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[Hetairos]

After half of my fort and most of the soldiers died to an overdose of ‼FUN‼, I started looking into ways to create automatic defences. After learning about the impulse ramps, I decided to utilise them to develop simple, fully or semi-automatic minecart based devices intended to fling dangerous objects into things too alive for my taste. After countless alterations to the original design, usually not working as supposed to, I finally made the damn things work. They are intended to be as small and simple as possible while retaining their killing power. There is even smoke (actually mist, but hey)!

I apologise for the poor quality of the screenshots - my GIMP-fu isn't the greatest. I hope they're at least legible. They are intended to show an example battery of watercannons facing east, so any given directions must be altered if one wants them to shoot elsewhere. Color-Coded for Your Convenience!


Section 1: Fire

The "barrel" of the cannon. Makes the cart hit a fortification at high speed and drops it into the next section, where it is reloaded. It can be made longer, sacrificing rate of fire and (a tiny amount of) missile velocity for the ability to fire for longer periods of time before having to wait for the Reload section to refill, since it stores more water at a time.



• W->E Rollers (highest speed) - built upon normal E track. The minecart starts here - create a temporary route with a stop on the rollers (remember to switch off the power supply, or premature ‼fun‼ may ensue), assign a free minecart and forbid it once it's in the right place. Note the wall behind - it stops the returning minecart where we want it to stop.

• Gear Assembly (power source) - provides power to the rollers. Linking it to a lever allows one to switch individual cannons in the battery on and off as needed. Only one of them can border the rollers of one cannon for reasons I will explain while describing the next section.

• Floor Hatch - the minecart returns to the starting point through here. Opened by a Pressure Plate in the next section. Put a floor or something that will function as it, such as a wall or a bridge - otherwise the minecart may fly out into the air and land somewhere behind the cannon, possibly on somebody.

• Pressure Plate - linked to the Grate, the minecart triggers it on its way there.

• SE Track Ramps - impulse ramps. 4 are enough to make the minecart launch its cargo upon hitting the fortification without lodging the cart in there. Of course, nothing will happen on the first run due to empty minecarts, but it quickly ceases to matter. The wall to the south is necessary for them to work, but a neighbouring cannon can use the same wall if the "side" direction of the ramps is inverted (here SE → NE).

• Bridge - under this 2-tile bridge there are impulse ramps pushing the cart back to the start. They can't have a constructed track floor over them without becoming unusable and unable to impart speed, and a bridge acts just like track when friction is considered, while not acting as a construction in the DF sense. Not linked to anything, but if retracted may be used to access the lower levels of the cannon.

• Floor Grate - when it retracts, triggered by the Pressure Plate, the minecart falls onto the first impulse ramp in the loading section. A grate has the same delay as a bridge, but doesn't throw the minecart in random directions. A fortification stops the cart on this tile, while allowing it to send a deadly water glob in the general direction of the enemy.


Section 2: Reload

Here the minecart is again filled with water, as long as the depth remains high enough. See section 1 for notes on expansion. The whole section is obviously meant to be flooded with water. It would've made the screenshot a bit less legible, though. The system of walls and bridges separating it from the water source is unnecessary - replacing it with a chain of 10x1 bridges is the more optimal solution. An updated design is depicted in post #6.



• NW Track Ramps - also impulse ramps. Rollers can be used as well, but have to cover the entire distance between the pressure plate and the starting point, and don't automatically return the minecart to the start when the power supply is switched off, unless a separate power supply is provided. The rules regarding walls still apply.

• Pressure Plate - linked to three things: the Floor Hatch next to it, the Hatch in the first section and the Gear Assembly in the same place. This has the effect of opening the way to the starting Rollers and keeping them from pushing the cart back into the hole it emerged from. The hatches grind shut right before the cart resumes travel. Note that having two pressure plates send signals to one gearbox powering two sets of rollers, which seems like a nice simplification at the first glance, in fact won't disengage it, and the carts will get pushed back into an endless loop in the Return section.

• Floor Hatch - covers the passage to the next section. Without it, water wouldn't remain in the Reload section.


Section 3: Return

Sends the minecart back to the start, allowing the cannon to fire again. Can't really be expanded, not that there's any reason to do it.



• SW/NW track ramps - exactly 3 impulse ramps are required to send the minecart up 2 ramps to the start. 2 are not enough, whereas 4 and more make it spill its contents upon return and impacting the wall. The space above them must be channelled open or they won't work - this is visible on the screenshot depicting the second section.

• Floor grate - when the Hatch in the previous section is open, some water will inevitably flow through. A drainage system is required to, well, drain it to prevent it from staying in this section and breaking the system.

