Rock Thrower

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.