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lonbow:
Very interesting videos! I think the biggest reason for the limb vibration is mass inertia. The limbs move forward and when reaching the brace hight, they are suddenly stopped. The mid limbs still have some kinetic energy due to their mass. I think a bow with no mass wouldn´t vibrate at all!
avcase:
--- Quote from: lonbow on April 08, 2019, 02:22:03 am ---Very interesting videos! I think the biggest reason for the limb vibration is mass inertia. The limbs move forward and when reaching the brace hight, they are suddenly stopped. The mid limbs still have some kinetic energy due to their mass. I think a bow with no mass wouldn´t vibrate at all!
--- End quote ---
The limbs reach their maximum speed around 2/3 the way through the shot and then the tips start decelerating even though the arrow is still accelerating all the way to the end. So it isn’t a sudden stop, but it is a rapid slowing. If the limb flexes between the handle and limb nock during this phase of the shot, then the center portion of the limb hangs on to a portion of that forward momentum rather than transfer it to the arrow.
One possible experiment is to clamp the handle and the limb tip down to something solid, then tap the mid-limb and listen to the frequency. A design that rings at a higher frequency between the nock and handle should be the better light arrow bow. A bow limb design with stiffer tips should have a higher natural frequency with with this vibration mode.
Alan
willie:
--- Quote from: Badger on April 03, 2019, 08:53:20 am --- 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.
--- End quote ---
Steve, i gotta ask if you built a follow up bow to that hinge bow, and where you took the idea?
DC:
--- Quote from: avcase on April 08, 2019, 03:03:53 pm --- If the limb flexes between the handle and limb nock during this phase of the shot,
--- End quote ---
This is confusing me a bit. What kind of flex are you talking about here. The bow is bending, that's flex, but I don't think that's what you're talking about.
Badger:
--- Quote from: willie on April 08, 2019, 04:30:51 pm ---
--- Quote from: Badger on April 03, 2019, 08:53:20 am --- 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.
--- End quote ---
Steve, i gotta ask if you built a follow up bow to that hinge bow, and where you took the idea?
--- End quote ---
I never did, I was trying to find some fiberglass builders to build the bow but none that I know of took interest. the new border bows closley resemble the design. The main thing I was trying to estalish was the amount of design problems that can be solved by simply using shorter working limb areas. Stability at brace for highly reflexed bows has always been a major issue, as well as the distorsion in the limbs that Allen described above. It solves both of those issue. Bows built from wood just cannot tolerate that short of a working area unless they are drawn much shorter. This particular bow could have tolerated a 24" draw pretty well without breaking down.
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