Author Topic: Bow design and development  (Read 41730 times)

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Offline Del the cat

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Re: Bow design and development
« Reply #60 on: November 04, 2018, 11:52:05 am »
    A compound isn't really a true bow.
  ;D Yup, I ain't arguing with that
Del
Health warning, these posts may contain traces of nut.

Offline DC

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Re: Bow design and development
« Reply #61 on: November 04, 2018, 12:21:09 pm »
It's just after breakfast here. But I guess beer is the breakfast of champions ;D ;D

Offline bradsmith2010

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Re: Bow design and development
« Reply #62 on: November 04, 2018, 12:39:32 pm »
DC,, could you explain to me in simple terms, ,what you think your experiment shows,, Im a bit confused,, )P(

Offline DC

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Re: Bow design and development
« Reply #63 on: November 04, 2018, 01:32:03 pm »
I'll try :) On page 164 of TBB4 baker talks a little about leverage. When I read this a few years ago it stuck in my mind the more leverage is faster. I'm going to read it again. Anyway with this more leverage thing in my brain one day I was thinking about why recurves didn't have as much stack. it occurred to me that as the bow was drawn the recurve would stick out effectively making the lever(limb) longer. If you don't know a lever is measured from the fulcrum(handle) to the point of effort(string nock). It doesn't matter what shape the limb is between those points, the lever is always measured in a straight line between those two point. I realised that with a straight bow as the limb bent the lever would get shorter and it does, by around an inch or so at full draw. I had to set up my experiment to check the recurved bow. I found that with the recurved bow the limb kind of stayed the same. While I was at it I tried an deflex/reflex bow and it gained length.
This length change is a gradual thing and depends on the amount of deflex/reflex/recurve so it varies.
With this in mind and the leverage=good in mind I put 2+2 together and came up with maybe 3.5. I'm not quite sure how it all fits together but I feel that the extra leverage at full draw can't be a bad thing. This must tie in with string angle somehow and one may just be the result of the other. Until someone can explain(in simple terms :D) the how and why string angle and leverage actually affect energy storage and delivery I'm just as ignorant as ever. I just thought I would show my results in case it jogged some physicists brain. There has to be someone out there that can explain this stuff.
Hope that helps, if not I'll try again :D

Offline bradsmith2010

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Re: Bow design and development
« Reply #64 on: November 04, 2018, 01:40:10 pm »
yes thank you I understand,,the reflex deflex is longer at full draw,,and could be part of its shooting advantage,, (R 

Offline Halfbow

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Re: Bow design and development
« Reply #65 on: November 04, 2018, 02:01:15 pm »
First let me say, I love this convo. This is the stuff I find fascinating.

There is a lot you can do with horn and sinew that you simply cannot do with wood. With regular hunting arrow weights the horn sinew bows are not all that much better than well made wood bows but with light flight arrows and short bows they can excel even though not many shooters today are getting the distances that are possible a few are getting some pretty impressive distances.
I agree. Except from what I've seen, short bows seem to do well with both heavy and light arrows. But indeed the drawbacks of horn and sinew (higher density and such) may start to catch up with it in lower draw weights. Though I theorize that something else is skewing the results here. Many people are making these comparatively light horn bows to look like the warbows and heavy flight bows of the past. With the higher density of sinew and horn, you have to be really careful what you do with them. The profile of a heavy horn bow can make for an unideal light horn bow ...that still preforms comparably with top tier wood bows.

The record shot by the sultan has been called in question and I myself am not convinced it was a real shot. But we do know it was very possible.

I've been frustrated by the lack of info I could find online about this. Most sources I found seem to accept it as historical fact, but details are scarce. I certainly haven't found anything very academic. If you could point me to that, or to the controversy about it, I'd be interested to read.



DC, fantastic test. When you started talking about lever length, I started trying to picture what kind of line the tips of various bows would draw in the air. I failed.  :P Then you posted that test! It's a clever way to test it, That could be really useful for trying to figure out ideal limb shapes for energy storage for various designs. I may have to try to recreate it some time, because I want to know about like 100 different variations. XD

The deflex won here, which is interesting. I'm curious how that holds up with different limb shapes and different amounts of recurve. But it made it occur to me that a bow with most of the working area near the handle, with a stiffer mid and outer limb, will have a profile more like a deflex bow. So extreme mollegabets and bows with smaller working areas and stiffer outer limbs, like Badger is talking about, are getting some of the geometrical advantage of a deflexed handle without necessarily actually having deflex.

I'm still trying to wrap my head around it fully, but I'm wondering if the more important measurement isn't something different than the lever length. I'm more tempted to measure the distance of the tip to the middle line. The line which the arrow will be along. It seems like that will have more to do with the leverage the string has on the limb. Like marked in red:



Or on recurves, measure from where the string lifts off. As before then, your bow is effectively shorter. Here is an extreme example to illustrate the point:



Here's a silly extreme example just to illustrate why I think this may be the more important measurement:



Imagine that's a tiny bow being drawn to 24". This bow would clearly be a nightmare to try to draw further. The string has no leverage anymore. Much stack. Yet the lever length is about as fine as it ever was. The distance from the middle line tells you more.

