Oh, and they are DEFINITELY not safe. Despite being extremely careful, fully armored, megabuffed, and way more durable than an ordinary dorf I still ended up with a mangled lung at one point, mushed guts, smashed open arms and legs, and this is just from the carts whacking into me. Wouldn't survive slamming into a tree or wall very well.
But yeah, don't think dfhack is updated, I just changed the carpenter reaction from making a spear or whatever to making a minecart. I was using candy because I was trying to cast obsidian structures and magma is damn heavy, but then I saw how fun bouncing them off these bandits was so I switched it to spit out steel instead of whichever log I fed it. (Just left the green glass furniture from the hyperdecay bug cause it's pretty.) Though some of them were found in various tombs and whatnot, the iron one I was riding up at the top is why I whipped up the steel ones.
Oh, I actually started playing with them today because I was trying to fill a river flood plain and it was slow with just the normal water pressure so I screwed around setting up a watergun.
I found a little river junction/shallow waterfall with a paved highway right beside it.
So I needed magma to shut off the subsurface flow to make the upper dam matter, and so the bottom floor would be below the water level.
Then I walled off the part of the highway that would get flooded and ended up putting a vaulted roof over it because the spot just craps lumber left and right.
Though I figured that I would need to do my usual routine to get magma: head to a volcano, swim down inside (I'm way beyond fireproof, a dorf is just a dwarf shaped version of my steelbone flying deity-posing dragons without firebreath, ultimately), find a candy cane and use that as a surface to drop the cart on, letting it get filled, and repeating til I get down under 1.0 speed or so.
Apparently Toady noticed you could fill a minecart with lava the same way you can with water, so, bleh.
BUT!
If you happen to have some rock flooring or rock walls and deconstruct them (which works fine, thankfully) you're left with a unit of magma. If you quickly pick it up before it cools/disappears/whatever happens, you can put it into a minecart, and when you dump out a minecart it makes a pool which can then be used to refill that minecart up to 833 units of magma, which goes to show that minecarts are so awesome they defeated
math!
I set up a cistern and used it to seal up my dams.
Then when I got everything set up in the flood plain I removed part of the eastern dam to begin filling it.
It took a while though so at first I thought to try out a bucket chain method, filling the minecarts and dumping them on the low side, but that is tedious.
Sitting inside a cup with 2 tiles of 7/7, keeping it refilled with minecart magic and slamming another minecart into the wall to shoot the water where I wanted it to be? Much less tedious.
Unfortunately if you shoot too many shots in a short period of time like this and keep on using the minecart magic to refill the water it inevitably segfaults the game. So I tried to lengthen the barrel to space them out.
It worked but the carts piled up a little bit since it wasn't long enough, and when I started to lengthen it, it wound up looking like some sort of buck rogers ray gun, so I went with it.
Sadly running it at full tilt conspired with the water movement already taking place to cripple my framerate in camp.
That was annoying so I went and set up a wall and refilling cup by a bandit camp (you can see it in the "practice" gif) which was a lot of fun and surprising effective, I ended up going over there to finish off the last three or four when I got the idea to ride the cart at them, and then launching the carts while riding so I could pretend I'm a GOU Abominator from the Culture.