mic chrono distance is 4m then the real chrono must be placed at 2m from the muzzle inorder to get real results.
The test u did shows that the speeds are really close, but they cant be compared as u were measuring different averages. The method above should do the job.
But yeah thank u really much for testing this out, it shows that anybody in this forum can do a reasonable speed measurement. I am eager to c what further test show, but yeah just c if you have time as you wont have any use to this data anyways as u have a real chrono already :)
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 01, 2008 10:04 am

As I said, this method has its limitations - for a high velocity projectile, you'll need distance to calculate velocity in order to get a workable reading, and the further away you shoot, the less close it will be to the muzzle velocity.

However for spudgun purposes, especially for large calibre launchers firing big heavy projectiles, or lower powered BB weapons, this would seem to be a valid way of getting an idea of true velocities - props for thinking it up :)
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Unread postAuthor: frogy » Sat Mar 01, 2008 10:47 am

I think a proper chronograph or a homemade metal sensing chronograph with metal ammo would be much for accurate.

With both pneumatic and combustion guns you will have errors. Unless your guns completely silent between the time the valve open\chamber ignites and the projectile leaves the barrel...

I didn't read much of the posting at all, so if this has been discussed a lot already, forgive me.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 01, 2008 10:54 am

The muzzle blast as the projectile leaves the barrel and projectile impact - the two noises we're interested in - are easily the loudest spikes of noise in the firing process, if you're firing at a loud enough target (metal sheet etc.) and don't have a silencer then you shouldn't have problems.
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Unread postAuthor: Antonio » Sat Mar 01, 2008 11:06 am

jackssmirkingrevenge wrote:The muzzle blast as the projectile leaves the barrel and projectile impact - the two noises we're interested in - are easily the loudest spikes of noise in the firing process, if you're firing at a loud enough target (metal sheet etc.) and don't have a silencer then you shouldn't have problems.


Thats exactly what I was ganna say :) I dont know if you looked at the pics frog? Image There u can easily c that extra sounds'' dont really matter.
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Unread postAuthor: delysid » Wed Apr 02, 2008 12:43 am

could this program be used to measure rate of fire from a vortex-syle gun?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 12:47 am

You can give it a shot but I doubt you'll get sufficiently distinct peaks of individual impacts to get a reading. With a bit of work however, you can make one of these.

If you're going through the trouble though, might as well give Jim's chrono a shot, it will give you ROF and velocity measurements.
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Unread postAuthor: Davidvaini » Wed Apr 02, 2008 1:28 am

the other way you can test ROF is to take 500 BB's and see how long it takes to fire... I suppose you could record the sound and see exactly how long it fires for with audacity. But yeah then do simple math to calculate the ROF...
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Unread postAuthor: Antonio » Wed Apr 02, 2008 2:44 am

jackssmirkingrevenge wrote:You can give it a shot but I doubt you'll get sufficiently distinct peaks of individual impacts to get a reading. With a bit of work however, you can make one of these.

If you're going through the trouble though, might as well give Jim's chrono a shot, it will give you ROF and velocity measurements.


Hey Jack, I am not sure when u wrote this. But I remember you said that this method was pretty accurate right? But yeah for vortices it might be limited. If you shoot 50balls/second then you need a mic with a high bitrate/sample rate. I am not sure if the recording or the program is the limitation. When I get home ill check the smallest scale division in audicity to see how many peaks could fit in one second. The thing is that i dont have a vortex, so I never tried:)
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2008 3:00 am

I think Davidvaini's idea of taking a large sample of BBs and timing it is the easiest idea.
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Unread postAuthor: jimmy101 » Sun Apr 06, 2008 12:52 pm

Using photodetectors and a PC sound card 50 "balls/second" shouldn't be a problem. Here is what the data recording looks like for a typical vortex BBMG. There are 58 BBs in 1.5 seconds (ROF=2300 Rounds/minute).
Image
Each peak is actually two peaks since the detector has a pair of photodetectors.
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Unread postAuthor: Antonio » Sun Apr 06, 2008 1:02 pm

Pretty cool! :)
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Unread postAuthor: Sticky_Tape » Thu Jul 24, 2008 12:29 pm

Sorry for kicking up this thread but can you use 15' instead of 26.2'? I wan't to use this method to measure the speed of the bb coming out of my Marker Gun.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: Antonio » Thu Jul 24, 2008 4:04 pm

Sticky_Tape wrote:Sorry for kicking up this thread but can you use 15' instead of 26.2'? I wan't to use this method to measure the speed of the bb coming out of my Marker Gun.


Yes ofcourse. The formula is: Distance/time=speed
where distance is from the target to the target. If you leave your recording device exactly in the middle then u wont have to take into account the time delay due to the speed of sound.
If you put the recording device under the barrel or at the target then you will have to subtract (distance/1115) from the time. 1115 is the speed of sounds in ft/s. So the overall formula for recording at the barrel or the target is: speed=distance/(time-[distance/1115])
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Unread postAuthor: Wombat » Thu Jul 24, 2008 4:33 pm

Something like this was posted once before on nerfhaven, here's a link-

http://nerfhaven.com/forums/index.php?s ... hronograph
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