Tutorials/TNT cannons

A cannon is a mechanism that uses TNT to launch TNT or other Entities. The usefulness in SSP is limited because most cannons can only fire in one direction, making the cannon obsolete once the target is destroyed.

Basic Concepts
A cannon is made using two sets of TNT: The Charge and the Shot.


 * The Charge is a large amount of TNT used to propel the Shot.
 * The Charge is housed in a fluid to stop it from destroying the cannon.
 * The Charge is activated first, and the Shot is activated before the Charge explodes. It is important not to activate the Shot at the same time as the Charge, or the cannon will explode.
 * Redstone is used to activate each block of TNT in the Charge simultaneously.
 * The Shot is often held slightly above the Charge to alter it's tragectory.

Building materials
Most people choose to make cannons out of stone or cobblestone due to its availability, but you can make it out of any solid (preferably gravity resistant) block, such as Dirt, Wood or even Diamond. You can use TNT resistant Obsidian to make a 'dry cannon' which doesn't require water to remain intact between shots, but it is extremely difficult to correct problems if you place a block wrong in the construction phase.

Cannon Sizes and Common Features
When players discuss cannon size, they usually refer to the Charge size. Larger cannons have a larger charge which usually makes them fire further.

Players also like to add features to their cannons including:
 * Multiple shots
 * Semi-automatic firing and reloading
 * Charge Booster (Another piece of TNT that explodes, pushing the Charge towards the front of the cannon to concentrate the blast.)
 * Safety features
 * Adjustable Shot Delay, which changes when the Shot is activated.
 * Alternative Ammo

One-Button Middle Range Cannon
The following is a simple cannon that covers automatic delay. Please see this video tutorial if you need additional help.

Materials
- Base Material: (all solid blocks can be used)

- 1x Water Bucket

- 6x Redstone Dust

- 2x Redstone Torch

- 4x Redstone Repeater

- 1x Stone Button

Shot Mounting Blocks
The shot mounting block alters the height of the Shot once primed. Even slight changes will greatly alter the trajectory, and players use a mounting block to fine tune the cannon. Generally, the higher the Shot is elevated by the mounting block, the higher the angle of fire but the lower the velocity.

Pros: Highest velocity, simple, scalable
 * No Mounting Block

Cons: poor range in smaller cannons, downward trajectory, line-of-sight only

When no mounting block is used, the Shot is either allow to fall onto the water trough or is place on the trough directly. the Shot will fire out completely horizontal, or 0°. Gravity will quickly pulled the Shot to the ground, giving a very flat, downwards trajectory.

With small TNT charges, the range can be extremely limited. To increase the range, ever larger charges are needed or the cannon must be built higher above the ground. A larger charge means a higher velocity to the Shot, pushing the Shot farther away before it drops to the the ground.

Players have been known to use up to 70 TNT charges and beyond. But economically, a cannon without a mounting block will take more TNT and longer to load for a certain range.


 * Single Block

Pros: Higher firing angle, can "lobe" shots

Cons: Low velocity, reduced power and extremely poor range for smaller cannons

A single full size block such as cobblestone or obsidian is placed under the Shot. This has the effect of elevating the Shot above the water trough, so the blast force from the Charge is applied not just forward, but upwards. The shot is fired out at a high angle and trajectory. This is useful for hitting a elevated target, or one behind terrain or obstruction.

However, part of the blast force is absorbed by a solid mounting block, so the cannon will suffer similar problems of needing large charge sizes. Also, since some of the energy is expelled in the upwards direction, forward shot velocity is reduced greatly.

A better alternative to the single mounting block is using a Ladder instead.


 * Half Block

Pros: Smooth trajectory (not too high, not too low), average velocity, more efficient for small and medium cannons 

Cons: Slightly reduced power, not best for either straight OR lobe shots, fuse range limit * 

A half block is the compromise between a single block and no mounting, and generally more efficient than either. More of a cannon's blast force is directed forward, but there is still an upward vector that raises the angle of fire to roughly 30°. As with a single block, some of the blast energy is absorbed by the block, but much less. From the same TNT load, the half block has greater range than a single block or no block.