• EW track ramp - the cart leaves through here, and goes up another such ramp before returning to the Rollers, where it waits for the gearbox to switch back on.


Known issues

• The accuracy is abysmal. Don't expect it to snipe things from afar; this is compensated by limitless, high-power ammunition.
• The rate of fire in missiles per tick is impossible to exactly determine - carts behave oddly on submerged impulse ramps, probably due to the flow, and after retracting the grate usually hover in the air for a few ticks, give or take 1 or 2.
• The whole thing may freeze in winter, if put outside. I built it in a warm biome, so I can't tell how to protect against it. As long as there is water and a power source, the cannons can be fully contained inside the fort, even deep in the caverns or wherever you want them to be.
• Trees can and will stop missiles.
• Creatures may wander onto the tracks. The results are never pretty.

Other notes

• There is no real reason I am aware of for the device not to work with magma. The "push" from impulse ramps may not be enough to move the cart through thick molten rock, so using rollers instead might be a wise decision. Beware of magma mist!
• Remove the rollers, and with them the need for power, and you'll get the semi-automatic version. It requires a dwarf to push the minecart and a permanent single-stop route, so there is a limit to how many can exist at a time, since the list of routes doesn't scroll.
• Except for the mechanisms and a rope/chain for the rollers, all elements can be built out of wood, so it's a somewhat feasible defence for an early fort, not requiring deep digging and - provided you bring some stone and a rope - even piercing the aquifer.
• An aquifer could probably be useful, e. g. for drainage.
• No schematics are provided for the drainage system and the water supply, since their shape depends on fortress layout, terrain, presence of an aquifer etc.
• After some changes, I think a cannon could be used as a starting point of a system delivering magma to the surface.
• Running out of "ammunition" might be prevented by using pumps to keep the "load" section supplied with water. However, it would require significantly more complex infrastructure and a sufficiently large water source. It's possible to prevent the enemy from destroying the pumping system by encasing it in obsidian, which again increases the project's complexity, but might be worth the effort and is certainly very dwarfy. I humbly ask anyone who manages to pull it off for screenshots and a description of the system.


I sincerely hope the whole thing isn't redundant, but all designs I had seen before were significantly more complex, as well as taking up way more space. Feel free to ask questions or provide suggestions - I will update the post if something isn't clear enough or a way to improve the design is discovered.

Thanks to QuantumMenace for inspiration, and to fricy and all other contributors for the useful tool that the Minecart Speed Calculator is.

[wierd]

ITG recently discovered something that may be of interest to you.

It appears that closed bridges that are set for deconstruction, then subsequently have that order cleared on them before unpausing become semi-permiable, while remaining unpathable, and immune to building destroyers.

They are capable of allowing hurled objects, and flowing liquids to pass through them.
This may allow your waterguns to be completely inside a warm fortress, and thus prevent them from freezing over, as well as keeping inactive cannon ports from being possible routes of admission for certain stealthy creatures.

I haven't looked too carefully at your design (this is not a critique!), but it might be something to look into as a possible source of improvement.

[Hetairos]

Oh yeah, the bridge thing. Sounds a bit exploity, but so do impulse ramps. The cannons can already be put inside the fort, as long as there is power and water - even used to protect the caverns. The upper level is isolated from the outside with fortifications, and the lower one with raising bridges (or floodgates, but bridges are cheaper and immune to building destroyers), so nothing should be able to get inside. I suppose enemies might shoot through the fortifications, but that would put them into the range of the cannons, and nothing should be allowed to walk around the firing section while they're active anyway.

As for the lower level, I suppose this trick could be used to resupply water when swimming building destroyers are waiting outside. Kind of tedious for a large battery... unless I don't actually need that many bridges. I'll test this and whether such a bridge could replace the grate in the Fire section.

[blue sam3]

For the running-out-of-water thing, couldn't you just have a load of pumps set to pump into the reload constantly from a river or something, so you never run out of water, without needing to make it longer?

[Hetairos]

For the running-out-of-water thing, couldn't you just have a load of pumps set to pump into the reload constantly from a river or something, so you never run out of water, without needing to make it longer?

Hmm... that could work, as long as you don't exhaust the source of water, don't accidentally spill it over half of the map and have enough power. One pump needs 10 power, and you'd need more than one, unless the cannon battery in question is very small. For a larger one, probably nothing short of an aquifer or a major river would suffice. And the whole thing would need to be immune to building destroyers, so you'd probably end up using up more space and resources than you were trying to save. It would also need a specially designed entrance, since the "fire" section would have to be positioned two z-levels above the water source, and thus not on a river bank or something. And as far as I know, it would brutally murder the framerate.

