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Author Topic: Dynamics of a bow stabiliser for archery/board:26-100-  (Read 11458 times)
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johnske
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on: January 13, 2010, 06:29:36 am » posted from:Brisbane,Queensland,Australia

This is my first time here and I would like to request a simulation of the dynamics of a bow (archery) ‘stabiliser’ for a power-point presentation I'm doing as a coaching aid for archers. I would like to treat the motion of the bow and stabiliser as a spring pendulum type motion being viewed from above.

  The bows centre of mass is moved laterally from the equilibrium aiming position by forced vibrations (of 1/10 up to 10 Hz – the 10 Hz vibration may be superposed on the lower frequency) that originate at the shoulder. Rotatory inertia forces the bow to then rotate freely in the hand (it's very lightly frictionally damped). The restoring force for the rotatory component of the motion is a vector component of the bows draw-force that acts to pull the bow in line with the line of force. Overall, this rotatory component of the motion due to inertia and string tension supposedly helps to reduce shooting error by keeping the angle that the bow is pointing away from the target centre at a lesser angle than the angle the line of force is away from the equilibrium position.

Oscillation is initiated by a rather large motion to bring the bow to the equilibrium (aiming) position where it is then halted abruptly. A low frequency arm “wobble” (< 1 Hz) and muscular tremors (~10 Hz) occur soon thereafter - the intent of the stabilisers is to reduce error due to these motions.

Even with sketches the detailed motion is difficult to describe for all circumstances and a Java simulation would be most educative and informative. Some sketches are shown in the attachment.


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Fu-Kwun Hwang
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Reply #1 on: January 13, 2010, 10:20:50 am » posted from:Taipei,T\'ai-pei,Taiwan

I read your article and word document. But I was not able to build a physics model for your case.
Because I do not fully unstand the whole situation.
I tried to search google with keyword "physics of archery", but I can not find similar situation.
To build a simulation we need a model.
I need to find equations for all the forces/torque in the system.
You also have some "forced vibration" , may I know the form of the force or the amplitude and direction of the vibration. 

"The restoring force for the rotatory component of the motion is a vector component of the bows draw-force that acts to pull the bow in line with the line of force. "
But what is the magnitude of the force when it is pointing at different angle (deviate from the line of foce)?
Does the so called "line of force" is a fixed vector or is it going to be changed with time?

I am not familar with archery. I need physics model to generate simulation. Please provide me with detail information or we need to discuss ,and make some assumptions, to build a complete model to simulate it.
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johnske
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Reply #2 on: January 13, 2010, 06:24:50 pm » posted from:Brisbane,Queensland,Australia

I read your article and word document. But I was not able to build a physics model for your case.
Because I do not fully unstand the whole situation.
I tried to search google with keyword "physics of archery", but I can not find similar situation....

Thank you...

I doubt that you will, bow stabilisation has been used since around 1960 but unfortunately, as far as I know no-one has ever fully documented the dynamics of bow stabilisation. This omission inevitably leads to heated arguments among archers, with several fanciful ideas about ‘how stabilisers work’ and the best way to arrange all the various stabiliser masses. I am endeavouring to rectify this omission with this presentation.

I have added some further details in this attachment


* no stabs.gif (27.37 KB, 468x105 - viewed 272 times.)

* with stabs.gif (27.6 KB, 468x105 - viewed 312 times.)

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« Last Edit: January 13, 2010, 06:49:30 pm by johnske » Logged
Fu-Kwun Hwang
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Reply #3 on: January 14, 2010, 09:26:44 pm » posted from:Taipei,T\'ai-pei,Taiwan

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The use of bow stabilizers can greatly increase your accuracy.

Stabilizers will help balance out the weight of your bow and also help reduce the bow movement once the bow is shot.

Most of the stabilizers on the market today can also help reduce vibration and noise, resulting in better shot placement.

I found an article: Modeling and Computer Simulation of Bow Stabilization in the Vertical Plane.

