# DIY Bow Chrono



## Smoknnca (Sep 13, 2011)

Very interested. I know I want to build one.


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## dbeaven (Jan 10, 2013)

Mounted the chrono to my bow after work. Still working on the design for the next iteration with a PC board to tie it all together. Probably be a week or so.


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## Clarktar (Mar 1, 2011)

I want to know how to build the 3D printer!!



dbeaven said:


> Mounted the chrono to my bow after work. Still working on the design for the next iteration with a PC board to tie it all together. Probably be a week or so.


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## dbeaven (Jan 10, 2013)

Everything you want to know about building 3D printers: http://www.reprap.org/wiki/Main_Page


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## Clarktar (Mar 1, 2011)

Yea I was checking that out yesterday. Pretty awesome. I wish I had the money for a Kit.... Would be really really fun!

I am super interested in your chrono. If you could build me the Red piece, I think I could buy the electronics and fiddle with that part on my own....

I think this is the coolest DIY I have seen in a long time.


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## Clarktar (Mar 1, 2011)

I would pay you to print a ReRap for me....  Please!


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## NJlungbuster (Sep 14, 2006)

How Much??? lol


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## Triggins (Aug 30, 2012)

That is awesome! I want to see the final product..!


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## dbeaven (Jan 10, 2013)

I could print the current design for you, it keeps changing and improving though. Takes about 3 hours to print. PM me if you're interested. I'd need some $$ to pay for the filament and shipping though. And can't guarantee how quickly I could get it to you. It's time consuming; and I still need my printer to be available for my other projects. 

If you're looking for Reprap parts, ebay is decent. People sell kits. I'm saving up for some aluminum extrusions to build a bigger one so I can make pieces form fit to my carbon matrix for a bow press. Using the Xbox Kinect as a 3D scanner 

Hopefully this weekend I'll have time to put up more info and the latest iteration.


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## NJlungbuster (Sep 14, 2006)

As long as the current model works and is accurate, i'd pay some cash to get one to try out. Oh and I went and checked out that link. I have a headache now lol. Thats too smart for me.


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## dbeaven (Jan 10, 2013)

The one in the video isn't as accurate as I want, the IR LEDs I have on it aren't the right ones. I'm going to put some other ones on and try it out. If that fixes the problem, NJlungbuster can try it out and give me some feedback. I'd have to charge the cost for parts and shipping though, so I can buy more parts for the next ones I plan on making.


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## NJlungbuster (Sep 14, 2006)

Yeah let me know and I'll be happy to try it out.


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## dbeaven (Jan 10, 2013)

Tried the new IR LEDs, they helped but the signal when the arrow crosses is a little too slow for an accurate read on FPS. I'm going to have to scrap the current design so I can fit more components (op-amps) to make a nice crisp signal to the microprocessor so it can time it within 4uS, which is about +/- 1.8 feet per second error. 

I've got a couple people so far that are willing to test them out for me, im just going to charge for shipping and parts on these so that I can buy more parts for the next one(s). The next set I build, I'll have them give me some feedback.


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## sawicki4x4 (Jan 2, 2013)

3D Printers are fun. But expensive i think the cheapest one you can buy is $1400 or around there. But iv got one in class i can play with. Gotta love solid works


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## sawicki4x4 (Jan 2, 2013)

dbeaven said:


> Tried the new IR LEDs, they helped but the signal when the arrow crosses is a little too slow for an accurate read on FPS. I'm going to have to scrap the current design so I can fit more components (op-amps) to make a nice crisp signal to the microprocessor so it can time it within 4uS, which is about +/- 1.8 feet per second error.
> 
> I've got a couple people so far that are willing to test them out for me, im just going to charge for shipping and parts on these so that I can buy more parts for the next one(s). The next set I build, I'll have them give me some feedback.


If you want someone to try one out id be more then willing to pay for the parts and shipping.


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## Mikenmel08 (Aug 9, 2011)

I would buy one..


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## dbeaven (Jan 10, 2013)

Not supposed to talk about selling these in the DIY section. But once I get the design tweaked in I plan on selling them. In the meantime, here's the schematic I made to clean things up. Just have to lay it out and get it fabbed by Sunstone circuits.


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## sawicki4x4 (Jan 2, 2013)

Looks good. how much they costing you to build.


