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Why the home made chrono systems?

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Why the home made chrono systems?

Unread postAuthor: D_Hall » Sun Nov 22, 2009 1:51 pm

I've seen something on this forum for a very long time and I've never understood it: Home made chronos.

Why?

It's not like commercial chronos are particularly expensive or difficult to aquire. Why not just go buy one? I could understand if the chrono was in and of itself a little project/hobby, but I don't get the idea that's what's done around here. Why not just buy one and be done with it?
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 22, 2009 1:55 pm

I often point this out whenever someone asks about "rolling their own", I think the main reason is that many imagine them to be so pricey that they don't even bother checking out the actual cost, as little as 70 dollars will get you a perfectly suitable F1.
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Unread postAuthor: psycix » Sun Nov 22, 2009 2:04 pm

When I wanted to have a chrony, I considered building one too.
However, this would take some time for research, acquiring components and construction. On top of that this yields a lower quality chrony, and probably less compact too.

I then thought: If I would spend all the hours of research, design and construction in a job, how much money would I earn?
Well, enough to add just a few bucks and end up with a real chrony, being reliable, precise and compact.

Think of money as being time, and then check out how much something costs compared to building your own.
Quick example: I could build a 1/2" barrel sealing piston valve. I could also buy a QEV.
For just a basic gun, I would probably spend less money and time (but time = money) on the commercial factory made QEV then the homemade one.
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Unread postAuthor: D_Hall » Sun Nov 22, 2009 2:09 pm

psycix wrote:For just a basic gun, I would probably spend less money and time (but time = money) on the commercial factory made QEV then the homemade one.

Sure, but that's why I made the comment about the chrono being a project in and of itself. If your hobby is electronics, it makes sense to make one. If your hobby is NOT electronics... just buy one!

PS: I only make my own valves if there isn't a commercially available option at a reasonable price. If I'm looking at a small bore, low pressure gun? No way do I make one...Not gonna do better than a COTS QEV! ;)
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Unread postAuthor: Technician1002 » Sun Nov 22, 2009 2:23 pm

In my case, I wanted to measure acceleration in the barrel for trimming the barrel to the proper length for a competition. You can't buy a chronograph that will do that for any price.

http://inteltrailblazerschallenge.wikispaces.com/Barrel+length+trim+method

:D
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Unread postAuthor: jeepkahn » Sun Nov 22, 2009 2:55 pm

Technician1002 wrote:In my case, I wanted to measure acceleration in the barrel for trimming the barrel to the proper length for a competition. You can't buy a chronograph that will do that for any price.

http://inteltrailblazerschallenge.wikispaces.com/Barrel+length+trim+method

:D


but you're also an electronics whiz... so for you, homegrown was a project of it's own...
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Unread postAuthor: spudamine » Sun Nov 22, 2009 3:02 pm

There are a lot of examples of people measuring odd speeds which don't agree with GGDT or just seem unfeasibly high, this is often debated at length and gets put down to something like muzzle blast. At least with a home made chrony using a soundcard, you get some real data to look at not just a number. A well made chrony looks to be a much more useful diagnostic tool in such cases than a commercial one, you can look for the signatures of the individual optical gates or even seperate out different objects such as sabots, Not to mention Jimmy's chrony which he used to measure ROF for a BBMG,
Another factor, in countrys where firearms are largely prohibited a commercial chrony is uncommon enough to demand a higher price.
I'm planning on making one soon, have to say I derive as much satisfaction out of making a good set of tools as the cannon itself.
As I'm largely unfamiliar with commercial chrony's could I get one big enough to measure a shot from my hybrid tennis ball cannon?
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Unread postAuthor: D_Hall » Sun Nov 22, 2009 3:32 pm

Technician1002 wrote:In my case, I wanted to measure acceleration in the barrel for trimming the barrel to the proper length for a competition. You can't buy a chronograph that will do that for any price.

http://inteltrailblazerschallenge.wikispaces.com/Barrel+length+trim+method

:D


From a theory perspective, I have one VERY similar to that at the office.

