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I completely agree with Aaron!

ZDP - you are a slingshot-scientist...
I like most of your cattys - and your comments seem to me well considered!

Regards
Torsten
 

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Thanks for the compliment!

I've started brain-dumping my thoughts about design and engineering of slingshots into the blog. I've little experience and they're just passing thoughts, so they don't really belong in the forum proper.

My main drive for now will be testing bands. I realised there's not much raw data published so I plan to do some more research in spare evenings to build a database of bandsets and elastics showing tables of brand, thickness, undrawn length, width, elongation, force, plus (once I get a chrony) pouch and shot mass and velocity. This can be used to understand the mechanics of the bandsets and build predictive models.

Eventually, I want to be able to enter a person's preferred draw length and acceptable draw force and churn out suggested bandsets and show a table of how the bandset will produce a predicted velocity with a range of shot masses. This can then be entered into roundball.exe and generate velocity, impact kinetic energy and drop for certain key ranges.

The old-school way is to make a set of bands based on experience and then suggest a range of shot weights that would work well with it. That's fine, but people's physiques, shooting styles and requirements differ a lot. If someone asks, "Hey, I'd like to shoot a target the size of a hare with 10 ft.lbs terminal energy at a range of about 20 yards from standing. I like a 3/4 butterfly stance or about 22lbs of draw at 53 inches. What do you recommend?", then it's hard to say, "Oh then you need to get a such-and-such bandset from this-or-that vendor and shoot with an x-sized steel ball." With the right data, it's just a matter of plugging the numbers into a spreadsheet.

Another use is when people are looking for an off the shelf bandset and don't know what to buy. They can look up the stats and know what's sufficient and whether they can draw them. They can also see what kind of shot gives a flat trajectory and sufficient energy for the task at hand.
 

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If you guys like ZDP's info you should read the info that I posted from the inventor of tapered bands almost 6 months ago.

http://slingshotforu...-tapered-bands/
You are a funny guy ZDP.I allways smile when you say I need a chrony as you say it manny times.(However I understand its expensive)

I replied on the wrong comment sorryTruckee
 

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I am actively looking for a F-1 or M-1, but they aren't sold here and it's a hassle buying from the States.
 

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ZDP, I think I might have the answer to the numbers your looking for. Ive been shooting .395 (92.5 grains) lead at around 250FPS and this will give you the 10 ft.lbs. at 20 yards that your looking for. Not to mention a very flat trajectory and plenty on penetration on impact. Ive been looking for the one sling/ammo that can do it all and I think this could be the answer. I don't think 250FPS will be a problem with you draw length of 53 inches. If you don't like lead you can use 7/16 steel.
 

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You are a funny guy ZDP.I allways smile when you say I need a chrony as you say it manny times.(However I understand its expensive)
I finally have an M-1 Chrony coming. It's 90 bucks for the machine and 70 for the postage. Businesses always seem to use shipping services that are appallingly over priced, whereas private sellers may actually weigh the thing and shop for a cheaper service.

I also have a new target coming. I'll combine the two and a bench rig and I can do some really detailed testing.
 

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It's official .....After reading the posted blog........I 've been stupidizied !

Great job Dan ! Such detail !

-Scott
My Wikipedia-fu is strong.

I love this forum. It's just because we're all so different in our styles and thinking that we make this an exciting and stimulating place. I imagine we were all stone-age hunters sitting around a camp fire.Jörg has just created the world's most powerful stone battle axe that only he can wield, I'm obsessing over the perfect shape of a skipping stone, Martin's laboriously crafting a Clovis point, Bill insists it'll never be as fast as a traditional pointed stick, Justin has just bartered a thousand arrowheads, danny has brought a skin full of trade items from the tribe over the mountain, etc. And yet because of our differences, we the tribe all go to sleep with full bellies and in good cheer.
 

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Dan, I did not know that you are a poet as well! Wonderful way to describe the forum.

Regarding the flatband / tapering issue, there is one thing I would like to point out.

Rubber is not weightless. The bands have to accelerate themselves, with the pouch and ball as "payload".

The rubber that is close to the pouch has to travel the longest distance and therefore its weight is the biggest burden. If you thin out the bands towards the pouch, then the weight of the rubber that is close to the pouch is reduced.

The draw resistance depends on how many rubber molecules are actually stretched. In other words, you can simply weigh a band set (made from the same rubber type) and then you can look up in a self made chart how much draw weight it will have.

However in order to maximize the speed of the band set, you want to do two things:

1. Reduce the inner friction
2. Taper the bands so the weight of the rubber close to the pouch is much reduced.

The inner friction can be reduced by using thin rubber. The rubber molecules in your bands are attached to their "neighbors". This attachment causes friction when the bands are stretched and released. The molecules at the surface of the bands do not have "neighbors" at the surface side, and this reduces the inner friction. So the larger the surface of your bands, the lower the friction. Ideally, a band would be just 1 molecule thick. However the tearing issue must be kept in mind. Thinner bands tear earlier than thicker ones.

The tapering works, that has been tested many times already. The more dramatic the tapering is, the faster your bands will shoot. However strongly tapered bands will tear earlier.

So we have to compromise! Use thin, but not too thin bands, and taper just the right amount.

Jörg
 

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The tapering works, that has been tested many times already. The more dramatic the tapering is, the faster your bands will shoot. However strongly tapered bands will tear earlier.

So we have to compromise! Use thin, but not too thin bands, and taper just the right amount.

Jörg
Attachment methods need development work. I think the best way lies with a flare or thickening and a rubber adhesive. It reminds me of the Trumark. It's a shame there's no research grants available! For now, understanding the bands we have followed by improving taper profiles and getting better band materials is my priority.

It's now taken immediate priority over frame designs, because I have lots of frames that work well and bands have a bigger impact on performance than the difference between two good frames.

It all kicks off when my Chrony arrives in 9 days' time and/ or when I get my TB Gold delivered from fish.

In the meantime, I will repeat the curves for the thinner XF1055 and XF1035 bands so I have an extra variable (thickness) for my model. I also just received Perry's bamboo shooter so I'm going to be busy with that for a few evenings.
 

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You are a funny guy ZDP.I allways smile when you say I need a chrony as you say it manny times.(However I understand its expensive)
I finally have an M-1 Chrony coming. It's 90 bucks for the machine and 70 for the postage. Businesses always seem to use shipping services that are appallingly over priced, whereas private sellers may actually weigh the thing and shop for a cheaper service.

I also have a new target coming. I'll combine the two and a bench rig and I can do some really detailed testing.
[/quote]

Great !I guess when you'll get it for a few days you won't be able to put it down just shoot everything thrugh it .
 

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Welcome to the Chrony club! -- Tex
 

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Kind of. You'd need weight, length and draw weight at a % elongation which therefore has a known 'k'. At least that applies to straight bands.
I disagree. The elongation factor is important of course. But the length does not matter. It takes the same draw force to pull out a 10cm band that is 1 cm wide to 40 cm as a 20 cm band that is 0,5 cm wide to 80 cm. Same amount of rubber, same amount of elongation. Of course the 20 cm band would shoot faster, but the draw force is the same.
 
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