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## dbeaven (Jan 10, 2013)

Still alot of unknowns without the final one built yet, but somewhere around $40-50 as is.


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## Mikenmel08 (Aug 9, 2011)

Have this funny feeling you are going to be a very wealthy person:thumbup:


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## dbeaven (Jan 10, 2013)

Mikenmel08, I can hope - maybe one day


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## Mikenmel08 (Aug 9, 2011)

I would most definitely be interested in one...


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## Veni Vidi Vici (Jan 23, 2011)

dbeaven said:


> Mikenmel08, I can hope - maybe one day



Have you heard about www.kickstarter.com? It's a way to raise funds for a project or business.

I heard about it in this article: http://www.luminous-landscape.com/essays/self_publishing_a_landscape_photography_book.shtml


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## Don Schultz (Jul 5, 2002)

Fabulous work. I had no idea one could build a 3D printer from a kit. I am mildly surprised you are having signal level problems. I am guessing the arrow is breaking an IR thrubeam.

I am less enthusiastic about the chrony itself. An issue I see with the design theory is that the arrow is accelerating very hard for the majority of the time it is in the chrony's sensors, with some deceleration during the 2nd 1/2 of the arrow's period in the sensor as it comes off the string. So the velocity of the arrow is constantly changing by gross amounts all the time it is in the sensor. 

While I don't doubt the indicated velocity could be related to the velocity measurements of conventional "off the bow" chronographs for a given bow/arrow combination, it seems that your bow mounted chrony may need to be calibrated against a conventional chrony for each bow/arrow combination. So the usefulness of the device is somewhat in question for me.

I assume you are entering an arrow length factor into the software application already.


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## dbeaven (Jan 10, 2013)

Once I get my op-amp circuit put together I plan on comparing it to a calibrated chrono. The length of the arrow isn't needed. The distance between sensors and time it takes to trip them is whats used to calculate the FPS. The force curve for an arrow launched from any bow is relatively flat. The acceleration therefore is linear. 








Depending on the results, it may be so negligible that it wont matter much. There is a current x-band based chrono that measures the arrow as it leave the bow also and requires no additional information to compensate for the acceleration. 

So here's hoping.

Here's some good data a group got on arrow acceleration profiles. There's a ton more info on google....

http://www.gcdataconcepts.com/arrow.html


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## Veni Vidi Vici (Jan 23, 2011)

dbeaven said:


> Once I get my op-amp circuit put together I plan on comparing it to a calibrated chrono. The length of the arrow isn't needed. The distance between sensors and time it takes to trip them is whats used to calculate the FPS. *The force curve for an arrow launched from any bow is relatively flat. The acceleration therefore is linear. *


This is not true. There is no bow that has a flat force/draw curve. At best, a long bow has one that is very close to a straight line, but it is not flat, increasing constantly from brace to full draw.

Here's a good summary of force curves. http://arrowtrademagazine.com/articles/nov_06/ForceDrawCurves-November 2006.pdf

Also, I think the x-band chrono you referred to works on a Doppler shift principle, which is different than timing between two gates.

If you could have your chrono "arm" itself upon first detection of the arrow tip, then start timing as soon as the nock completely clears the rear sensor and stop timing when the nock completely clears the front sensor, you would then be measuring a single point on the arrow after it has completely left all influences from the bow.


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## dbeaven (Jan 10, 2013)

I was referring to release force. Not draw. I said relatively flat, meaning the acceleration slope is linear. Once I get the chrono, I'll see how much of a difference it makes. But I understand where you're coming from.

The x-band chrono is doppler shift, but in a gated mode. It simply measures the presence of the arrow between xband receiver 1 and 2 with known difference. The 10ghz antennas are slit horns. 

At the moment it measures the time between breaking gate 1 to gate 2 which is 2 inches apart. This eliminates the need for putting in the length of each arrow used. But, I can see how the nock might address the issue of arrow acceleration after it crosses the second gate. If that acceleration is significant, I'll have to change my approach. If not, ill keep the current design. I'd prefer it to be as simple as possible.


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## dbeaven (Jan 10, 2013)

Oops, you're totally right. Don't read posts while at work. The force changes with displacement. The arrow will not be at full speed when it crosses the second gate. It will be significant considering the draw curve of a compound bow. 

I've got to change my method, to measure the arrow once its out of the power stroke. Damn. Might need a little reflective sticker for the nocks... Wanted to make this simple..


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