More references are found:
Controlling Bow Behaviour with Stabilisers
Please let me know: Can we use the information/model described in the above articles.

There is another article
Identification of the bow stabilization mechanism by numerical simulation of the laminar asymmetric flow of a viscous incompressible fluid past a cylinder with a projecting disk
at http://www.springerlink.com/content/n331m37568151544/ but I was not able to view it.
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johnske
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Reply #4 on: January 15, 2010, 05:26:10 am » posted from:Brisbane,Queensland,Australia

Code:
The use of bow stabilizers can greatly increase your accuracy.

Stabilizers will help balance out the weight of your bow and also help reduce the bow movement once the bow is shot.

Most of the stabilizers on the market today can also help reduce vibration and noise, resulting in better shot placement.

I found an article: Modeling and Computer Simulation of Bow Stabilization in the Vertical Plane.

More references are found:
Controlling Bow Behaviour with Stabilisers
Please let me know: Can we use the information/model described in the above articles.

There is another article
Identification of the bow stabilization mechanism by numerical simulation of the laminar asymmetric flow of a viscous incompressible fluid past a cylinder with a projecting disk
at http://www.springerlink.com/content/n331m37568151544/ but I was not able to view it.

I have the article by Ellison but have not previously seen the first paper.

While Ellisons approach to the subject is (overall) fairly good, the conclusions he makes are however somewhat biased towards the use of Torque Flight Commpensators (TFCs). TFCs are basically flexible rubber mountings attached to the bow to which the stabiliser rods are mounted and these effectively make the stabiliser rods 'flexible' which, I believe, is what the other author is referring to in his paper on stabilisation using flexible rods in the vertical plane.

TFCs were introduced because it was found the natural 'bendiness' of fairly rigid stabiliser rods tended to kill some of the vibration after the arrow was released and many archers thus thought that the principle function of stabilisers was to kill vibrations. TFCs were thus introduced simply to enhance the vibration damping effect.

however, the rubber mounting effectively negates the ability of the stabiliser masses (on the ends of the stabiliser rods) to resist torque about the vertical axis in a timely manner (there is a delay while the rubber is being compressed) and the rotational inertia of the stabiliser is then effectively isolated. (Ellison does make a small reference to this in his paper)

But the fact is that TFCs are no longer in common use! They are 'old school'. Most top archers now favour using stabiliser rods as rigid as possible, the few that still use rubber to dampen vibration now use very hard rubber "weights" (known as "doinkers") on the outer ends of the stabiliser rods to supplement the mass of the metal stabiliser masses.

Ellison does also make some reference to a conclusion that movement in the horizontal plane is 'under the control of the archer'. This is not quite correct, the ~ 10 Hz muscular tremor is a natural muscular function that simply cannot be controlled, likewise, the natural frequency of rotation of the bow (~ 1-2 Hz) about a vertical axis cannot be controlled by the archer while aiming, there is a (roughly) one second delay between perception of a wobble and the archers response to control the wobble.

After moving the bow to an aiming position the natural frequency of the bow sets it oscillating slightly, this motion is damped after 2 to 3 seconds by small frictional forces between the archers bow-hand and the bow-grip (the bow sits loosely in the "V" between thumb and forefinger and it is not "gripped"). The sight extends out past the bow and the archer sees this oscillation as a left-right motion "of the bow" - if they do not wait for friction to act and attempt to control the motion themselves they inevitably make things worse by introducing a "wobble".

We are only looking at motion in the horizontal plane at this point in time
« Last Edit: January 15, 2010, 05:28:54 am by johnske » Logged
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Reply #5 on: February 02, 2010, 10:05:09 am » posted from:Taipei,T\'ai-pei,Taiwan

A model is required if I want to create a simulation.
I was not able to build a model for your case just by reading those articles.
Could you provide me a complete model  about a bow stabiliser for archery so that I can try to build a simulation base on the model.
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