This tutorial will be showing you how to make both a simple TNT cannon and a full auto TNT cannon with dispensers.
Step 1: General Layout
These two pictures show the general layout of the TNT cannon with a bird's eye view onto it. If you are accustomed with Minecraft and understand all of this you can simply go ahead to creating it from here on, based on these pictures. For materials you will need the following:
-33 solid blocks, best are obsidian, end stone or bedrock if you are in creative mode.
-12 redstone dust
-8 TNT (for each individual explosion)
Make sure you have all these materials before beginning.
Step 2: Foundation
To start off you will build a 10x4 rectangle from some kind of solid blocks, best for this is obsidian as it will not break if the explosions sets of without the water stopping it from damage. Then you remove the strip of 8 blocks that you can see in the birds eye view. This is where later on the TNT is placed. Do not put in the TNT yet though. Continue by placing 2 more solid blocks onto the front two blocks off the left side. Next add a fence at the end off the gap and put a carpet/pressure plate on top off it. Add redstone in the places show . Next, add water to the very last block of the strip of air. If done correctly, you will end up with a water stream that goes right to the fence and stop there. Later on this will make sure the TNT does not blow up the blocks you use. If you want you can also add blocks underneath the water stream and fence.
Step 3: The Redstone Components
For this step simply follow the screenshot setup. You will need a total of 12 redstone dust, 10 repeaters and a button. Add the repeaters in the spots the picture shows, then place the redstone dust and add a button to the opposite side of the block with the water stream. Then set each of the repeaters to the highest setting possible (4 in game ticks)
Step 4: Setting Up the TNT
As seen in the above picture, the TNT will be placed along the water stream and one TNT on top of the carpet. Always remember!: DO NEVER PLACE TNT INTO THE WATER SOURCE BLOCK, this will just make your cannon explode as the water will later flow through the primed TNT, which it cannot do if you take away the source block. I also have a tutorial for the same concept just with an automatic aspect following this, If you liked my first tutorial then definitely look at it as well and maybe be inspired.
Step 5: TNT Cannon #2, Automatic Firing Cannon
This is the second, and more advanced TNT cannon which fires automatically for you, which means you only have to add as much TNT as you have into dispensers once and then just press a button. This is based on a redstone clock and dispensers, which is a kind of advanced subject in Minecraft, but I explain every single step clearly so you can follow even if you do not know what these are. FOr this second TNT cannon you will need all of the objects in the second picture:
-31 redstone dust
-66 solid blocks (Again any you want but obsidian, end stone and bedrock would be best because of their high blast resistance in case anything goes wrong)
-8 TNT for one explosion (As this is a full auto cannon you will want more to experience its full potential)
Step 6: General Layout
As before, we will start with a general 10x4 block foundation, in which you delete the 9 blocks as seen in the picture. Next, add water to the very last block inside of the indent and put a fence on the edge of the water. Put a carpet on top of the fence. This tutorial will also be color coded later on so I can easier explain the certain aspects in the next steps.
Step 7: First Dispensers and Extra Blocks
For the next step you will be adding some more solid blocks in the positions that you can see the orange wool in. This acts as a color code so I can more easily show you which blocks I mean, in which case for you these blocks would be the ones you chose as your solid blocks. Then, add the dispensers. Each of the has to be between the orange blocks and one block above them as well. Also you will move your whole row of these back by one from the original design so that the last TNT will touch the sourceblock of water. In this case this is not bad as the TNT is already primed when you put it in. Also this time dont place your repeater next to the launching tnt, which is going to be at the fenct. You can see this on the picture. After you do this, add blocks in the spot where the green wool is on the third picture. This is a 2x3 field which will hold aditional redstone later. Lastly add blocks in the position where the red wool is on the picture. This will be where the dispenser is later placed at and it also holds some redstone.
Step 8: The Redstone Aspect
This is the redstone aspect of the TNT cannon, not yet the clock. As seen in the first picture create a line of redstone accross the dispensers (Crouch so you do not access their inventory when right clicking the dispensers). And add a repeater so it faces the block behind the dispensers. Do not set any ticks on this repeater. Next you will add the redstone that leads to the launching TNT. For this place repeaters along the outside of the foundation, connected by a bit of redstone dust on the corner. These will all be set to full ticks. Now we come to the green part. As in the third picture. First connect the repeaters from the previous picture to the first repeater on the green field. Put another redstone dust behind it on the corner and connect this to the next repeater. Then we come to the red part of the build. For this, add a dispenser on top of the open block above the fence, as you can see in the picture and then connect up the redstone dust which then leads into a repeater that will power the dispenser. Both the repeaters on the green and red wool should not have the ticks set from the default 1 tick. Technically you are finished here, and you can use it as a semi-automatic cannon without a clock. For this just add a button the the end of the orange part and press it every single time you want to shoot. Be careful though, do not press the button before the last shot already went off, to not overload the system. If you want to make it fully automatic, follow on to the next step.
Step 9: The Clock
This is the last step in my tutorial on the TNT cannons. For this you will connect up 11 repeaters leading up to the little end tail part of the orange wool segment. These will all the set to full ticks. Then connect a line of redstone dust up from the redstone dust of the orange segment back around the repeater way and link the two lines up with another repeater as seen in picture 3. This repeater will control how fast your cannon is shooting: the higher the tick number, the lower the rate it shoots at. Last add a block with a button to the end of the repeater line. Then fill up the dispensers and press the button. Recheck your work and press the button to start launching TNT. To stop it launching just delete the connecting and speed controlling repeater until the redstone signal has totally shut down, then replace it. Thank you for taking your time on my tutorial I hope you enjoyed it and have a great time with your new TNT Cannon'(s)