SpudFiles

I have been looking around my town for a place where i can use a chronograph, but have been unable to find one.

The paint ball store wont test homemade guns, the gun ranges will only test explosive powered, lead flinging weapons. I got the same answer every place i tried.

The paintball store, however, sells chronographs, for 120 bucks.

So, seeing as i am a poor student, i built my own, for under 20 bucks.

Here is how i did it:

WHAT YOU WILL NEED:::::::::::

2x infrared phototransistors RADIOSHACK
2x infrared LEDs RADIOSHACK
4x 1/2'' PVC end caps. (to mount the LEDs and transistors in)
1x wooden plank, flat and at least 1.5' long and 3'' wide.
1x AA battery and holder
1x computer
1x 1/8'' x 1/8'' headphone style wire.

A bunch of hook-up wire,
some solder, and a soldering iron.


INSTRUCTIONS:

Drill hole in the caps, for the LEDs and transistors, put transistors and LEDs in caps, glue in place.

Wire the transistors in series, and the LEDs in Parallel, on 2 seperate circuits.

Hook the battery holder to the LEDs, and the headphone cable to the transistors.

Glue the LED circuit to the wood, so that the LEDs are 1 foot apart, and point across the plank.
Glue the transistor circuit so that the transistors point towards the LEDs

put the battery in the battery holder to power the LEDs. Care full, they are infrared, and cant bee seen with the human eye. Take a digital picture of them to see them "On"

Hook the transistor circuit up to the line-in or microphone jack on your computer, open audacity, or some other recording program, start recording sound.

shoot your projectile through both "gates" and then stop recording.

If you look at your recorded sound file, you can see 2 "Peaks" each peak is a photo gate signaling that there is a bullet in the middle of it.

Muzzle velocity can the be calculate with this formula:

Mv= 1/(Time1-Time2)

Mv is the muzzle velocity in FPS
Time1= the time in your sound file when the first gate was broken(Peak1)
Time2= the time in your sound file when the second gate was broken(Peak2)

This equation assumes you have your gates 1 foot apart. if they are 6'' apart, then:
Mv=1x(gate distance in inches / 12'')/(Time1-Time2)



MUCH more detail can be found on this web page.(Not by me)
http://www.inpharmix.com/jps/Jims_chrono.html


PHOTOS:





Edit by MrC:
Dear author,
Do not request topics to be stickied.

EDIT: Yes sir MrC

Here is an example file....Click to make it bigger

That looks great mate. If not stickied, it should at least be in the How To section. But great job on the manufacture and write up. Considering making one myself

Nice although the website you linked to is jimmy101's (or something like that) I don't know if he posted a how to on it but hes defiantly linked to there before.

Maybe a wiki page is in order.

jonnyboy wrote:Nice although the website you linked to is jimmy101's (or something like that) I don't know if he posted a how to on it but hes defiantly linked to there before.

I am not trying to claim it as my own design, i said that the site was not my own.

~Jhalek90

would this be able to detact a 6mm bb going 1200fps

How accurate is it? Have you compared your results to that of GGDT's?

yes i have it more of a 12 foot gun it more of a station or train cannon then a gun

twizi wrote:would this be able to detact a 6mm bb going 1200fps

I am not sure how fast the Radio Shack transistors are, but some old surplus ones I have from long ago are not fast enough. I need to get something faster. If you know how to use photo diodes instead, the ones in CD players in the pick up are fast enough. I need to grab a few drives and raid the pickups. Bare photo diodes are very static sensitive. Use ESD workstation.

If using Microsoft Sound recorder or other capture software, find the length of time the BB will block the sensor. Use the 1/X division to convert time to frequency and be sure your sample rate is high enough to capture at least 3 samples in that time. Otherwise your capture may miss the event. This is most true for smaller fast projectiles. They don't block the beam very long.

here are a few samples files.



3 points/0.0005 seconds

1/0.0005=20,000 samples.... but there are 3 per 0.0005
so 20,000x3=60,000 samples/second.

If my numbers are correct.

PS: in the file above, a bouncy ball was clocked at 238.09450... FPS

PPS: I plan on making a program in the next few days, to do all the math for you, jut press a button, shoot and it spits out the FPS on screen.
Should i release it with these plans???

jhalek90 wrote: PS: in the file above, a bouncy ball was clocked at 238.09450... FPS

Not bad, what cannon was that with?

BTW, if you clean the topic up and make it more clearer and easier to follow with some pictures and diagrams to help, me or another mod might sticky it. There are other how-to's like this, but if you make this good enough it could deserve a sticky.

Agreed, perhaps a simple circuit diagram would be helpful

MrCrowley wrote:

jhalek90 wrote: PS: in the file above, a bouncy ball was clocked at 238.09450... FPS

Not bad, what cannon was that with?

BTW, if you clean the topic up and make it more clearer and easier to follow with some pictures and diagrams to help, me or another mod might sticky it. There are other how-to's like this, but if you make this good enough it could deserve a sticky.

The 1'' bouncy ball pistol. at 35 PSI

I will clean this up, and make a better how to tomorrow, as i am going to bed soon.

Night all

jhalek90 wrote: The 1'' bouncy ball pistol. at 35 PSI

Thought so, fairly good for such a small launcher and low pressure.
Sounds about right, 240fps with that cannon.

MrCrowley wrote:

jhalek90 wrote: The 1'' bouncy ball pistol. at 35 PSI

Thought so, fairly good for such a small launcher and low pressure.
Sounds about right, 240fps with that cannon.

Yes, i was quite happy with that shot, for only using 35 Psi. haha

Here is a simple wiring diagram i just made in photoshop.... not to good... but easy to follow if you know anything about electronics.




Full blown how to write up tomorrow!!!! (If i get around to it... lol.)