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Rock Thrower

Like an atlatl, only for rocks
  [vote for,

Logically, this device should have existed somewhen in History, but I've never heard of it. Sure, I know that a "sling" is a type of rock-thrower. However, a sling does not resemble an atlatl (see link) in the slightest. So, why isn't there a rock-thrower that resembles an atlatl?

I have a suspicion as to the Answer of that Question, and it relates to the two notions of "hold" and "release". When you put the back end of a spear into an atlatl, and use your arm to accelerate the device, there is a "lever arm" effect that enables the spear to become separated from the atlatl in a good way (good for making the spear travel a longer distance than if the atlatl was not used).

A rock, however, cannot exhibit any such lever-arm effect. When it is placed into the holding-part of our atlatl- equivalent, such that we can accelerate it, there is nothing in the overall natural motion to cause the rock to escape that holding-part. So the rock stays held right through the point where we might want to release it, for a long- distance throw.

Meanwhile, the different design of a sling easily accommodates both "hold" and "release", because the user simply lets go of one of the cords at the proper moment. This lets the rock escape the holder-part and begin moving tangentially away from what had been the acceleration- circle. (By the way, old carvings of armies that fielded both archers and slingers had the slingers Behind the archers, because they could out-range the archers.)

So, to have an atlatl that works for rocks, we need to add something New, a way to make it release the rock at the proper point. What I shall propose, just to have a completed Idea, involves a kind of "door"... (although plenty of other methods will probably work as well).

Imagine the holder-part of our Rock Thrower to be shaped somewhat like a box. It has a bottom and four sides, but no top (because we put the rock into the box through that opening). When the Rock Thrower is accelerated, the centrifugal effect causes the rock to impart force against one of the sides of its box. THAT is the side we convert into a door.

Not exactly a door, however; think "see-saw", which has a pivot-point and two sections that move in relation to the pivot. We want one side of the see-saw to be our door, and we want the other side to be a kind of control-point. Now we add, alongside the main shaft of our atlatl- equivalent, a simple lightweight hollow rod that presses against the above control-point. The hand holding the Rock Thrower uses its thumb to press against the rod, which pushes against the control-point, which keeps the "door" closed on the box holding the rock.

At the right moment during the acceleration of the Rock Thrower, the thumb is moved. The centrifugal effect, acting on the rock, easily causes it to overcome the lightweight rod's own centrifugal effect upon the control point (especially because we can ensure the rod touches the control point very near the pivot; the "force times distance" of the rock will greatly exceed the force-times- distance of the rod). Thus the door is pushed open and the rock escapes, free to now travel a nice long distance.

As a perhaps-slightly-better alternative, the thumb might be inside a Ring at the end of that hollow rod, and we physically attach the rod to the control-point (probably with a hinge). Moving the thumb could mean pulling on the rod and pulling on the control point, thus directly opening the door, so that none of the rock's available Force need be expended to escape. It could travel farther, that is.

Vernon, Oct 16 2013

Atlatl https://en.wikipedi.../wiki/Spear-thrower
As mentioned in the main text. [Vernon, Oct 16 2013]

Jai Alai http://en.wikipedia...e:Chist%C3%A9ra.jpg
[Klaatu, Oct 16 2013]

Staff sling http://en.wikipedia...weapon)#Staff_sling
Like an atlatl, only for rocks. [spidermother, Oct 16 2013]


       Scroll, scroll...must be [Vernon]...yeah, hi, how you doing?
normzone, Oct 16 2013

FlyingToaster, Oct 16 2013

       What FlyingToaster said - only with rocks.
Zeuxis, Oct 16 2013

       //slingers behind the archers, because they could out-range the archers..   

       Pardon? Or is that just the pre-Agincourt carvings?
not_morrison_rm, Oct 16 2013

       [Flying Toaster] (and others who added some links), to the best of my knowledge, in order to properly use those devices, you have to suddenly stop moving the device in order for the accelerated object to escape. But that is not how you use an atlatl. And that is not how you use the Invention here.   

       [not_morrison_rm], yes, pre-Agincourt (mostly ancient Egyptian)
Vernon, Oct 16 2013

       Don't bring a rocklotl to a gun fight.
4whom, Oct 16 2013

       // you have to suddenly stop moving the device in order for the accelerated object to escape //   

       True for the tennis ball thrower. I think for a staff sling you mearly have to stop accelerating it. The sling portion will then catch up, and trigger the release.   

       It does seem like a device with a precise release control could be more accurate with less practice, than a staff sling, but that advantage might be outweighed by the fact that your thrower is less energy efficient. With a staff sling, the total radius of the rock's path is covered partly by the staff and partly by the sling, so the rigid portion of your thrower will need to be longer (and heavier) than an equivalent staff sling. The box on the end will also add mass. To get the same velociy for the same rock, you have to accelerate more mass to the same angular velocity. After release, that extra mass at the end of your stick is also a disadvantage if you want to avoid slamming it into the ground.
scad mientist, Oct 16 2013

       [lurch], let us see if an ASCII sketch can be useful here:

       Due to the limitations of ASCII sketches here at the HalfBakery, I'm drawing this with the handle on the right and the "box" at left, only upside- down. The double-lines represent the main body of the device; the single long horizontal line at top is the lightweight rod, ending where a thumb could affect it. (I would have made them longer but ran into the 30-character limit.)   

       The short horizontal line at the bottom-left of the sketch is the Bottom Edge Of A Side-Wall of the box, so the box is actually Open in the downward direction; you put the rock through that opening into the box.   

       At the left side of the sketch (three vertical lines are actually One line) is the see-saw Door. When the whole thing is held so it is vertical, the Door is at the top of the device.   

       Normally, of course, the device starts out horizontal with the box opening upward. Insert rock, grab handle, push rod against the control surface of the see-saw Door, and start accelerating the device toward the vertical orientation. At the appropriate moment (near the vertical orientation moment) move thumb so that the Door can open and let the rock fly.   

       [spidermother], I did say in the main text that there are probably a lot of ways to do what I've described. I think I did know about "staff slings", but discounted it as being more of a variant of the sling rather than of the atlatl. Your opinion may vary, of course.
Vernon, Oct 16 2013

       Just going by the description and the pictures, the sling seems to be short compared to the staff, acting mainly to hold and release the stone (unlike a hand sling or a trebuchet, where the sling is much longer). I suppose it's a matter of degrees.
spidermother, Oct 17 2013

       Sounds to me like all you really need is a modified golf club, suitable for hitting rocks while they sit on the ground. The main modification would be some padding on the head of the club, to keep from shattering the rock at impact.
Vernon, Oct 18 2013


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