Simple DYI Chronograph

Thanks to The Ran for this -ible, since he pointed out this project.

The idea for this instructable is pretty simple, v = d/t.
Projectiles have velocity, and it's nice to know how fast you're shooting especially for airsoft and school physics projects. Unfortunately, commercial chronographs are fairly expensive, and not everyone has the electronics skill to construct some of the more professional DIY setups.

This instructable shows a simple technique to get a rough reading of how fast a projectile is traveling based on sound. Here we go.

Step 1 Parts

for this project, you will need...
at least one microphone
a calculator capable of at least 8 didgits
the open source Audacity sound recorder
a computer to load Audacity on (windows/linux/Mac(BSD too..))
paper or a can (a cardboard box'll do)
a way to sling something reasonably fast (and preferably generate a sound)
a tape measure

Comments

[Kush_Slayer]

wow i should go and fire a .50BMG rifle and try and find out the muzzle velocity this way, time to start trying to find the bullet lol

[Knex_Gun_Builder]

if you had a 50 BMG rifle that costs in the neighborhood of 10,000 dollars, and loaded amunition that is $10 a shot, I would think that you could spend the extra $150 on an ACCURATE chronograph.

[sokamiwohali]

besides...a .50 BMG isnt a rifle...its a frickin machine gun...(i was an ammunition specialist for the army. my job to know)

[knexdestroyer]

Some rifles made by Barrett shoot the .50 BMG like the m95 and the m82. .50 BMG was first used in HMG first though

[sokamiwohali]

i deal with ammunition in the Army, and the bullet round isnt .50BMG. its just a .50 cal round. the only difference in a MILSPEC .50 cal round and a civilian is that a military round is catered to and the casings are a bit different, and a civilian round isnt.

[Knex_Gun_Builder]

Then why do the chamber reamers say 50 Browning Machine Gun and not "50 cal?" I have fired two 50 BMG rifles, and they are stamped on the barrel 50 BMG. You are correct that the 50 BMG cartridge was first used in machineguns like the BROWNING M2HB, but it was soon adapted to rifles. if it was a "50 cal" then it would be rather confusing, with all of the 500 asquare rifles and 500 s&w handguns running around, wouldnt it? i do understand that 50 cal is a rather popular nickname for the 50 BMG, though.

[subseashane]

Used Garage Band .023 seconds of flight for 111 inches = 402 ft per second. little fast.
Thanks for the idea to use a sound application.

[matt2485]

why would you spend so much money and time on this

[baneat]

Tape measure
Microphone
Freeware

eh I have all this available for free, so no money there. There are genuinely useful applications for knowing the speed of the projectile, and it doesn't take long. Plus, you're on a DIY site, as far as practical applications go this is one of the best. People spend far more time, and far more money for much more useless stuff than this

[knex_mepalm]

 The formula is all multiplications right? Because....According to many other websites and this test I threw a ball at 153 fps. I mean, I was stunned but, it must be wrong.

[LordSnipe]

nope, no multiplication unless you count inverse multiplication.
v = (d/t)
d = distance between the two sheets/plates/objects
t = difference in time as shown by the audio graph.

[Nexu]

Depending on how far you threw the ball it may have been going that fast.
If you threw it a far distance it may not seem that way because it loses speed faster than a bullet or bb would because it is larger and there is more surface area for friction.

[knex_mepalm]

100m or so, im accessing this webpage from school!!!

[notyou13]

same! lol pie

[M4industries]

 Ninja Proxy is amazing!

[arkz09]

is that proyectal motion ??

[LordSnipe]

Is there gravity?
Yes. This is projectile motion, but the difference due thereto is for any projectile of v >= 75 m/s that over 1m, the change in altitude should be negligible.

[sabladask]

hey.
what wil hapen if the bb travels faster than the speed of sound( 1020 fps)?

[LordSnipe]

.... in the case that you have a bb or other projectile moving that fast, you would be better served by a commercial chronograph than my hacked-together method. Theoretically, this technique will still work, but the odds are that the microphone will be overwhelmed by the supersonic shock wave. You would do better to have to mics some distance apart and compare the time it took for each mic to hear the shock wave. That's how most commercial chronographs function.

[firefletcher]

Very easy, Just did it with my slingshot and got 70fps with practice ammo. I will try again tomorrow just to make sure. Thanks!

[di11on]

A further comment I have is this...

If using the gun and 1 target method with an airsoft gun, you have to measure the distance from where the piston strikes the projectile (where the barrel starts) as this is where the projectile is when the firing sound is generated. This can be a significant source of error if measuring over short distances.

[di11on]

It's not technically true that it doesn't matter how far apart your targets are because the projectile is slowing down as soon as it leaves the muzzle. What you are, in fact, measuring is the average speed of the projectile over the distance from muzzle to target. Usually, the instanteous muzzle velocity is of greater interest than the average speed over a set distance.

So what you have is a trade off. The closer the targets, the less the speed difference over the course of the trajectory, but the greater the error in the measurement. The further the target is, the greater the accuracy, but the more you are only measuring average speed, not the muzzle exit speed.

[Eddiepers]

accorging to mine, my modified nerf gun shoots 610 fps muzzle!!

[mr. cool 384]

thats like pellet rifle power

[mattyts]

this dosent work .......acording to this my slingshot is 30fps and my bb gun is 2fps

[knexsuperbuilderfreak]

i did this my bb gun was 4 and its power full it can make dents in wood 100ft away

[mr. cool 384]

2fps, thats like................i cant even think of somthing thats that weak

[Zaphod Beeblebrox]

a realy tired 3-year old rolling a bowling ball up a hill

[mr. cool 384]

lolololololololol im sure u would know about that

[Zaphod Beeblebrox]

yep i would

[eneergcam]

why, are you a pedophile who hunts tired 3 year olds? hahaha jk

[2743]

mine also does not work. it says my airsoft gun speed is 106fps. but my airsoft gun could penetrate through a wire gauze(fine and medium hard one) from 5metre away.

[davidemil55]

probably doing the math wrong

[firefighter1333]

lols, if that would be thru...

[LordSnipe]

what where the numbers you got? post them and maybe I could help. I need to know.. dist between the papers elapsed time between papers or you could just re-do the experiment.

[sharlston]

hi this is mattyts but on my other account the numbers i got the distance was 3 feet thime was 0.243 seconds and i shot a bb

[LordSnipe]

okay.. that solves to 12.3 FPS. re-read the insturctable and try again, I DID MAKE SOME CHANGES THAT SHOULD HELP. I assume that punching through two pieces of paper is killing your projectile's speed

[firefighter1333]

i think u'd better ask that to mattyts cuz i dont even hav a slingshot....

[sharlston]

well if you want to talk to mattyts talk to me its my other account!

[Vertigo666]

Haha, physics (or as my teacher says, fizzx) at work
In the raw form, the formula is
T = (v)(Fg)(D)(0.5)
This formula is for seeing how long it takes for the bb to travel up to the maximum distance as allowed by gravity, so the result should be a little lower than horizontal velocity.
Oh, btw, is 3.2808 the conversion factor for meters to feet?