Author Topic: Percent of energy storage to draw weight ratio  (Read 1139 times)

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Offline willie

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Re: Percent of energy storage to draw weight ratio
« Reply #30 on: February 13, 2018, 04:43:46 pm »
  The newer compounds are pretty efficient.......... I know they have very little limb movement.

the smaller movement would show a gain in efficiency due to a smaller hysteresis loss, but we often cite hysteresis losses as being around 10%.

even if a compound was 0 %, would that explain all the difference a compound has? efficiency wise?

Offline Springbuck

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Re: Percent of energy storage to draw weight ratio
« Reply #31 on: February 13, 2018, 04:52:10 pm »
With compounds, they have come a long way.  All the stuff that made them quieter makes them very efficient.  Parallel limbs, for one.

Offline gfugal

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Re: Percent of energy storage to draw weight ratio
« Reply #32 on: February 13, 2018, 09:39:43 pm »
Quote
SE/DW
if the compound max draw is 48#, is not that what you should  used in the SE/DW calculation? do folks in the compound world actually use this metric? 233% seems to be about the dropoff more than anything else
Well the ratio is based on final draw weight, which is usually the highest in traditional bows, but yes compounds are the exception. I suppose if you based it off that it wouldn't be quite so ridiculously high. If I use the max draw weight instead if final I get a SE/DW of 105% which is still good, but nothing fantastic. Compou d people (not that I am one, or know of any) probably don't use this value because they aren't into building compounds. I think only the engineers who make the bows for the company would care, and even then it's a less useful tool for them than it is for us.

Quote
is the compound more efficient?

is high early draw weight more efficient?
Compounds aren't inherently more efficient because of high early draw weight. The force curve and efficiency are two very different things. Just because you have one doean't necessarily mean you have the other. Sure they may frequently show up together, good energy storage and good efficiencg, in those cases you have a great shooter on your hands. Jowever, it's also possible to have one or the other as I gave example of before (although I would add that poor force curves will tend to lead to poor efficiency as well because if you have a bow that stacks bad it most likely is overbending to get those bad string angles. Therefore extreme set is likely which induces more hysterias).

So yes, modern compounds may be more efficient (remember my old one from the 80s wasn't efficient). But they may not necessarily be more efficient because of their good force curve and early draw weight. I'm guessing it has more to do with their materials and design that reduces weight, and minimilizes the distance the limbs have to bend.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Badger

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Re: Percent of energy storage to draw weight ratio
« Reply #33 on: Today at 08:19:48 am »
   I took an fdc on one this morning  77#@28". I plan to retiller down to 70# and flip the tips just a bit and am curious how much it will affect the FDC.  Starting at 7" and ending at 28" the fdc reads like this.    6-11-14-17-20-24-27-29-32-35-39-43-47-51-54-57-60.5-64-67-70-73.5-77. I figured it using the method of just adding up the numbers for inch pounds and then dividing by 12 for foot pounds. I cam up with 76.5 I believe. Curious what the actual number is. Going to retiller and flip tips now.

Offline willie

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Re: Percent of energy storage to draw weight ratio
« Reply #34 on: Today at 11:15:11 am »
interesting experiment , standing by for the news at 6

Offline Badger

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Re: Percent of energy storage to draw weight ratio
« Reply #35 on: Today at 11:20:55 am »
  I finished the heat treat and recurve process, it picked up a lot of weight. I had about 1 1/4" reflex at that time and now I have about 3 1/2, I hope to keep about 2 3/4. Try to get it tillered back down tomorrow.