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The Slingshot Channel Thread

All non-spudgun related discussion goes here such as projects, theories, serious questions, etc. All "off-topic" posts (aka useless posting, determined by moderators) will be removed.
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Unread postAuthor: JoergS » Tue Dec 15, 2009 3:08 pm

Hello,

the time has come... the winners have been drawn. I have emailed each individual winner already, but here is the list:

Troy Boylan
Pitbull
Zolik
SaulG
John MacMillan
wiiplayer888
bdt
Blake Smith
jjh
Gustavo Tavares
Darby Dixon
Andrew
Yuri
hare basher
GearGuy92

All the winners have to do is to answer my email with the shipping address. I will take care of all the shipping cost, too, no matter where the winners live.

Soon, each winner will be the proud owner of a Baby Hook slingshot, designed and hand made by myself!

Thanks to all. 215 followers! That is quite a success.
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Unread postAuthor: McCoytheGreater » Thu Dec 17, 2009 2:00 am

How many times have you hit yourself in the thumb with those things? It looks like some of your creations could take it off at the knuckle! what are the differences in results with the black, blue, and red thera bands? Of course they shoot harder, but what about from an feet per second standpoint?
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Unread postAuthor: JoergS » Thu Dec 17, 2009 4:32 pm

The thinner the band, the faster the bullet. Thin bands have their biggest advantage with lighter bullets, the very heavy stuff does not show the same uplift. In general, the black bands are about 10% faster than the golden, and the blue gains another 5% or so. Beyond that, it seems the difference is marginal. But the thinner bands tear more easily. I have pretty much settled on black and blue bands for now.

And I never ever hit myself in the hand. If you shoot in a correct and clean way with all the angles right, then there is no danger.

You would see the hand scars and missing finger parts otherwise. A finger hit with a +500 grain bullet flying at +200 mp/h is serious, no kidding.
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Unread postAuthor: McCoytheGreater » Thu Dec 17, 2009 9:30 pm

I've been checking out the slingshot channel and blog a lot lately. Some pretty cool stuff on there. Makes me regret ever owning one of those dinky wal-mart slingshots. Should've saved money and just built my own.
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New "W"-Slingshot, 90% wood, made with common tool

Unread postAuthor: JoergS » Sat Dec 19, 2009 12:11 pm

The self centering "W" slingshot (original idea by Bill Herriman) is my preferred design right now. And many people love it, too, they want to have one... but as you know, I do not sell my slingshots.

So I have been thinking about a "How to" video. Problem is that for the stainless steel "W", you need welding gear and other rather expensive and unusual tools. People don't have these tools at home, so I had to come up with a wooden "W".

It turned out rather well, no metalworks at all. It is more bulky (10% lighter, though), but it shoots just as good. I am very pleased with the stability - no wonder, 1" wooden rods can take some strain.

The video is finished and currently uploading, but here are two photos for now:

Image

Image

Greetings from snowy Germany

Jörg
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Unread postAuthor: JoergS » Sat Dec 19, 2009 1:36 pm

Here is the video:

[youtube]http://www.youtube.com/watch?v=fQr8U34ugH8[/youtube]

Edited by jrrdw.
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Slingshots: How low can the fork be to still be safe?

Unread postAuthor: JoergS » Sun Dec 20, 2009 7:19 am

Several people have expressed concern about hitting your hand if the fork is too low.

I now use just 2.5 cm fork height above the hand in my "W" designs. This results to extremely low strain on the wrist, making the slingshot much more controllable.

I tested the setup with lots of super slowmotion stuff (1200 fps recording speed). The ball does not even come close to hit my hand.

But in order to confirm the field tests, I have started to calculate the setup.

It comes down to the research of Sir Isaac Newton.

He came up with so-called gravity laws.

The earth acceleration is 9,81 m/sec*sec.

Let us assume you have a draw length of 1,20 m (that is quite long). And let us further assume that the ball (15mm diameter, .60") flies with 65 m/sec at the end of the acceleration (V0 = 65 m/s, at the fork). That would mean that the average speed is 32,5 m/sec between pouch and fork.

In this case the ball would need 0,037 seconds (37 milliseconds) to reach your hand.

In this time frame, it would drop 0.5*981 cm * 0,037 * 0,037 = 0,67 cm (under 7mm).

The 15 mm ball passes the fork with its lower rim 1,05 cm over the top of the grip (= your hand).

