this is just for demonstration and shows my fully functional automatic tnt cannon(s) made with redstone:

it took me many builds and tries and a few weeks of time but i finally succeeded in creating a fully functional automatic tnt cannon with either quad bullet or single bullet capability's.


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DETAILS:
while most automatic cannons fire automatic and reload automatically they still need to be difficultly manually reloaded in the end, this cannons automatic function however is a bit diffent, it means it autonomously reloads and fires itself as long as the device is offered enough tnt, it simply places the tnt in the appropriate way inside the cannon, detects when it is full and fires the full cannon, it then starts to reload itself, this process of firing and reloading is looped which makes this cannon a fully automatic cannon.


on the load platform the loading piston is hooked up with a BUD(block update detection) switch for ''full and fire/empty and feed me'' functionallity which is hooked up to a signal stabilizer due the bud's unstable output, which when it becomes stable for 1 a 2 seconds signals it is full sending a signal to a timer which stops the system, fires the cannon, then restarts the system again for a next session.
can be either switched of by a lever or a memory cell at the bottom of the system (the memory cell is just before the clock and can be identified by a piston and a button near it (this cell also bypasses the on off torch/switch)). the system lights and funcionallity can also be shutdown by removing its power supply (the highest redstone torch of the device near the on of off switch)

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UPGRADE TO MK2 (adding a manual fire mode, perhaps i will do this for you sometime soon if im bored again)


a possible MK2 version would come with a function to switch to manually fire and back, for a player may want to load up the cannon but not fire it when it becomes full. this effect can be achieved by placing a memory cell and AND gate just before the trigger wires, when the cannon is full the memory cell gets activated by the timing circuit and while normally the signal goes though activating the cannon this time it is stopped by an AND gate, the second input for the AND gate comes from a button (with indication light it is ready to fire hooked up to the memory cell) which should be located near a player reachable area, perhaps the loading area itself, after the button is pressed the memory cell becomes reset (shutting off the fire ready light) but before it resets the AND gates receives its needed signals which would allow the cannon to proceed with its firing sequence firing the cannon and starting up the process of reloading once again. to switch back to regular mode, a lever hooked up to a piston push/pulling a block bypassing the AND gate/memory cell combination should be able to do that rendering the fire button useless.


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INSTALLATION:
download the schematic and use mcedit to place the shooting range into a world or download the world file and unzip the .zip file, place the new 'automated cannon' folder inside your saves map @ %appdata%roaming/.minecraft/saves then log in, enter the world and you just need to keep feeding the cannons tnt like hungry caterpillars eat leaves... endlessly.


the cannons initially are loaded so they only require 1 tnt to fire, after the first shot the device requieres its normal tnt amount to function (either 18 or 38 tnt blocks depending on cannon)



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CONTENTS:
1x 4shot 30charge 4 condenser tnt cannon which can fire about 500 blocks with a proper length barrel.
1x 1shot 15charge 2condenser tnt cannon which shoots 200 blocks, and doesnt need a barrel to be accurate.

it also features the 4 shot barrel in a setup i made for my huge battlecruiser project: www.planetminecraft.com/project/very-large-spaceship-battlecarrier-class/ by request



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UPDATE 09/04/2013:

went from version 1.4.7 to 1.5.1.

the contraption has been tested and does not fail to work in the current 1.5.1 update.

even though BUD switches should have been eliminated, this contraption has a BUD switch that continues to work which results in a working contraption.

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view my crappy video for details if you want but i highly recommend you take a look yourself.

PLEASE give proper credit to me when using this or parts of this cannon in any public way.

Additional Notes

ps, if anyone would like to make a better video, please do so, if you have any questions ask them as far as/when the video cant awnser them.

pps, this cannon is not dependent on any orientation, orientation will however affect effective firing range like all cannons. with north west being furthest reaching and south and east being the lowest. (if im correct).