I say from a theory perspective, because the coils aren't mounted on the barrel but are in separate stands. But the idea of a coil-based chrono? Yeah, those are commercially available (and actually, the one I've got has large enough coils that you could physically just put your barrel inside the coils... it's a bit pricey though).


edit again: The one I've got is made by these folks... http://www.physicsapp.com/
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Last edited by D_Hall on Sun Nov 22, 2009 3:36 pm, edited 2 times in total.
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Unread postAuthor: D_Hall » Sun Nov 22, 2009 3:33 pm

spudamine wrote:Not to mention Jimmy's chrony which he used to measure ROF for a BBMG,

While I do get your point when you're discussing odd requirements, I will say that I've seen a commercial chrono that not only would do that, it would provide you with an X,Y coordinate of where your bullet impacted (instead of basic shadow boxes, it used an array of lasers).

As I'm largely unfamiliar with commercial chrony's could I get one big enough to measure a shot from my hybrid tennis ball cannon?

Sure. The F1 mentioned previously in this thread will do it. Cost is $70 US.
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Unread postAuthor: Technician1002 » Sun Nov 22, 2009 8:50 pm

One advantage of magnetic is it is unaffected by dust, mist, or anything that is not the magnet flying through. The accuracy is only as accurate as the measurement of the distance between coils and the sound card crystal clock timebase. A crystal timebase is quite accurate. Mechanical stability of the coil locations is a much larger variable.

You could use the magnetic coils to calibrate the commercial chrony.

I say from a theory perspective, because the coils aren't mounted on the barrel but are in separate stands. But the idea of a coil-based chrono? Yeah, those are commercially available (and actually, the one I've got has large enough coils that you could physically just put your barrel inside the coils... it's a bit pricey though).


How much is a coil of wire with a little RFI shielding, filtering and a zero crossing detector? Audacity is cheaper than a full dedicated interval timer. :D

As far as seperate loops, that can be done. My pickup will work either in active (with a bias magnet) or passive with a launched magnet. The one I used is the passive one they mention, but home built. It didn't cost much as the wire was some old telephone wire. Living in the city, some RF suppression was required. Anyone with basic electronics that can build a low pass filter can cut out RF interferance by making the low pass filter cut out frequencies above 20KHZ (max sample rate). A simple resistor and capacitor does the trick with a cost under a dollar.
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Unread postAuthor: jimmy101 » Mon Nov 23, 2009 3:14 pm

Why build your own? Because to some $70 is a lot, especially for a hobby and when for less than $10 you can build something that is more accurate than a $70 chrony.

How is it more accurate? Because it's operation is observable and understandable. A shooting chrony is a black box. How it is supposed to work and how it actually works is not necessarily the same thing. You can't tell if the Chrony did what it is supposed to do or if there was some problem. You really can't calibrate an F1 type chrony unless you have some very expensive equipment, or a $10 homemade chronometer. :)

ROF is nice. A $70 chrony won't do that.

Not putting a $70 (or much more) piece of equipment nearly in the line of fire is nice. Especially when the gun is homemade and the ammo is a veggie. Ya the round should miss the Chrony but ...

Getting a chrony to work with very small ammo (like an 0.177 bb) can be tricky.

Once the homemade chrony is setup you are 90% of the way to measuring other useful things like pressure and temperature transients in combustion guns, voltage versus time for things like coil guns ... all kinds of interesting stuff.

I'm surprised more coil gunners don't use homebrew chronies. It's pretty easy to get very useful information like velocity and V vs. T. How in the world can you fine tune a coil gun without that info?

Asking "why build your own chrony" is like asking why build a spud gun at all? For $100 you can get a cheapo 0.22 rifle that has the same muzzle KE as a basic spud gun. And you can actually hit a target more than 30' from the muzzle. So what's with the goofy idea of firing veggies out'a piece of plumbing?

Buillding a homebrew chrony is about like a gov't lab deciding they'll build a custom gun from scratch instead of just farming the entire project out to a contractor. ;p
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Voltage versus time (negative transient) and muzzle velocity data (positive transients) for a coil gun, using <$10 worth of parts.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 8:11 pm

jimmy101 wrote:Not putting a $70 (or much more) piece of equipment nearly in the line of fire is nice. Especially when the gun is homemade and the ammo is a veggie. Ya the round should miss the Chrony but ...


It's a rite of passagefor Combro owners :D

Getting a chrony to work with very small ammo (like an 0.177 bb) can be tricky.


No problem with 0.177" BBs with my F1 but still can't get a reading for 3mm bearings from my pen gun. Worked with nail darts of a similar diameter though.

Buillding a homebrew chrony is about like a gov't lab deciding they'll build a custom gun from scratch instead of just farming the entire project out to a contractor. ;p


Touché ;)
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