The shot would have to fly as slow as 40 m/sec (at the end of the acceleration, so V0=40m/s) to make the ball just graze the tip of the grip. That would be a very weak shot.

This calculation does not even assume that the pouch moves towards the fork tips and counterbalances the gravity (a slight upwards vector is applied to the ball). So in reality, the drop is even less substantial.

But of course it would be easy to add another safety margin by making the fork ends higher. It would spoil the effectiveness of the design, though. And then of course the ball may still fall out of your pouch and then hit your foot. Ouch!

So I think it is fair to say that my design is well thought through, supported by the laws of physics and proven by field tests using professional equipment.

Bill Herriman pointed out to me that there is enhanced danger if you do wing shooting (= trying to hit a flying target). That is certainly true, as you may move the slingshot upwards during the shot. This would ruin the safety margin and I do not think that my "W" would be a safe design for wing shooting.

Greetings

Jörg
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Slingshots: How low can the fork be to still be safe?

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Unread postAuthor: CpTn_lAw » Sun Dec 20, 2009 8:34 am

I think the end of acceleration is not at the fork, but at the equilibrium ("sleep" length) of the bands. I think it would require a little more equation solving to find out wether or not , and the probability of each, the ball would hit you.

Edit : you would also have to make approximations for every parameter if you start making some for speed, , time, vertial acceleration etc... You would have to assume your hand is perfectily still, that the gravity is negligible in front of the force exerted by the bands for the time of the operation.
Now , in a real system, and not an ideal one, releasing the pouch makes it move a very little up or down, and on the sides; It also makes the wrist move, along with the hands and the forks. So IMO, physics (even if we don't do the proper system analysis) predicts that the ball will not hit you, but human parameters such as arm motion and wrist rotation up the probabilities of a hurting hit.
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Unread postAuthor: JoergS » Sun Dec 20, 2009 9:10 am

Well of course there is no ideal system. hence the safety margin of over one centimeter. Not needed in a perfect system.

My slow motion studies have underlined that even small movements of the hands do not cause major changes to the flight of the ball. Also, the ball leaves the pouch quite late, well after the passage of the fork.
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Unread postAuthor: john bunsenburner » Sun Dec 20, 2009 10:20 am

By all means, is it reallz THAT hard to make a hand protection on the sling?

The stuff you build is rather specific to a job, for example high velocity, low strain on wrist and so on, in the cases in which you have super low forks, you might as well build a little hand protector, so that even if you air at your hand you can't hit it.
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Unread postAuthor: CpTn_lAw » Sun Dec 20, 2009 10:59 am

The ball can leave the pouch late, but the bands are no longer pulling it once they pass the equilibrium state.
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Unread postAuthor: JoergS » Sun Dec 20, 2009 11:15 am

@ CpTn_lAw: Even though the tension maybe spent, there is still the accelerated mass of both the pouch and the rubber. But in general, I agree - that is why the "H" design works, with the built in draw length increase. That does not change my calculations, though - au contraire, it only means that the average speed of the ball on its journey from pouch to fork is higher than 0.5 * V0. Hence, even less of a drop.

@ john bunsenburner: Of course I could build a hand guard. I could also add a brake parachute to my car, in case the main brakes fail...

Seriously, I CAN'T hit my hand even if I aim at it. The hand is in an unreachable position for the ball.

Adding a hand protection would be useless and clumsy. Why should I add one? If you feel better with it, of course you can go that route.
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Unread postAuthor: john bunsenburner » Mon Dec 21, 2009 5:46 am

I am thinking of a 5mm fork set up, something mad and useless unless for a specific tast, and in that case a guard would be needed.

With normal forks no one should need to use a guard anyway, though I have hit my hand a few times, its really just bad holding positions, or overall uselessness of the shooter that cause that.
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Unread postAuthor: JoergS » Mon Dec 21, 2009 6:10 am

I even have tested a slingshot with no fork at all. Still works.

Here:

[youtube]http://www.youtube.com/watch?v=l4iVJkT-Ycg[/youtube]

Video embedded by jrrdw.
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Unread postAuthor: octocamo » Thu Dec 24, 2009 2:22 am

Man, i can't believe no one else has wowd at this.
WOW.
i'll make one of this things for sure!
one question: from what thing do you take that rubber? i use latex tubing for my slings, is that better?
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