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Old 05-13-2012, 08:15 PM   #1
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How To Make A Homemade Chronograph

You have all probably heard of the chrono where you put the two pieces of paper a foot apart and recording the sound using audacity or similar. If so, then you probably tried it, just to discover how inefficient it is. With the echos, the sound from the gun, and the bb hitting other things, you just can't figure out which sound spikes are the bb hitting the paper. Using the same concept, you can get very accurate readings without having to fiddle with some IR leds.

Basically, you are getting the same readings, but without all the excess noise from the gun and everything else mentioned above. By using the male plug from a pair of ear buds, you can connect them to the computer and still record like a microphone.

Making the base:

You can really use any length you like but the longer the bb has to travel, the slower and less accurate it gets. But, the shorter the distance, the harder it is to distinguish the two spikes. I like the length between the two sensors to be exactly a foot so it is easier to distinguish the spikes for high powered rifles (you guys have sniper rifles I hope) and will not slow the bb down too much for any gun.

The base needs to have two holes for the sensors, so a cardboard box is good for the base. Cut them on opposite walls and have them somewhat level with each other. You also need to have them about the same size, or have the second wall (the one the bb will go through second) larger so there is less of a chance of missing and hitting the box.




Making the connectors:

This is easy if you know how to do it. You need an old pair of ear buds you don't need, or any pair of earphones. you will be cutting off the buds and just using the wire and plug. This may not be long enough depending on how long the wires are, so take some extra wire you have or go to radio shack or home depot and get some.

After getting the wire, you need to strip the ends to have the wires bare. Odds are, there will be some sort of thin enamel coating that you can't just scrap off. You will need to use a lighter or match and burn it off to make it bare. These will be used to connect to the sensors and to your computer.




Making the sensors:

The sensors are just some aluminum foil and paper sandwiches. Take two pieces of foil and put one on either side of the paper, and the other on the second side. You need to make sure they do not touch, so make the pieces smaller than the paper.

Then connect a wire to each piece of foil. Just tape it on, as you will need to take it off later to throw away the sensor and replace it. One sensor gets one pair of wires from an ear bud. It will not work if you take one wire from one bud, and another from the other and put them on one sensor.




Place the sensors on the base:

Tape the sensors over the holes you made previously in the box. Try to have the wires not over the holes so you can't accidentally shoot them.



Use it:

Now that you have it made, you need to know how to use it. Get a program like audacity or anything you can use to record and see the sound levels of the recording. I like recording at 48000hz because my computer is not fast enough to record at 96000hz.

1) Start recording
2) shoot through the two sensors (use foam or more cardboard as a backstop)
3) Find the two spikes in sound level and zoom in until you can see it up close
4) Find how long it took for the bb to pass from sensor one to sensor two
5) Divide the distance by the time to get speed. ex: 1 (foot) / 0.002 (seconds) = 500 (fps)



Hope this helps. If I made any mistakes or if you think you can make modifications, I'm open to suggestions!
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Old 05-13-2012, 09:43 PM   #2
 
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I like it, but won't foil slow the bb down quite a bit? What about something more like tissue paper?



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Old 05-13-2012, 10:08 PM   #3
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The foil would indeed slow down the bb a bit, but probably not too much. I haven't gotten to test how much though, but for our purposes as soon as we find that out we can factor it into the rsults and it will be fine. Although I don't have a chrono so someone else will have to do it. That's why I made this. Its never going to be professional chrono accurate.

I did not think of tissue paper. I'll try that out tomorrow, but I'm afraid the bb might actually pull the tissue paper with it and might block he foil from connecting. Or I might just be over thinking this. If the tissue paper works I owe you a thanks for making it even more effective.
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Old 05-13-2012, 10:35 PM   #4
 
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If you hit it hard enough with a bb, it will go right through.

It's worth a try, at least. ;)



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Old 05-14-2012, 06:49 AM   #5
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I know it will go right through, but it might pull some of the edges is what I meant because it is much more malleable than paper. Paper will try to hold it's shape while tissue paper will not.
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Old 05-14-2012, 05:50 PM   #6
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I tried using the tissue paper, and it did give a 5 fps average gain with my 200-220fps pistol. But the readings were so inconsistent because the tissue paper does not hold it's shape, it took five tries to get a reading legible enough to do the calculation on. If you see on the audacity screenshot above (used the same pistol with that one as I tested with tissue paper), you can clearly see the impacts. I just couldn't get that kind of clarity with tissue paper. And using higher powered guns just makes it worse.

So really, for a 5fps gain, it's not worth the tissue paper. It was a great idea though.

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Old 05-14-2012, 06:37 PM   #7
 
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Well, worth a shot... :P



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Old 05-14-2012, 08:36 PM   #8
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If you've got a chrono, it only takes 20 minutes to make this and see how much impact the sensors on my improvised chrono have on the fps. It would be great to know so we can factor it in.

I'm also going to try to get a hold of some tracing paper because it is much thinner than computer paper, but not too pliable like tissue paper.
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Old 05-14-2012, 09:13 PM   #9
 
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I don't have a chrono right now, I just use the one at the local shop.



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Old 05-16-2012, 10:13 AM   #10
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I got some of that ultra thin sketching paper and it gave me about 3 extra fps in the tests. Not worth buying specially made thin paper haha.
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Old 09-06-2012, 05:46 PM   #11
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UPDATE: I found out this makeshift chrono gives a significant loss of fps compared to a chrono, although I don't know how much. If anyone has a chrono already I, and others would be grateful if you could compare results with the makeshift chrono and a real one. If you have different powered springs or gunsN or an adjustable HPA rig we could make a small chart and see if the drop in fps is linear or not as the real fps rises, then we could predict and fill in the rest of the chart. Thanks.
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Old 09-07-2012, 12:43 AM   #12
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I'm wondering how well it would work if you used wax paper instead of the tin foil, and then set up a microphone to capture the sound as it goes through the first and second sheets? You should get two distinct sounds as it pops through the wax paper, which would give you your spikes on the audio recording! I'll see if I have time to give it a try and then compare it to my chrono!
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Old 09-07-2012, 02:38 PM   #13
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That was what I tried first actually. I found that with echoes and the sound from the gun, you just can't get two clear spikes like with this method. The few Times I could find the sound spikes, the readings were almost 70fps apart, which can be a big difference if you are making sure your gun is field legal.

This is the most consistent makeshift chrono I have tested so far, and it is comparatively easy to make compared to a more complicated IR LED based one, which you would need basic electronics skills to make. The IR version might be more accurate and has nothing to slow the bb down besides air, but if you use CO2, propane (green gas), or something similar, it can screw up the results. It is probably easier to find the sound spikes in my version anyway because the foil and paper slows down the bb, making the sound spikes farther apart.

And thanks for volunteering to compare results!

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Old 10-14-2012, 12:48 PM   #14
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Quote:
Originally Posted by Masterjuggler98 View Post
UPDATE: I found out this makeshift chrono gives a significant loss of fps compared to a chrono, although I don't know how much. If anyone has a chrono already I, and others would be grateful if you could compare results with the makeshift chrono and a real one. If you have different powered springs or guns, or an adjustable HPA rig we could make a small chart and see if the drop in fps is linear or not as the real fps rises, then we could predict and fill in the rest of the chart. Thanks.
Still need someone to compare the makeshift chrono to a real one. This can really help people with a low budget and don't have a real chrono.
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Old 10-20-2012, 10:04 PM   #15
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Bueler? Ferris Bueler? All I'm asking is you make this simple setup and compare it with a real chrono. Wolf, not trying to put you on the spot or anything but I know you have a good chrono. Do you have the time?
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