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The Homade Chronograph (accurate too!)

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The Homade Chronograph (accurate too!)

Unread postAuthor: VH_man » Sun Mar 11, 2007 7:31 pm

Well, its not my idea, but its simply ingenious. ill put a copy and a link to the original website. just wanted to share it with people, its just too cool!
And, by the way, this can measure up to 1000 FPS. its a little hard to get the distance found, but its there. Also, for mine, i used speakers as michrophones, they are less sensitive to ambient nosie and pick up loud pops, like the nosies made in spud guns and objects colliding with one another. i know this article is nerf, but it works for other stuff too....

http://www.nerfhq.com/smf/index.php?topic=4210.0


Folks, after playing with this all night . . . . this is the NEW STANDARD in testing your nerf gun mods.

In the past someone posts ranges and people ask," Was it level? Angled? Wind? Skip? etc. etc."

We want to measure VELOCITY of the darts. This is just like every other gun out there. Paintball, Airsoft, etc. They are all measured in feet per second (FPS)

I wanted to be able to tell without a doubt that one barrel length is better than another, or this type of stefan is better than another and so on. Wanna know EXACTLY how much faster your darts go without restrictors in it?

A chronograph is a device that measures velocity of a projectile, usually in Feet per Second. These arent cheap, usually around $50 cheapest and they dont even go low enough to measure a nerf gun. what to do . . .

Heres the basic idea:



The tip of your barrel is placed exactly 10 feet from a piece of paper(suspended between two legs of a chair or whatever).

Use a audio splitter from your computer to two microphones, one place by your gun and one placed behind the piece of paper.

I used this model available from Target (and their website) for $9.99



next download the free software called Audacity http://audacity.sourceforge.net/

This program will allow you to record sound and then go back and select specific points in time. With the chrono set up, hit record and fire your gun from exactly 10 feet away at the piece of paper. When you review what you recorded it should look something like this.



Now select the very front/beginning of the first sound (gun firing) and drag it to the very front of the second sound(dart hitting paper). It should now tell you exactly how long it took for the dart to travel 10 feet, to the nearest .0001 second!

Do this 5 times for an average time and then go on to your next modification and see how much of a difference it made.

A typical totally stock gun will be in the .35 second range.

Now we want to convert that time into FPS (feet per second)

The formula is : 1/(your time) X 10

For example: my bone stock Nitefinder had an average time of .3715 seconds. 1 divided by .3715 times 10 = 27fps(feet per second)


I tested this out all night on a Nightfinder and a Longshot. I cant believe how accurate and consistent this setup is. I recorded 5 shots each time and averaged them for each mod.

I will be posting a complete writeup on the nightfinder and possibly the Longshot using this method. Let me tease you with this . . . A stock NF shoots on average 27fps and mine right now is shooting at 88fps and i havent even put a brass barrel on it yet!!!!

Here is a picture of the setup in my living room
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Unread postAuthor: Killjoy » Sun Mar 11, 2007 7:46 pm

I remember readin about this somewhere and had a friend try it, like you said it works pretty well. A ballistics pendulum also works well for this kind of thing. Still the limitation of about 1000fps is a shame, might just be cheaper and easier to buy a new Chronograph for like 85 bucks.
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Unread postAuthor: Matheusilla » Sun Mar 11, 2007 8:02 pm

You can also use a digital camcorder and calculate with the frames per second. The better the camera the more accurate measurement.
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Unread postAuthor: Bluetooth » Sun Mar 11, 2007 8:02 pm

This isn't new... That person didn't come up with it either.
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Unread postAuthor: willarddaniels » Sun Mar 11, 2007 8:11 pm

An even more accurate method would be to set up two sheets of paper, 10 feet apart. Measure the time between the projectile hitting paper 1 and paper 2. This will measure the precise fps.
The problem with only having one sheet of paper and using the combustion as the starting point is that you are not compensating for the slower speeds throughout the acceleration and your reading is now a lower fps than what it actually is. You can determine this velocity, but that is not the point here.
Also, if you use the one sheet of paper method, you need to start measuring from the rest position of the projectile in the cannon, and not the end of the barrel. The combustion and acceleration starts when the projectile is at rest, not when it is at the end of the barrel. Measuring from the end of the barrel will give you a higher fps than what is probably happening. Think about it: If you have a 5' barrel and the sheet of paper is 10' from the end of the barrel, your 10' just turned into 15', a 50% increase.
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Unread postAuthor: VH_man » Sun Mar 11, 2007 8:30 pm

why would you need to start there. were measuring muzzle velocity........ not projectile acceleration. and the problem with the two peices of paper is that the first peice slows the projectile down enough to not give it a good reading. it might be accurate enough for spuds/marbles, but for airsoft (the thing i use this thing for) it results in an FPS measurement decrease of over 20 FPS.....
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Unread postAuthor: willarddaniels » Sun Mar 11, 2007 8:39 pm

Then use 3 or 4 sheets and extrapolate the effect the paper has on reductions in velocity to get your muzzle velocity. This would most likely be more accurate then having the fudge factor of the acceleration turning your figures into a guessing game. At least with 3+ pieces of paper, you have some reliable data to base your calculations on and not so much speculation.
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Unread postAuthor: MrCrowley » Sun Mar 11, 2007 10:13 pm

Oh yeah this......Ive heard about it else where.....
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Unread postAuthor: risto » Sun Mar 11, 2007 10:34 pm

why wouldnt one microphone work by the paper? obviously your spud gun is loud enough to be heard on it, or is this because that 10 feet can throw off the time sound takes to travel 10 feet (which is millisecond)?

just a thought
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Unread postAuthor: MrCrowley » Sun Mar 11, 2007 11:02 pm

if you have the recording device in the middle that problem would be eliminated.
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Unread postAuthor: homedepotpro » Sun Mar 11, 2007 11:09 pm

OK i tried it just as described an it worked better than i thought
-these are my results:
1. 60psi - 348fps
2. 60psi - 372fps
3. 60psi - 355fps
4. 90psi - 436fps
5. 90psi - 480fps
6. 90psi - 450fps
7. 90psi - 469fps

they seem correct to me
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this was the setup
CIMG0184.JPG
this is the gun and ammo
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Unread postAuthor: willarddaniels » Mon Mar 12, 2007 11:55 am

I guess my point in the multiple sheets of paper is to be more accurate in measuring the projectiles of normal to larger cannons. If VH man is firing cannons where the projectile
A stock NF shoots on average 27fps and mine right now is shooting at 88fps and I havent even put a brass barrel on it yet!!!!
is quite a bit slower, then going through just one sheet of paper will significantly slow down the velocity of his projectile, thus making it impractical.
For most spudgunners like homedepotpro, the 2-3 sheets of paper would be much more accurate. When using the 2-3 paper homemade method, use darts (pointy projectiles) to reduce the loss in velocity.

My apologies for missing the speed you are trying to measure. The difference - percentage wise - would be much more on a slower gun.
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Unread postAuthor: homedepotpro » Mon Mar 12, 2007 11:36 pm

yeah but the problem is that the muzzle noise echo, so you need a distinctive and loud noise made by the projectile's impact. thats why i used a blunt dart for ammo and a stiff cardboard box as a target
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Unread postAuthor: VH_man » Tue Mar 13, 2007 11:00 am

Try using speakers as michrophones. they react to high-intensity sound waves, unlike electret michrophones, which react to any noise. make sure you have big speakers though, like subwoffers or cabinet spekaers. i found mine in a junkyard......
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Unread postAuthor: homedepotpro » Tue Mar 13, 2007 9:21 pm

how do you set those up
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