The baby that got orphaned at two weeks finally hit his first birthday, so i finally could stop the regular "remove hunger/thirst" raw re-edits. I generally just switched eating and drinking off whenever Likot was dangerously in need and switched it back on thereafter, so the rest of the fort could eat and drink at least a bit. Miraculously enough, Likot received water _twice_ in that year, but food only once. The second gift of water was had after another NO_DRINK update, i.e. the job was generated in the tiny time window between unpausing and the thirst reset, in the split second when Likot was a thirsty unit with the NO_DRINK flag.
I formulated the basic concept of the unjammable speedy minecart grinder.
It's well-known that very small perpetual-motion grinders are possible, but they won't gain much speed: the smallest design is this:
#▲▲# #══#
both ramps must be unusable, i.e. with ceiling directly above or walls on top of the surrounding walls. There's also a four-impulse-ramp design, but it does nothing fundamentally different from this one - the cart accelerates "down" the ramp it is on, bug-teleports "up" the other ramp, bumps into the wall and accelerates in the opposite direction.
Why don't i use this grinder design? Because it's laaaame. The cart spends eight steps on each tile, i.e. it moves quite sluggishly.
For a speedy powerless grinder, you need to take the corners on proper corner track, without the abrupt, speed-nullifying wall bumps in all-impulse-ramp designs. You can do this by using flat corners:
#║##
#╔╗# #╔╗#
#▲║# #╗║#
#▲║# #╗║#
#▲║# #╗║#
#╚╝# #╚╝#
#+##
with optional input/output connections - push track from the north, lever-operated (or invader-opened) door to the south. Cart cycles counter-clockwise.
A nice railgun design, since it achieves maximum ramped speed. It's less useful if you want invaders to walk through it, because if the cart stops on flat track, it'll stand still, putting the grinder out of operation until it's re-set and restarted, which usually requires getting the invaders out first, and the non-operational grinder no longer helps getting rid of them.
If the cart stops on a legal ramp, however, it will keep accelerating, bumping into and sometimes running over the creature blocking its path. But to do this, we need to take corners on legal corner track _and_ on a proper ramp. I.e., we need to change z-level.
##+## ##+##
#▲#▲# #╔#╗#
#▲#▲# #╗#╚#
#▲#▲# #╚#╝#
##+## ##+##
z+1
##### #####
#▼▲▼# #▼╗▼#
#▼#▼# #▼#▼#
#▼▲▼# #▼╚▼#
##### #####
Cart moves counter-clockwise.
The up/down ramps in the corners allow the cart to take the corners without losing all speed, the impulse ramps on the upper level are absolutely required: carts coming from flat track will only take a down ramp if they're going at less than derail speed. They will take the ramp if they're already coming from a down ramp, which _can_ be an impulse ramp.
The impulse ramp on the lower level, between the down and the next up ramp, is also required, to give the cart a sufficiently straight trajectory so it takes the next corner properly. Down and up ramp immediately adjacent do _not_ work. The cart will circulate, but it keeps bouncing back and forth once per round, stopping and starting again and wasting ~30 steps.
This minimal design still doesn't provide much speed: it takes 65 steps for 6 full rounds. Yes, it's not a per-cycle period, the pattern shifts through various positions; five rounds will take eleven steps each, the sixth will only take ten. Of course, it still moves eight tiles in ~10,85 steps, meaning it's on average above derail speed.
The basic design can be expanded by adding more impulse ramps. It doesn't seem to matter whether those are added on the lower or upper level, i usually opt for extra ramps on the lower level, since those offer an easily viewable layout for an actual grinder, using doors where they're shown above.
The funny thing is that for the first four expansions, the circulation time stays exactly the same (i.e. the exact six rounds in 65 steps). The layout below will cycle at the same rate as the minimal design, but the cart's about twice as fast:
##+## ##+##
#▲#▲# #╔#╗#
#▲#▲# #╗#╚#
#▲#▲# #╗#╚#
#▲#▲# #╗#╚#
#▲#▲# #╗#╚#
#▲#▲# #╗#╚#
#▲#▲# #╚#╝#
##+## ##+##
(with the usual connecting impulse ramp on the level above - not shown)
Expanding it by one more ramp pair will finally break the pattern - the cart'll take twelve steps precisely per round.
Carts will keep hold of their cargo while in such a cycle, but will typically jettison it when colliding with a heavy creature. The grinders can also get clogged by large creatures like trolls and forgotten beasts - they'll keep hitting and hurting them, but can't move past the creature until it dies or dodges out of the way.
To stop operation, a retracting bridge on one of the corner tiles should be used. Carts can be inserted via hatch from above - this also gives trolls and other building destroyers a nice target, to keep them in the grinder.