When the TNT Shot is initially placed over a half block, it will hang over the half block as if it was a full size block. Once the TNT has been "primed", it will fall down and sit on the true height of the half block.

The firing angle produced by a half block is good for extending the range of a cannon and hitting elevated targets, but its too low for effective lobing over high walls and obstacles. For straight direct firing, shots fired with a half block mounting generally land level on the ground within a certain range. However, due to the limited fuse time of TNT in the game, scaling up the TNT charges up to a point will result in the shot flying too high and exploding in the air before it lands or reach the cannon's maximum range. This will be refer to as the "fuse range limit * ". All cannons are limited by the fuse range limit, but cannons firing at higher angles are especially prone to the fuse limit, as the shot velocity is lower and shots reach higher altitudes.


 * Trap Door

Pros: (closed) Optimized for flat trajectory, velocity almost the same as no-block, (opened) can be used in open position for higher firing angle, good scaling

Cons: Be sure that priming circuit doesn't activate the trapdoor by accident.

If the firing angle of the half block is too high for your purpose, a closed Trapdoor can be used instead. Like the half block, it provides some upward force to the shot by elevating it above the trough. A trapdoor, however, is only half the height of a half block. Firing angle is roughly 15-20°, making it extremely effective for straight shots at very long range (+180 block).

Little forward velocity is lost when firing, and shot typically fly out at very high speeds. This combine with the low firing angle means cannons firing larger loads can extend their range without encountering too much fuse range problems as with the half block or ladder mounting.

As Trapdoors flip upwards when opened, they can be used to support the Shot the same way as a Ladder mount. Trapdoors can hence be used in both both a low angle and high angle firing mode.

NOTE: Be sure that your priming circuit for the Shot doesn't activate the trapdoor, or open/closed the Trapdoor beforehand.


 * Ladder

Pros: Efficent with small and medium cannons, High firing angle, parabolic trajectory, good for lobing shots and high alititude

Cons: Low velocity, poor scaling, limited range at ±120 blocks

A Ladder placed on the side can serve as a very effective mounting block for firing at high angles and lobing shots. A primed Shot will be supported by the edge thickness of the ladder, preventing it from falling into the trough. Because a Ladder is not a full size block, none of the energy from the blast is absorbed, and the shot is propelled out at full force. By adding ladders above each other, different firing angles can be achieved. Typically, a single ladder will give an angle just higher than a half block, roughly 40°-45°. Two ladders will give an extremely parabolic flight, shots fly out at about 50°-60°.

A good portion of the blast energy directed upwards on the block, so shot velocities are generally much slower than a no-mount or half block mount cannon. In return, a cannon have no problem lobing shots over terrain and walls. At larger charge loads, shots can reach very high alititudes.

However, this also means the fuse range limit is a inherent problem with this mounting. Within a 100 block distance, well built cannons level with the ground can expect to land shots low enough to cause damage. But beyond this shots explode midair way beforehand, even with a shot primed at maximum fuse time with a delay circuit. Hence, one can't simply add more TNT to increase the range, as it will only make the shot fly higher. A basic solution is to put the cannon below ground, in a dugged pit with a slanted slope to allow the shot to fly out. Since the shot had a lower starting point, it will explode closer to the ground once its fuse time runs out. To reach ranges beyond 150 blocks, this solution becomes impractical.

Video examples

 * | Mortar High Angle Shot using a ladder mounting block.
 * | Compact The Shot is primed by hand, which must now be done with flint and steel.
 * | Superlarge Cannon Firing other Entities.

Trivia

 * Cannons can launch any entity, including mobs, sand, gravel, or players. Sand and gravel can be used to mark the landing spot (assuming it doesn't despawn mid-flight).


 * Cannons are ineffective against water based defenses since TNT doesn't destroy any blocks when submerged.


 * Cannons are follow the South-West quirk and fire further when facing South or West.