Homemade chronograph

[Antonio]

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.

I dont think it matters if you take it from the begining. All my guns have very light triggering systems, so a pull of the trigger will result in a direct launch'' (only milliseconds). For spud guns it easier as they use only one volume of air (too much), there u can clearly c a peak. But yeah using audicity you can select only a part of the track to listen to it. Like that u can hear if its a high or low pitched etc. High being the trigger and low the air for example.

[jimmy101]

@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

Well, it'll depend a lot on what you are firing. A combustion spud gun is no problem. Mic at barrel, mic 20' away, ... not much difference. Only problem is echoes, which can be confusing.

A BBMG is no problem with the target within a foot or two of the barrel and the mic equidistant.

A sound card will usually sample at up to 48KHz. That means it is taking a sample every ~21uSec. A projectile moving at 500 fps takes 2,000uSec to travel 1 foot. So, for 500 FPS and a distance of 1 foot there are ~100 samples in the recording. The sample rate error is just 1%, more than accurate enough. Really no need for the target to out at tens of feet from the barrel.

Of course, the faster the projectile is moving the larger the distance you want. But even with a 1000 FPS shot a 1 foot seperation is only going to have a 2% sampling error.

[ghostman01]

i still dont get the formula could you right its out explaining it a little more please i know you dont have much time but yeah

[Antonio]

i still dont get the formula could you right its out explaining it a little more please i know you dont have much time but yeah

Hey, I tried to simplify the formula by putting in valves that I choose for the ppl. If you put the mic below the barrel of the airgun u use this formula: Speed = Distance/(time-(distance/speed of sound))
To keep it simple I will refer to meters. The speed of sound is 340m/s
As you may have learned in physics speed= distance/time
In this case I have a speed of sound correction factor as it takes some time for the sound the projectile makes on impact to reach back to the mic. This time correction factor is dependend on the distance ur target is at. So thats where it comes from. Distance/Speed of sound=m/(m/t)=t
Hope this helps

[ghostman01]

lol i havent done physics yet but i understand now lol

[BigGrib]

@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

Well, it'll depend a lot on what you are firing. A combustion spud gun is no problem. Mic at barrel, mic 20' away, ... not much difference. Only problem is echoes, which can be confusing.

A BBMG is no problem with the target within a foot or two of the barrel and the mic equidistant.

A sound card will usually sample at up to 48KHz. That means it is taking a sample every ~21uSec. A projectile moving at 500 fps takes 2,000uSec to travel 1 foot. So, for 500 FPS and a distance of 1 foot there are ~100 samples in the recording. The sample rate error is just 1%, more than accurate enough. Really no need for the target to out at tens of feet from the barrel.

Of course, the faster the projectile is moving the larger the distance you want. But even with a 1000 FPS shot a 1 foot seperation is only going to have a 2% sampling error.

record one mic on left and one on right channel that way everything sync's up and you can see the echo's where the echos are versus each channel. it's really really easy

[tomthebomb137]

has anyone ever heard of a balistic pendulum? because from what i understand they can also calculate your muzzle velocity with no electronic componets, and can be built for like 5$ from household components

[Ragnarok]

Ballistic pendulums are a little more complex than just that, and probably a bit more expensive. To get a good result, there's quite a bit of extra maths to consider, and a lot of people don't like that.
Unless they're pretty well built, you may well have problems getting a good value from one.

Spudguns aren't ideal for BPs, mostly because of odd ammunitions and high projectile momentum.

It's an option, but as a couple of phototransistors and LEDs rigged up right can often do the job better, and for less cash, I can't see them becoming popular.

[jackssmirkingrevenge]

just buy one

[jimmy101]

Ballistic pendulums are a little more complex than just that, and probably a bit more expensive. To get a good result, there's quite a bit of extra maths to consider, and a lot of people don't like that.
Unless they're pretty well built, you may well have problems getting a good value from one.

Spudguns aren't ideal for BPs, mostly because of odd ammunitions and high projectile momentum.

It's an option, but as a couple of phototransistors and LEDs rigged up right can often do the job better, and for less cash, I can't see them becoming popular.

My son built a Ballistic Pendulum out of his Lego Mindstorms set. Basically a bucket at the end of an arm, the axle of the arm geared up a bit then it's rotation measured by a Mindstorms rotation sensor. Simple little program on the Mindstorms cpu "brick" to detect and display the maximum rotation angle. Worked OK.

But a MIC and a PC with soundcard was simpler and more accurate.

just buy one

Oh, you're no fun.

[Antonio]

[quote="jimmy101]My son built a Ballistic Pendulum out of his Lego Mindstorms set. Basically a bucket at the end of an arm, the axle of the arm geared up a bit then it's rotation measured by a Mindstorms rotation sensor. Simple little program on the Mindstorms cpu "brick" to detect and display the maximum rotation angle. Worked OK.

But a MIC and a PC with soundcard was simpler and more accurate.

[/quote]

I built a ballistic pendulum before. The problem is that the full energy needs to be converted into potential energy. So in other words you have to shoot in a cup with clay or something. My problem was measuring height that the cup gained. As I hung the bucket on strings it didnt always move in a perfect straight line'', but sideways. As jimmy says my method using a mic is so much easier and more reliable.
Btw I dont agree with rag; this method doesnt involve sophisticated maths. Its: 0.5mv^2=mgh where h is the height the bucket has achieved with m of the bucket+the projectile. >>v=((2*(m+M)*9.81*h)/m)^0.5 where m is the mass of the projectile and M is the mass of the bucket.


MERGED:

just buy one

....$70 damn. Btw could you compare u chrono to this method sometime? Maybe noone has to buy a chrono, but we have to just add a correction factor to the method that I prescribed here

[tomthebomb137]

i remeber my lego mindstorms kit 8)

[jackssmirkingrevenge]

Btw could you compare u chrono to this method sometime? Maybe noone has to buy a chrono, but we have to just add a correction factor to the method that I prescribed here

I'll try and do it this morning if I have time, finally found my microphone

[Antonio]

Btw could you compare u chrono to this method sometime? Maybe noone has to buy a chrono, but we have to just add a correction factor to the method that I prescribed here

I'll try and do it this morning if I have time, finally found my microphone

Coola, thnx.
Edit:
Maybe its too late, but you get best comparison if you place the chronograph half way the length that is used for the mic chrono. As the mic chrono measures average speed over the distance. It would be most likely that this would be around the middle point of the distance travelled>

[jackssmirkingrevenge]

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.