High gear/low gear

[willie]

Thought experiment: Applying arrow paradox to bow limbs on release. The most motivated part of a bows limb will move first and may move faster than the limbs tips. This loads the other parts of the limbs with energy until all energy is spread equally across the limb. Under slow motion, it probably looks like a wave. If the timing of this wave could be done correctly, the tips would be be at tje crest right when brace heightis hit, snapping the last of the energy into the arrow.

I can see it looking like a wave if it is jim hamms turtle bow in TBB, but we always go with  tips as light as practical in real life

[willie]

good videos Pat.
going to .25 speed it looks like any part of the limb getting ahead of any other part only happens after the arrow is gone

[Tuomo]

Bow: 36#@27"

200 grain arrow: https ://www.youtube.com/watch?v=izv2y9qgJ8g
1100 grain arrow: https ://www.youtube.com/watch?v=Y4JCD2_O5uI

No difference in bending of the limb.

It is all about efficiency - string, arrow and limbs are moving as a one moving part. The bow is storing certain amount of potential energy, which depends on many things - and hysteresis is one of the most important factor in wooden bows. As Steve said earlier, a bow which is the most energy efficient, is the fastest bow: "the fastest bow with any arrow will usually stay the fastest regardless of arrow weight".

[Marc St Louis]

Bow: 36#@27"

200 grain arrow: https ://www.youtube.com/watch?v=izv2y9qgJ8g
1100 grain arrow: https ://www.youtube.com/watch?v=Y4JCD2_O5uI

No difference in bending of the limb.

It is all about efficiency - string, arrow and limbs are moving as a one moving part. The bow is storing certain amount of potential energy, which depends on many things - and hysteresis is one of the most important factor in wooden bows. As Steve said earlier, a bow which is the most energy efficient, is the fastest bow: "the fastest bow with any arrow will usually stay the fastest regardless of arrow weight".

No difference in limb bending but big difference in limb vibration

[avcase]

I always figured a low gear design is one that simply lacks “high gears”.  It is one of those bows that is said to “like heavy arrows”.

A straight bow with zero brace height and long flexible limbs could be considered the ultimate low gear bow. The bow stores lots of energy in the draw, but the limbs won’t be able to get out of their own way fast enough when shot. The archer would almost be better off throwing the arrow!

For maximum efficiency, the ideal situation is where all parts of the bow return along the same path as when drawn.  When a bow shoots a very heavy arrow, this is approximately what is happening and efficiency is relatively high.  If the design can maintain this for very light arrows without additional waves of limb distortion or vibration, then the light arrow efficiency will also be very high. There would also be little visible difference in post-shot vibration on the high speed video between the heavy and light arrow.

Alan

[willie]

No difference in limb bending but big difference in limb vibration

Marc, are you writing of limb vibration before or after the bow reaches brace upon release?

If the design can maintain this for very light arrows without additional waves of limb distortion or vibration, then the light arrow efficiency will also be very high. There would also be little visible difference in post-shot vibration on the high speed video between the heavy and light arrow.

Alan, you seem to be specific about limb distortion (from the path along which it is drawn) occurring between FD and brace on the powerstroke. Has this been observed photographically? Toumo sees no difference in his two videos, but of course, that is one specific bow used with two different arrows.

[Selfbowman]

I don't know about gears in a bow! But if a bow has shock wethere from bow vibration or string related it ant good. That robs cast! We all ways won't to see full draw pics? To prove even limbs. Well if the bow goes back to brace even it won't have much shock! If the limb tips are narrow as possible the less the shock. Reflex adds shock is what I have noticed. But it transfers more energy to a point. To much reflex adds to much mass which will add shock. I pay more attention to the shock in the bow.
Set is the other enemy! I think it comes down to design where the bow is light on the ends has little shock , limbs come to rest evenly , and have a good force draw. Then you have to match a good arrow that flys straight and true. I guess I am in agreement with Alan . Lol
Arvin

[avcase]

Alan, you seem to be specific about limb distortion (from the path along which it is drawn) occurring between FD and brace on the powerstroke. Has this been observed photographically? Toumo sees no difference in his two videos, but of course, that is one specific bow used with two different arrows.

I have not accurately measured these limb vibrations photographically. I can pretty clearly see the symptoms post shot and measured the effect on efficiency. If I were to do it photographically, then I would mark the side of the bow with about 20 dots from the center of the riser to one of the limb tips. I’d start with the bow braced, then track the limb as it is drawn. Then I’d need to have pretty clear high speed video, around 5000-10000 frames per second, to track the return path of the limb during the shot.  It would be an interesting exercise.

This is much easier to do with a computer model however.

Alan

Alan

[Tuomo]

For maximum efficiency, the ideal situation is where all parts of the bow return along the same path as when drawn.  When a bow shoots a very heavy arrow, this is approximately what is happening and efficiency is relatively high.  If the design can maintain this for very light arrows without additional waves of limb distortion or vibration, then the light arrow efficiency will also be very high.

Solution: Rigid limbs. As Steve has said - minimize bending portion of the limb. Just like Turkish flight bows...

[Badger]

  I made what I called a hinge bow several years ago with very extreme recurves and reflex, something like 12". The bow was about 4" wide in the bending area which I think was no more than about 8" long up close to the handle. It broke down quickly because of set and hysterisis but in the initial shots it was the fastest bow I had ever seen bar none with a 10 grain per pound arrow. I think it was like 212 fps on the first shot. And dropped with every shot until it stabilized after about a dozen shots. Once it stabilized it had no real performance left but it did confirm what is possible if the right materials were used. Short working areas solve a multitude of design problems with bows. The stored energy was over 125% of peak draw force. 

[DC]

What was it made of?

[sleek]

  I made what I called a hinge bow several years ago with very extreme recurves and reflex, something like 12". The bow was about 4" wide in the bending area which I think was no more than about 8" long up close to the handle. It broke down quickly because of set and hysterisis but in the initial shots it was the fastest bow I had ever seen bar none with a 10 grain per pound arrow. I think it was like 212 fps on the first shot. And dropped with every shot until it stabilized after about a dozen shots. Once it stabilized it had no real performance left but it did confirm what is possible if the right materials were used. Short working areas solve a multitude of design problems with bows. The stored energy was over 125% of peak draw force.

I remember this bow. It was Osage. Steve, you are the only guy to break 200 fps at 10gpp, and hardly anybody even knows it. I think about that design often, trying to figure out how to stop the  losses you encountered, then use that in my own short bow design. Probably won't ever hit 200 fps, but i want steady 180s, consistantly between bows. Im close. That bow was insane to see on your thread.

[maitus]

I think the limbs will move back exactly the same way as they are pulled back. You can do it slow, moving your hand back from full draw, or fast, relise. The speed depends just from arrow weight. My understanding of gearing is ratio between pulling the limbs back ( straight limb bow) and pushing them together vertically (5 curve bow). If to think, why braced bow have bigger string tension than full drawn bow....and why stringig a bow is easier with bending the limbs, than pressing the tips together (like kids bow), it could explane something.
Its hard to explain what i think in foreign  language but i hope you get what i mean .

[willie]

This is much easier to do with a computer model however.

Alan

Alan, Do you think that a FE type program, such as the  bow-simulator that was discussed a while back, would have potential for these type of observations?

[avcase]

This is much easier to do with a computer model however.

Alan

Alan, Do you think that a FE type program, such as the  bow-simulator that was discussed a while back, would have potential for these type of observations?

Yes, I do believe so. I haven’t spent much time in that program yet, but I believe it has great potental.

Alan