SHOOTING MACHINE

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greybeard
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SHOOTING MACHINE

#1 Post by greybeard » Thu Oct 11, 2018 2:55 pm

I needed to build a shooting machine to generate the data to help a university undergraduate complete a paper.

With a little effort and a few dollars I was able to modify my force/draw setup viewtopic.php?f=34&t=11983 to a shooting machine.
I purchased a release aid on special for $23.00 which I could modify, the release aid enabling a consistent ‘clean’ loose.
To my surprise the shooting machine worked perfectly on the first test run.

A recurve and longbow each being 45lb@28” were used for the test once their stored energy was established.

Typically arrow velocity varied by .3% i.e. Red arrow longbow, 162.4, 162.6, 162.2 fps. Red arrow recurve, 174.5, 174.7, 174.2 fps. Stated accuracy of the chronograph was within .5%. The base for the shooting machine was a little unstable which may have added to the variations in velocity.

The chart below illustrates the fact that different arrow mass will have little impact on the efficiency value within the bow even though arrow velocity increases.
Although this fact has been accepted for many years it is rewarding to go through the process to verify it.
Bow Test.jpg
Bow Test.jpg (179.88 KiB) Viewed 741 times
Once a bowyer has this information he / she can make changes to limb design / configuration to make efficiency improvements.

I believe the longbow utilising a rock maple and black wattle core could be improved by shortening the n to n length to 68” resulting in a lower limb mass and increased limb recovery speed.

The following image is for a 40# longbow utilising a laminated bamboo core.
40 lb Longbow Efficiency With Chrony.jpg
40 lb Longbow Efficiency With Chrony.jpg (88.48 KiB) Viewed 741 times
Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

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Stickbow Hunter
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Re: SHOOTING MACHINE

#2 Post by Stickbow Hunter » Wed Oct 17, 2018 11:13 am

Crunching the numbers can be very interesting. I did a lot of bow testing back in the early 1990's with Grant McDonald. We never used a shooting machine but in those days I had a very consistent release with only 1 fps variance usually.

Jeff

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greybeard
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Re: SHOOTING MACHINE

#3 Post by greybeard » Tue Oct 23, 2018 3:20 pm

Jeff,

Some years back my release was fairly consistent but after several rounds of Dupuytren's contracture surgery and the onset of arthritis it has gone downhill.

Maintaining a consistent anchor point has become more difficult as time passes hence the necessity for the shooting machine.

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

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Stickbow Hunter
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Location: Maryborough Queensland

Re: SHOOTING MACHINE

#4 Post by Stickbow Hunter » Tue Oct 23, 2018 5:36 pm

greybeard wrote:
Tue Oct 23, 2018 3:20 pm
Jeff,

Some years back my release was fairly consistent but after several rounds of Dupuytren's contracture surgery and the onset of arthritis it has gone downhill.

Maintaining a consistent anchor point has become more difficult as time passes hence the necessity for the shooting machine.

Daryl.
Fully understand that Daryl; these days I would most certainly need a shooting machine also. It's a pain growing old.

Jeff

subseapeter
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Re: SHOOTING MACHINE

#5 Post by subseapeter » Wed Oct 24, 2018 1:26 pm

Very interesting. Did you manage to capture any video of the machine in use?

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greybeard
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Re: SHOOTING MACHINE

#6 Post by greybeard » Thu Oct 25, 2018 11:05 am

Hi Peter,

Unfortunately I do not have suitable facilities to take video clips.

I copied the design below as it appeared to be more suitable with the bow mounted horizontally rather than vertically particularly when testing a 70” n to n longbow.
Shooting Machine.jpg
Shooting Machine.jpg (44.52 KiB) Viewed 614 times
Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

User avatar
greybeard
Posts: 2805
Joined: Tue Feb 07, 2006 9:11 am
Location: Logan City QLD

Re: SHOOTING MACHINE

#7 Post by greybeard » Wed Apr 03, 2019 4:43 pm

I finally got some photos of the shooting machine.
Shooting Machine Comp.jpg
Shooting Machine Comp.jpg (203.08 KiB) Viewed 294 times
It was rewarding to hear that the student [Ben] gained the highest possible marks for his paper [Perspectives in Physics Research: The Efficiency of the Traditional Bow.]

Coincidentally, the author of one of the many papers that I gave Ben to help with his research happened to be that of his lecturer. [The Asian war bow by Timo A. Nieminen]

Daryl.
"And you must not stick for a groat or twelvepence more than another man would give, if it be a good bow.
For a good bow twice paid for, is better than an ill bow once broken.
[Ascham]

“If a cluttered desk is a sign of a cluttered mind, of what, then, is an empty desk a sign?” [Einstein]

I am old enough to make my own decisions....Just not young enough to remember what I decided!....

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