Audio Chronograph

    Ok guys I searched a bit and did not find anything related to this. I must admit that this is not originally my idea; I saw this somewhere in the bowels of the internet with regards to airsoft using two sheets of paper and two microphones. I have somewhat heavily modified it to paintball and simplicity.

    This method relies heavily on one - if not the - best free audio softwares available. You may download and read more about it here. The program has a very simple interface, play record pause etc., and a simple and useful highlighting and zoom feature.

    Now let’s get to the real point of this post. I like may people do not have a chrono but I recognize the need of one. This setup requires a microphone, laptop or long mic cord, paintball gun, tape measurer, and hard surface (tree, fence, car, 15th century Chinese vase, etc.) I chose a good distance from my chosen tree that I knew would allow me to easily stand in the same spot each trial, there happed to be 42' between my barrel and the tree, this number is important.

    I placed my mic halfway between my gun and the tree. Where you put your mic is not important as long as it is in line with you and the tree.

    Next just load up Audacity, hit record, get into position, and fire away. Not to fast. You don’t want more that one ball in the air at a time. When you are done shooting, 4 shots sounded nice to me, hit the spacebar on your computer (stops the recording). Hopefully you get something like this, minus the yellow highlight I added.


    First you see 4 sets of one big spike followed by one little spike. After that the jumble is a half hearted attempt to measure my bps. You want to zoom into one of the sets of spikes including a little extra like what is highlighted in my picture. Do this by clicking and dragging and pressing the button.

    This should give you something like this.


    Continue by highlighting as shown. I chose the second large spike because I figured it was closer to when the paintball actually left my barrel, and if it wasn't, it would result in a shorter time thus higher velocity, this may give you a reading for higher velocity than you are running which is not as dangerous as a thinking your velocity is lower than it really is.

    The time between spikes is easily found in the yellow highlighted section. My time was .185663 seconds. The ten thousandth place should be accurate enough for this exercise so for this calculation I would use .1857.

    Now you can’t just take distance over time here, 42/0.1856 would give me 226 fps and that just isn't right. So I had to unexpectedly take into account something else.

The speed of sound.
    So as we all know the speed of sound at sea level is 1,100 fps, I'm not sure how much it varies with elevation, humidity, and phase of the moon so I just used 1,100.

    Now to include the speed of sound we need to know how long it takes the sound to get to the microphone from its source. Now as long as your mic is inline with the gun and hard surface the time I need to subtract from my .1856 number is the time it takes sound to travel that entire distance. For me 42/1100 is .038181818 seconds. Again rounded to .0382. Your actual time will be .1856-.0382 or .1474 seconds.

    Finally distance over time is 42/.1474 or 284 fps. See how much the speed of sound matters. And this I feel is a good chrono substitute.

Now for things that I may need to consider

• Over 42' drag will slow down the ball. To account for this we need the formula for the force of drag:

Force of drag = .5(Coefficient of friction)(density of air)(Affected Area)(velocity)²

Then to get the change in velocity you would need F=ma to find acceleration, next you need v = v₀ + (a)(t) and some maybe some calculus for point blank velocity.

• Because of drag this is an average the fps will be higher than 284 at the barrel and lower than 284 at the tree.
• I would like somone to check this against an optical chrono. I believe it is quite accurate.
• Different guns/barrels/setups will give different shot spikes so be careful what spike you choose
  

About me
I was on the forum quite a lot 3 years ago, stopped paintballing for some reason. Luckily I'm back into it. Unfortunately my old member name was deleted. Not a big deal. My gun is in the sig, it suits my needs especially cost. I hope you find this as cool/useful as i did, even though it feels like a final for physics class

Edited by Olcaddy - 14 July 2006 at 3:49am

    Its not so bad, I could simplify it but I like people to have a grasp of things they use. I like people knowing how their gun works, how thier car works, and how their cool audio chronograph works. I may edit this post with a simple version with just distance and time as variables.

Oh and "Cadillac: Going fast with more class" I have a 1969 Deville Convt.

Ok the simplest way I think I can get it is this.
If you read my first long post, in this formula D(Distance) for me was 42 feet, t(time) for me was 0.1856

fps =  D/[t-(D/1,100)>


Edited by Olcaddy - 16 July 2006 at 4:45pm

284 isnt over at every field.  I think its 290 or 300 limit at my field.

The shot and the splat show up as clear spikes as you can see. I did this outside of course so there was some wind/birds, no cars or roosters or anything loud but anyplace you would shoot off some rounds of paint should be quiet enough

Not a bad idea, and reletively cheap. I could make a java based program to run the numbers and host it somewhere. Thats if I got around to it lol.

if its accurate it would be sweet cause chronos cost wayyy to much !

I like It works.

this is really cool, however like a lot of other people you lost me in the math. (stupid math)

adblink wrote: this is pretty sweet, has anyone compared it to a real chrono? also does it matter where the mic is placed between the target and the gun? as long as its under 20 feet and anywhere in the middle should be fine?

Well, right now Im working on one to account for the drag, and to make it all look better.
But the mic can be at the tip of the gun barrel to the wall.

This is actually really fun, Ive been wanting to use this java for something. lol.

EDIT:
This version you dont have to reload the page to do another computation.


<html>
<body>
<SCRIPT TYPE="text/javascript">
//writen by Joshua Stuckey
function PaintBall()
{
var time = document.speed.time.value;
var distance = document.speed.dist.value;
var sof = distance / 1100;
var ntime = time - sof;
var fps = distance / ntime;
document.speed.fpsface.value = fps;
}
</script>
Place the microphone between the barrel and the wall, and record the time.
<form name="speed"><br>
Time:
<Input Type="text" name="time"><br>
Distance:
<Input Type="text" name="dist"><br>
<Input type="button" Value="Calculate FPS" onClick="PaintBall()">
<Input type="text" name="fpsface">FPS
</form>
</body>
</html>

There ya go dudes. All cleaned up. Still no drag, so its still only accurate to about 20ish feet. So add about 5fps.


Edited by Monk - 15 July 2006 at 4:30am