Thinking about sidearm catapults and preindustrial technology got me wondering about throwing rocks. A simple machine like a sling helps throw a rock farther. Flywheel catapults have been made but you have to stop them to reload. A bat also gets a rock farther but is more uncertain and probably harder to aim than a sling. An arrow goes the farthest but part of this is the aerodynamics of the arrow. Plus an archer or a slinger has a limited rate of fire.

The automatic bat defense is a bat mounted on a spinning wheel. The (heavy) wheel is spun fast using gears. Rocks are rapidly dropped one by one in front of the bat. The wheel and bat slows for each one but is back up to speed for the next and does not need to stop to reload.

A human batter can hit a ball 300-500 yards. I am not sure how a machine batter would do with rocks but probably comparable. The automatic bat could be put on a wall for defense or carried on a wagon. I think an automatic bat device like this would be better than a cannon against a cavalry charge, especially if the poor bastards being charged had all day to collect rocks (eg Waterloo).
-- bungston, Sep 27 2011

(?) Stone Slinger http://homerenovati...tramainimage_20.jpg
Uses fast moving coveyor belt to sling stones up to 90 yards. [rcarty, Sep 27 2011]

This is an excellent idea! You could have some sort of bicycle-driven device, with the horizontal bat-bearing wheel coupled to the pedals.

To get consistency of aim, I suggest a chute down which the rocks would fall, delivering them to a consistent point on the bat. Morealso, the chute could have a little gate, opened in synch with the rotation of the paddle wheel, so that the rocks would always meet the bat at the same height. The handlebars could be used to aim the device, and the gears could be used to vary the shot between a rapid hail of pebbles and a thud thud thud of larger rocks.

A few more ideas of this calibre, and the HB will be ready to invade Norway.

[+]
-- MaxwellBuchanan, Sep 27 2011


When life hands you lemons, use them as ammunition and point out that the unpredictability of their trajectories is actually even more disconcerting for the enemy than relentless accuracy.
-- MaxwellBuchanan, Sep 27 2011


Also, I'm not sure of the physics of batting irregular rocks. If the rock is struck by a flat surface, travelling orthogonally (ie, not putting spin on the rock), I'm not sure there'll be much (if any) effect of irregularities.

Obviously, the trajectory will be all over the place if the bat surface is curved, or if the impact has any lateral component, but that's a different issue.
-- MaxwellBuchanan, Sep 27 2011


I don't think it will matter much if the rocks themselves are spinning *a little* at the moment of impact. What I meant by "spin" was the bat striking the rock at an angle (as you would do with a cricket racket if you wanted to spin the ball), in which case the irregular shape of the rock would certainly be problematic. But if it's a square-on hit, I don't think there'll be much of a problem.
-- MaxwellBuchanan, Sep 27 2011


If the contact surface on the rock is not on a line perpendicular from the "bat" to the center of gravity, the irregularity of the rock definitely will matter. At the least it will tumble, and most likely go off at an irregular angle. A somewhat concave bat would probably help with this.

As [MB] stated, an irregular horizontal trajectory would be beneficial against a massed charge. An irregular vertical trajectory would be somewhat more problematic as it might miss the attacking line entirely.
-- MechE, Sep 27 2011


//If the contact surface on the rock is not on a line perpendicular from the "bat" to the center of gravity, the irregularity of the rock definitely will matter.//

I'm honestly not sure. I can see the rock spinning (if a protrusion to one side of it gets hit by the bat), but will it not travel forward?

I am somewhat pinot grigiod, and may not be thinking straight, but...

Imagine that the bat is held vertically, and is travelling from left to right towards the rock. Imagine also that the rock is initially stationary. (I know it isn't, if it's dropped into position, but its velocity can be very small compared to the velocity of the bat, so I'm going to pretend it's stationary.)

So, we have a bat with no up/down velocity component (Y) and no back/forth velocity component (Z), only left-right velocity component (X). The rock initially has no X, Y or Z velocity components.

After the impact with the rock, the bat's X velocity component will change a little but, because of the mechanism holding the bat, the bat cannot acquire any velocity in Y or Z - those are still zero.

Therefore, the rock cannot acquire any velocity components in Y or Z either. If it did, then the system overall would have acquired a net momentum in Y or Z, and you can't just go plucking momenta out of thin air.

Therefore, I contend, if the bat itself is moving orthogonally to its face, and if the rock is initially stationary, then the rock will be propelled orthogonally to the face of the bat, whatever the lumpiness of said rock.
-- MaxwellBuchanan, Sep 27 2011


Ah but you contend wrong. The missing momentum you are looking for is imparted through the bat handle to the machine and it's fixings.

If the surface of the bat and the surface of the rick were infinitely smooth or had absolutely zero grip, you might be able to contend that there could be no lateral impulse, but that's not the case at all.

When thinking about impact dynamics you need to think of everything as a combination of elastic (like a spring) and deformable (like playdough). A suitably hard rock and bat will be more elastic.

Okay so an extreme example. Get a long coil spring, say 300mm long and an 20mm round. Drop onto a concrete floor *exactly* perpendicular. It will bounce straight up,or at least you'd expect it to. Next drop it slightly tilted out of vertical. WIll it bounce straight up? No. As it compresses under impact it gains purchase on the floor and transfers impulse. As it recoils this impulse will result in lateral velocity. This is a suitable analogy for your rock with an irregular surface hitting the bat.
-- Custardguts, Sep 27 2011


//ideas of this calibre// ISWYDT
-- Voice, Sep 28 2011


The uneven rock will roll against the the bat, definitely imparting a tumble. This spin will cause it to curve in the air at the least.

I believe there will be additional effects as per [custardguts] but the tumble is a minimum.
-- MechE, Sep 28 2011


[custardguts], you are completely correct. Clearly, the fine threads of physics do not wash well in the harsh solvent of alcohol.
-- MaxwellBuchanan, Sep 28 2011



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