Natural release mechanics

Hanare (離れ, ばなれ, 離=detach, separation) – release.

Good hanare should be natural, meaning that it is not done consciously by opening the hand. Instead it should occur on it’s own, out of nowhere, surprising the shooter. The reason behind this is that the release should happen at the point of highest tension; releasing consciously results in the body “preparing” for the recoil from the release, by reducing the tension just before the release, and going “limp” during the release.

There seem to be a lot of mystery around the release. There are a lot of visualizations used as the explanation, like “drop of dew detaching from the leaf”, “snow falling from the tree branch under its own weight”, and so on. But the mechanics of the natural release are not really explained (at least not in English literature that I have access to).

Let’s investigate what is happening at that mysterious moment.

Release occurs because the thumb of the right hand is opened by the string; index and middle fingers hold the thumb in place, and when they let the thumb go, it opens and releases the string. The point of contact is here:

Image result for torikake

(http://bernardkyo.pixnet.net/blog/post/175793757-%E7%BA%8C%E8%AB%87%E3%80%8C%E5%8F%96%E6%87%B8%E3%81%91%E3%80%8D)

The thumb is very hard, it is like a pipe, so it doesn’t bend. Therefore the contact between the middle finger and the tip of the thumb can be simplified to a single point (to make the analysis easier). You can see on this old glove where it is worn the most:

Image result for kyudo string grip glove

(http://gaijinexplorer.blogspot.ie/2012/11/the-nightmare-kake.html)

Pushing the bow while simultaneously pulling the string in the opposite direction results in bending the bow. As the bow bends, the force required to bend it increases. Therefore the deeper the draw, the higher the force. These two forces meet in the point of contact between the string (that is being bulled to the left by the bow) and the groove on the glove (that is being pulled to the right by the right elbow). If these forces would be represented as vectors, they would be on the same line (that is the line of the arrow) but with opposite directions. Because the whole set up doesn’t move to the left or right, these forces balance out / cancel out each other.

But then why would the thumb open to the side, if these forces are parallel? What is pushing it to open up, and also, what is holding it in place? There has to be some additional force pulling it to the side.

Looking closer at the point of contact between the string and the glove, there is a special grove for the string to sit in. While the thumb is closed, the string can’t escape. When the thumb opens, the string can slide out.

The key to keeping the thumb closed is the static friction in the point of contact between the middle finger and the glove. Learning, and managing, that static friction, is the gateway to natural release. It requires a lot of practice to understand what’s happening there, and it also requires the glove to be conditioned (or aged) sufficiently with the key ingredient – giriko powder.

Giriko is responsible for increasing and maintaining the static friction in the point of contact between the top of the thumb and bottom of the middle finger. The more giriko the higher the static friction. Why is static friction so important? Because instead of gripping the thumb using muscles / fingers, it can be constrained by the static friction in the point of contact.

Static friction can be represented on a graph:

(https://en.wikipedia.org/wiki/Friction)

You can see that the static friction is greater than kinetic / “dynamic” friction.
There is also a point where the static friction changes into the kinetic friction – at this point (which is the peak force on the graph above) the object begins to move (relative to the other object). In terms of the thumb / middle finger interaction, it is the point where the thumb slides out from under the finger, thus opening up and releasing the string.

Static friction value depends on three parameters (as per Wiki):

“Dry friction is governed by the model:
{\displaystyle F_{\mathrm {f} }\leq \mu F_{\mathrm {n} },}
where:

F_{\mathrm {f} }\,is the force of friction exerted by each surface on the other. It is parallel to the surface, in a direction opposite to the net applied force.
\mu \, is the coefficient of friction, which is an empirical property of the contacting materials,
F_{\mathrm {n} }\,is the normal force exerted by each surface on the other, directed perpendicular (normal) to the surface.”

(https://en.wikipedia.org/wiki/Friction)

Giriko is responsible for increasing the coefficient friction. Glove without giriko has low value of coefficient of friction, meaning that the static friction is lower / easier to overcome.

The model also suggests that the higher the force that is pushing the two surfaces together, the higher the friction between them. So to increase the friction, either change the parameter for coefficient, or increase the “clamping” force between the surfaces, or both.

How does this model look like in the glove under tension?

The string sits in a grove (called tsuru makura) in the base of the thumb:

弦枕

(http://ecoecoman.com/kyudo/dictionary/320_tsuru_makura.html)

Image result for tsuru makura kyudo

(http://www.kyudo.dk/english/apply-resin-to-a-yugake)

When the thumb is closed, this grove keeps the string from flying out.
Picture1.png

(https://www.youtube.com/watch?v=bfxpIDKOujw)

Capture.PNG

Closed thumb vs. the moment just before the release of string:

(https://www.youtube.com/watch?v=akCIcCZs3ZI)

The movement of the thumb is very slight, less than 1 cm, but that’s enough for the string to slip out of the grove.

Forces can be represented graphically as vectors. Let’s map the forces that occur in the glove during the draw:

Picture4.png

Point A – the grove on the glove, where the string sits. This is also the point where the two main forces (push to the left, navy blue arrow; and pull to the right, blue-green arrow) meet.

Point B – axis of rotation of the thumb. This is important as the main forces are not applied to the middle of the thumb; they are applied to the side of the thumb, where the grove for the string is. As a result, under the tension, the thumb “wants to rotate out” (as per the red arrow coming from point A). This is the force responsible for the thumb opening to the side.