I have more to say about force draw curves, but I'm out of time so it will have to wait till later!
« Last Edit: November 04, 2018, 02:05:36 pm by Halfbow »

Offline DC

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Re: Bow design and development
« Reply #66 on: November 04, 2018, 02:18:12 pm »
I've done a test and marked where the string lifted off as the point of effort. It really makes a big difference. There are so many combo's of stuff that I just did the three easy ones. I wondered if anyone was going to mention using string lift off. I haven't done it with these limbs but I did it with a ridiculous amount of reflex the last time. At brace the string hit the limb about the middle. There was 4-5" of lever length change. It would have never been stable so I just put it aside.
I have to do some more but I have to make better limbs. These were just 1/8" panelling and took a lot of set.

Offline bradsmith2010

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Re: Bow design and development
« Reply #67 on: November 04, 2018, 04:43:54 pm »
nice (f)

Offline willie

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Re: Bow design and development
« Reply #68 on: November 04, 2018, 05:14:09 pm »
DC,
acceleration can be had at a steady rate, ie , where velocity can be increasing at an incremental amount that doesn't change. acceleration can also be had at an increasing or decreasing  rate. the rate of acceleration can be decreasing while the velocity of the arrow is increasing.

Code: [Select]
https://sites.google.com/site/technicalarchery/technical-discussions-1/arrow/accel%20vs%20time.png?attredirects=0
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https://sites.google.com/site/technicalarchery/technical-discussions-1/arrow/velocity%20vs%20time.png?attredirects=0
that being said, I will agree with Del that smoothness counts for a lot. I can't help but think that if a limb profile was developed that shot an arrow better than those used by most olympic recurve shooters, there would be much more variety in what is seen used in those matches. I am surprised by how similar most of those bows are.
If more speed or range is desired, it seems to me that staying within the design and upping the draw weight, draw length and arrow weight would be the place to look for an increase in performance
« Last Edit: November 04, 2018, 05:23:57 pm by willie »

Offline DC

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Re: Bow design and development
« Reply #69 on: November 04, 2018, 06:21:34 pm »
Hey Willie. I can't help but think that with something as high profile as the Olympics at stake that these factories must have a Skunk Works somewhere and like you say it's surprising how similar these bows are. Does the Olympics put any limits or restrictions on the bows? Maybe they are the best they can be or maybe the changes just aren't obvious.
I'm kind of stuck when it comes to draw weight. Just can't seem to pull much more than 40#. So When I started chasing speed I decided on 40# and 28" as my limits.

Offline willie

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Re: Bow design and development
« Reply #70 on: November 04, 2018, 06:57:46 pm »
I dunno about a skunkworks, but there are a few  top line manufactures  seem to dominate the market. Since accuracy is the primary driver of what flies and what doesn't, and these are repudiately the the best shooters in the world doing the "testing", the typical design would seem to be a good departure point for making improvements.
It would be an interesting to see if there are arbitrary restrictions that influence designs, but I am not the guy to ask, just a curious observer. I do notice that a lot of the interchangeable limbs offered seem to keep a decent width in the outer limb.

https://www.ocf.berkeley.edu/~archery/wp-content/uploads/docs/recurve-fundamentals.pdf

Offline DC

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Re: Bow design and development
« Reply #71 on: November 04, 2018, 07:25:08 pm »
I got this from the link you posted

Quote
For a cantilever spring, however, the DFC is non-linear, as both the
force and the differential force both increase as the deflection increases.

Can you explain this for me? I think this is something I have wanted to know ever since I started bending sticks

Offline loon

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Re: Bow design and development
« Reply #72 on: November 04, 2018, 11:37:01 pm »
As the cantilever spring is bent, both the force and the rate of increase of the force (the differential) increases. So, the force increases at a faster rate as it is bent, that just means that it stacks, while the coil spring doesn't stack, at least as quickly.
« Last Edit: November 04, 2018, 11:40:30 pm by loon »

Offline Badger

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Re: Bow design and development
« Reply #73 on: November 04, 2018, 11:48:07 pm »
  A bow limb gains very little weight because of bending it. The vast majority of the weight is gained because the string angles get higher and leverage is reduced.

Offline Bayou Ben

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Re: Bow design and development
« Reply #74 on: November 05, 2018, 08:56:06 am »
"My favorite method which I have never come close to perfecting and I think in the long run will prove out to be the most effective involves limb tapers matched to the curves in the bow which will allow for the limb to uncoil kind of the same way a fly line uncoils when cast. This is where the last part of the limb to uncoil is toward the tips. I still believe this design would allow for more working limb with less vibration and be more efficient. It would also allow bigger curves and more net reflex. "

Steve, so if I'm following you, on the case of a r/d bow, you would have more taper in the deflex area and less taper towards the reflexed tip area?