Chronograph ?

[Stick Bender]

Hi everybody  I find myself building more & more sinew bows & exspermenting with different amounts of sinew and lengths of bows so I thought I would pick up a Chronograph to exsperment ,does any body have any recommendation ?

[joachimM]

If you're not particularly interested in exact speed and wanna wait spending 120 USD, you could try the sound-based apps for smartphones or tablets.
It's easy to get exaggerated readings (on both sides), but if it's your intention to compare bows relative to one another this might do the trick, as they can be very consistent.

There are some tests on youtube that compare these apps to regular chronographs, which indicate they are capable of getting very close to readings given by traditional archery chronographs, if you get the settings very right and know how to use them.

the principle of sound-based chronography is explained here http://arxiv.org/ftp/physics/papers/0601/0601102.pdf

[Badger]

   Bow speeds are so close as it is that anything less than accuracy is worthless.

[bradsmith2010]

I have a pro chrono, and my friend has one the same,, they seem to work pretty well and mine has lasted at least 10 years,, it is a very useful tool to develop your bow making skills,,  for example ,, if you are using the mass theory,, you can shoot a bow that has too much mass,, then remove wood as needed, and the chrono,, will show you that the reduced mass in the bow has increased the cast,,, you can also do this with distance shooting,,,but the chrono is more convenient most the time,,

[joachimM]

I know where you're coming from, and the more accuracy the better. But unless you shoot with a shooting machine and exactly parallel to the plane of the sensors of the chrono (instead of at a slight angle, what I often see), exact figures of bow performance seem hard to obtain even with a crystal-based chronograph.
Arrow paradox during flight is another variable that could affect the accuracy of arrow speed estimation (unlike the straight path a bullet follows). The first sensor may be activated during a downward movement and the second during an upward movement, adding error to the calculated speed.

Even these chronographs will easily differ 1-2 fps from each other. Calibration of the crystals is key, but at the end of the day you don't know how accurate your reading was. You may have had a very consistent reading though. Isn't that what it's all about when comparing bows?

I'm pretty certain the inconsistency of release by the average archer gives much more error to the estimate of (relative) bow performance than the method used, even for F1 Chrony or Pro Chrono
 
Sound-based chronography as in the mentioned paper, especially when shooting through paper sheets (to get clean and crisp sound bursts) can be pretty accurate too (recording at 48 khz will give you that), or can at least be very consistent (more consistent than my shooting at least  I don't know how well these apps implement all the variables in this paper (such as changing speed of sound with temperature), but in principle it's feasible.

[bradsmith2010]

joachimM,, very good point,, I still find I can usually tell the shots that are not consistent,, I usually get some duplicates and go with the readings in that range,,,it is not perfect,, but still a useful tool,, it will even make your release better as you practice shooting through the chrono,, sometime I am getting 150 fps ,, then it will read 200,, well I would like to believe that,, but I know the duplicate readings of 150 are probably more reasonable,, with practice you can shoot pretty parallel,, and get a good idea of what a bow is doing,, I find it most valuable while tillering,, when a bow starts to shoot well for its draw weight, I can stop there,, even though I may have started with a longer draw in mind,, hitting the sweet spot for me is more important than going to a preconceived draw in some bow,, I think it is a great tool,, not perfect but very informative when used in the right application,,   

[crooketarrow]

 Your release can had or take away FPS. At a time I hadI've shot other peoples bows and shot faster than they did. ONE RECURVE I SHOT 16 SECONDS FASTER.W IT HIS OWN BOW. On average I out shot most people FPS.

  Your release adds or takes away lots of your bows preformest.

 

[Badger]

As Brad said Joiquin all good points. You can do need to set the angle of the chrono to match your shot angle. You can train yourself to release amazingly accurate. consistently to within 1 fps.

[PlanB]

I have a Chrony, but just as a point of interest Joachim, have used sound to determine the speed of engines using the same method, only capturing the audio from a playback on my laptop from a digital video taken with a simple pocket camera.

I used a downloadable free o-scope application called Visual Analyzer. The videos don't have to be your own for this to work, by the way, you can time all sorts of motor, etc. events from online videos, just play them back and capture through that VA application (or something similar).

The criticism of crystal frequency would, btw, apply not only to chronographs but also to any computer, Ipad, etc. using a sound app to measure speed -- since they use crystals as well to drive the microprocessor and bus.

Also an arrow slows on the way to a target, so the two different devices measure two different things -- initial, and average velocity over the distance involved. Well nothing is perfect!

On a practical basis, I don't think I'll be giving up the convenience of the new Chrony. But it might be interesting to check a second mesurement source once in awhile. And if I had just a shooting video I wanted to check for speed, it's possible to do after the shooting session. You do need to know the accurate distance to a target, of course.

[DC]

Do all chronos come with the same size sweet spot? With my ChronyF1 you have to get the arrow through two "holes" that are about 1"x 3". I'm wondering if other makes have larger "holes"? Also on the Chrony the wires that hold the sun shades plug into the plastic boxes that hold the sensors. If you hit the wires the plastic boxes disassemble themselves Fortuneatly mine just snapped back together. When I'm using it now I don't use the wires or the shades.

[mikekeswick]

F1 chrony is my tool of choice.

[Dakota Kid]

You can build one. Wrap speaker wire around a cut out circle from a 5 gal bucket wall. Wrap it like 20-30 times. Make two of these. Wire them together in series then to a 1/8 mic jack. Space out the two circles 1-2 feet and nail them to a 2 x 4. These coils basically will act like a metal detector producing an electric signal that most sound programs will pick up if you plug it into your computer's mic jack. You should get two distinct spikes as the field point passes through the coils. A few moderate math calculations later you'll have a decent measurement of flight speed. You need to have metal on the arrow or you won't get a reading. Small rare earth magnets will give you an even better reading than metal.

I have yet to finish building mine, but in theory it should do the trick. It seemed to work okay for the guy who wrote the tutorial I read.

[bradsmith2010]

wow thats really cool, but way out of my skill range for sure,, but sounds very interesting,,

[Stick Bender]

Im looking at one at Bass Pro its made by Caldwell it has a audio jack for Iphone & app, Im  guessing its for cross referencing the audio & magnetic field  for a more accurate reading , I would imagine that would be preety accurate.

[PlanB]

That's pretty cool Dakota!