Point C – contact point between the thumb and the middle finger. This is where the static friction is generated (orange arrow). This is the “locking mechanism” that prevents the thumb from opening. Because of the axis of rotation, the opening force in point C (red arrow) is smaller than the original opening force in point A (red arrow), so it requires less force to constrain the thumb at point C than at point A.

The force (generated by the bow being bent) applied to the string (and therefore to the glove) changes, and is at it’s peak in the full draw. This force translates to the static friction; what it means is that it’s possible to use very little “muscle generated” force to hold the thumb in place, and instead rely on the static friction.

The thumb is pulled open by the string. As the shooting form progresses, the tension on the string/thumb increases. The greatest tension is at the point of biggest draw, which is in full kai (to be precise, in full kai there is an expansion to the left and right, tsumeai, which increases the draw length even more, until release.

Picture5.png

During the steps of drawing the bow, the static friction changes. Starting from the left, at the first stage the string is only at a slight tension. Therefore the static friction is also low (the height of the graph is small). As the thumb wants to rotate out, the bigger the force that tries to pull out the string, the bigger the force that tries to rotate the thumb. Because the middle finger is perpendicular to the thumb (in the point of contact), it can’t follow the thumb on the opening movement, and it keeps it in place.

On the second image from the left, the tension is slightly bigger, as the archer applies a “pre-tension” while raising the bow. The static friction is therefore slightly higher, because the thumb wants to “escape” more.

On the third image, the bow is drawing to a half, the static friction is much higher, and also closer to the point of release. At this point, if the glove has enough giriko, archer can start to reduce the muscle tension for holding the thumb, and start relying more on the static friction to keep the thumb in place. Again, the bigger the force behind the thumb rotation, the higher the static friction, so as the draw gets deeper, the friction goes up.

On the last image, the bow is fully drawn, the static friction is almost on the point of transitioning to kinetic friction (release). Still, the thumb is held in place, and the string is not released.

The release from that state can be achieved by the expansion of the body to the left and right (tsumeai), and as “the straw that brakes the camel’s back”, this barely visible movement ends up in a dramatic result – a clean, natural release, when the static friction finally gets beaten, and the thumb slides out from under the middle finger.

Now, the biggest problem with this set up is that the force that tries to open the thumb is relatively small. It is easy to apply too much force using the fingers’ muscles, in which case the thumb will never open, no matter how hard you draw / pull. This is when you reach your absolute tension and the string is not released, so you have to consciously open up the two fingers locking the thumb. That is not the natural release, and all bad things mentioned earlier occur.

So there you have it – a very delicate balance of forces, that hold everything in place if executed properly and carefully, and that allow for the natural release.

On two condition though:

1- that there are no other forces interfering with this setup. So for example, if the archer tries to hold the thumb with hand muscles too much, as if there was no static friction in place, this balance is disturbed. I have been doing this from the beginning, especially after I got hit with the string jumping out of the groove mid-draw. I thought that the thumb needs to be held in place by contracting the muscles that pull the middle finger in. In that set up the only way to release the string is to relax these muscles, and that means that the release is conscious.

2- that the static friction is high enough to be able to hold the thumb in place. Part of the problem that I had with the mid-draw unintentional release was that the glove was brand new, so it didn’t have enough giriko embedded in it. As a result the static friction was very low, because it was a friction between deer skin on the thumb and deer skin on the middle finger. Giriko is a powdered resin, so it is the same stuff that is used to cover violin bow. Also the mechanism for generating the sound from violin is based on the static friction – the violin bow pulls the sting on the violin until the static friction is beaten, the the string is released and starts to vibrate (generating sound waves); in the mean time the violin bow pulls the string again, and so on.

After almost 2 years of shooting, giriko is now embedded in the deer skin of the glove. When I pull the thumb by hand from under the middle finger, there is a screeching sound coming from the static friction being broken repeatedly. I think “giriko” name comes from the Japanese vocal expression for that sound, “giri-giri”.

 

 

This changes the shooting experience significantly. I can feel how the string tries to pull the glove off from the hand; if it wasn’t for the tie around the wrist the glove would fall off. There is a feeling of only two points being involved in the shot – the base of the thumb in the left hand (pushing the bow), and the grove in the glove (pulling the string). The draw force connects these two points, and on the vector of the force lies the arrow. The natural release happens so fast that the body can’t prepare for it, as a result it occurs at the highest tension, so the opening of the body to the left and right is natural, powerful and complete. Also the tenouchi works much better, the left hand does not get “limp” just before / after release, left thumb is pushing into the target naturally, as I try to get some extra millimeters of draw length. The bow then spins nicely in the hand every time, and it doesn’t fall down. Somehow the accuracy is also improved, I have no explanation for it yet. But the best improvement is that the shot feels great. There is power, there is intent, there is (some) quality. It is still crude, I can feel that the shooting is far from polished and fully controlled, but I think I’m on the right path. When the shot is guided by the rhythm of deep, slow, abdominal breathing, and the body form (and concentration) is maintained, it really is quite an experience.

The weather is getting better every day, so I’m looking forward to many shooting sessions to investigate and learn more.

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2 thoughts on “Natural release mechanics

    1. I can’t thank you enough for your thoughts and descriptions. Several pieces of information from several sources inside me just clicked together like pieces of a puzzle.

      Like

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