But perhaps all that could be a price worth paying, for a few screw pumps can displace liquids in impressively short amounts of time.


I missed one quite important thing - there must be a floor above the "return" hatch or the minecart will fly out of the hole instead of properly rolling back to the start. Also, impulse ramps don't need any walls but the ones to their sides to function - those between the moat and the "loading" section are leftovers after using normal W track ramps. OP updated with necessary information.

[blue emu]

For the running-out-of-water thing, couldn't you just have a load of pumps set to pump into the reload constantly from a river or something, so you never run out of water, without needing to make it longer?

And the whole thing would need to be immune to building destroyers...

Obsidianize it. Mechanical devices like gears, axles, pumps etc continue to operate normally when entirely encased in obsidian.

[Hetairos]

Here is a better way to set up the bridges around the "load" section. Note that the bridges themselves aren't necessary for the cannons to function, but might be useful if you spot a swimming building destroyer heading in their direction or need to fix or change something inside. The amount of space between the ramps and the bridges can be of any size.



A Stonesense view:

[McDonald]

Incredible. I've never used minecarts before because I thought that they are too complicated for me :S. This is fully automatic, right?

[Hetairos]

Incredible. I've never used minecarts before because I thought that they are too complicated for me :S. This is fully automatic, right?

Yes. If you look closely on the "fire" section, you can notice that each cannon receives power from a different gear assembly. All those gearboxes are linked to the main axle to the left, which is connected to the power supply of your choice. Switching the cannons on is a matter of toggling a single gearbox between the power supply and the main axle. Link the gear assemblies next to the rollers to other levers if you want to control individual cannons. Skip the rollers and gears to create a semi-automatic version, where a dwarf has to push the minecart every time you want to fire a shot. Nevertheless, it has the benefit of not requiring power.

It took me about two in-game decades to come up with that design and to iron out all the issues I encountered, mostly due to a dwarfpower shortage, but it's actually quite simple. A minecart fires a projectile, is dropped down to refill and then returned to the starting point to begin the cycle anew. Each cannon presented here is 13-14 tiles long and needs 3 z-levels, not counting the drainage or the water supply.

[Ravendarksky]

how do you stop the minecarts going through the fortifications?

[Hetairos]

how do you stop the minecarts going through the fortifications?

That shouldn't be happening, unless you go overboard with minecart speed or replace the floor grates in the first section with floor hatches. Hatches open immediately after a signal is sent to them via lever/plate, creating a tile of empty space right before the fortification. In such conditions carts fly through fortifications for some reason.

Minecarts sometimes end up in the fortifications, if more than 4 impulse ramps are used for acceleration.

[Ravendarksky]

I guess I'll need to tweak the speeds on my rollers

I have a magma version of what you've created, but my minecarts fly through the gaps quite frequently.

I made 10 carts and have 5 on either side of a 7 tile wide entrance path to spew doom onto invaders.

[Hetairos]

I guess I'll need to tweak the speeds on my rollers

I have a magma version of what you've created, but my minecarts fly through the gaps quite frequently.

I made 10 carts and have 5 on either side of a 7 tile wide entrance path to spew doom onto invaders.

I'm using 1 tile of max speed rollers and 4 impulse ramps, and the carts are going exactly as fast as they need to. There is a link to a minecart speed calculator at the bottom of the first post, you might find it useful for the tweaking.

Glad to hear someone is actually using this. So it works with magma in its current shape? Looks like I'll have to change the thread's title. How deadly are those contraptions? I don't have any invaders to test them on. Are you using rollers or impulse ramps in the "reload" section to push the carts back to the start?

[Ravendarksky]

I guess I'll need to tweak the speeds on my rollers

I have a magma version of what you've created, but my minecarts fly through the gaps quite frequently.

I made 10 carts and have 5 on either side of a 7 tile wide entrance path to spew doom onto invaders.

I'm using 1 tile of max speed rollers and 4 impulse ramps, and the carts are going exactly as fast as they need to. There is a link to a minecart speed calculator at the bottom of the first post, you might find it useful for the tweaking.

Glad to hear someone is actually using this. So it works with magma in its current shape? Looks like I'll have to change the thread's title. How deadly are those contraptions? I don't have any invaders to test them on. Are you using rollers or impulse ramps in the "reload" section to push the carts back to the start?

I am not using your design. I've independantly come up with something very similar. Next time I get a chance to play I'll fix my minecart speed issue and post results here. I wouldn't hold your breath though as my free time (for playing, not posting from work is extremely limited at the moment

[fricy]

There is a link to a minecart speed calculator at the bottom of the first post, you might find it useful for the tweaking.

Glad to hear somebody found it useful.