An alternative to the pump stack, using less power and moving less magma. It is primarily intended for powering magma workshops, although you could run a magma weapon off it if the weapon recycles its magma or otherwise loses little to evaporation.
The design comprises three parts: the base section, the main section(s), and the top section. It takes exactly 100 units of power to run, and disgorges 2/7 magma approximately every 150 ticks. As an added bonus, in this particular orientation, all the machinery bar the lowest roller is at its default orientation. This exact design was an experiment to see just how much I could squeeze out of one one-wheel reactor, and is pretty bare-bones and does some odd things with physics to get that last level in.
If you want to try this, I highly recommend making a macro that carves a 2x2 circle (or square...) of track and then changes level.
# = Wall (some of these may not be necessary, as the cart stays on the tracks during sections in which there are no retaining walls)
← = Roller tile, west, highest speed (may obscure up ramp)
↓ = Roller tile, south, highest speed (may obsure up ramp or floor tile)
▲ = Up ramp, track
▼ = Down ramp, track
╔, etc. = Floor tile, track
X = Up/down stair
* = Gear assembly
o = Vertical axle
. = Open space
? = space for the mini-reactor. The exact placement of this is flexible, so long as it only takes one axle to connect to the rest of the spiral.
~ = magma entry point. As above, the exact location of this doesn't matter, though loading the minecart into the spiral will be easier if there's a wall to stop it overshooting the rollers.
! = magma dumps to here. The track stop one tile south is not shown, as it would cover the physics-abusing corner beneath.
Base section: 5 levels, 27 power (+21 here, for the mini-reactor)
z+4
#####
#╔↓*#
#▼#X#
#####
z+3
#####
###o#
#▲▼X#
#####
z+2
#####?
#▼↓*???
##▲X#??
#####??
z+1
#####?
#▲#o# ?
#▼#X# ?
##### ?
z0
#####
###*~
#←←←#
#####
The roller on z+2 has some issues 'catching' the minecart when it's approaching from beneath, causing the minecart to pause on the ramp before rolling downwards onto the roller and being boosted correctly. Extending the roller one tile to the south will stop it from rolling backwards, but here that would push the power requirement above 100. The westermost ramp on z0 is a NE track tile, and the roller will successfully push the minecart out of the magma despite it being set to push the minecart west and not north. This doesn't work so well if you're trying to push the minecart into another magma-filled layer and not an air-filled one -- on an earlier and larger design I couldn't get the minecart moved up to the next layer of liquid without having a correctly-oriented roller on the up ramp. Incidentally, you can power a NS roller directly off an EW one if they're built in a particular order (the one receiving the power through the front or back gets built first).
Main section (repeats): 7 levels, 13 power (x4)
z+11, etc.
#####
#╔↓*#
#▼#X#
#####
z+10, etc.
#####
###o#
#▲▼X#
#####
z+9, etc.
#####
##▼o#
##▲X#
#####
z+8, etc.
#####
#▼▲o#
###X#
#####
z+7, etc.
#####
#▲#o#
#▼#X#
#####
z+6, etc.
#####
###o#
#▲▼X#
#####
z+5, etc.
#####
##▼o#
##▲X#
#####
This part is pretty simple, and the one you repeat when you extend the cart spiral. Highest-speed rollers
can push a minecart one level further than the seven used here, but you lose much more than you gain because you can't have the power coming from a 1x1 column of gears and axles any more.
Top section: 8 levels, 0 power
z+40
!
###╗#
#▼═╣#
###.#
#####
z+39
#####
#▲#X#
###X#
#####
z+38
#####
###X#
#▲▼X#
#####
z+37
#####
##▼X#
##▲X#
#####
z+36
#####
#▼▲X#
###X#
#####
z+35
#####
#▲#X#
#▼#X#
#####
z+34
#####
###X#
#▲▼X#
#####
z+33
#####
##▼X#
##▲X#
#####
This is the silly part. Rollers can push a minecart up eight levels, but barely, and the winding track that leads the minecart to the return chute will rob the minecart of its remaining speed. The sane thing to do would be to knock a level off the top of the design. Instead you throw the minecart into a wall, where its momentum pushes it north into the corner tile. The corner tile not only slows the minecart down, but pushes it back with just enough force to move it two tiles south and over empty space, where it falls. Most of the time I find that one level of open space is enough to make a minecart fall through stairs, but in this particular case it can come to a stop on the stairs, possibly because it was moving so slowly when it started falling. More levels of open space will solve that problem.
Good points:*Small footprint
*Requires few materials
*Requires little fuel / heat
*Low impact on FPS
*Low power requirements
*Most components either made of raw stone or available from traders cheaply and in reasonable amounts
Bad points:*Slow
*Low-output
*REQUIRES magma-safe materials: one minecart, two mechanisms, and one chain. (That's all, even for the parts that get exposed to magma mist.)
*Requires large amounts of wood
*May cause numerous workplace accidents
The footprint can be reduced further by skipping the access stairwell and using the power train as the return chute, but that costs extra power and a second magma-safe roller, and you'll run into access issues when placing the axles. You can also install a pump at the magma level to keep the magma in z0 topped up, and install a lever-linked hatch somewhere in the drop chute to act as an off switch. Bridges are risky as they give horizontal momentum to dropped objects or creatures, and that may throw the minecart onto a tile it isn't moved from automatically.
A rather pressing safety issue is that the minecart is not associated with a route or being deliberately moved between stops, so dwarves will happily run into the spiral and either successfully take the minecart away to a stockpile or get horribly mown down by it, or dodge into the return chute or run into magma mist. You can put the hatch somewhere where the minecart can't be touched even if it does get accidentally unforbidden, but I don't think anything short of cutting off their pathing will stop them chasing after it when it's in motion.
If you want really small amounts of magma for shallow magmaworks, it's probably less hassle to make some minecarts, drop them in magma, recover them and haul them from the deep, and then dump their contents into a bunch of little pits in the workshop area.