Hi there, intresting thread, I was thinking about the same thing, and I'd like your opinion on what I came up with:
In my next fort I want to build something similar, but a bit more reusable: a double helix - powered minetrack system that can go from any floor to any floor...sort of.
You can see the basic setup on the attached picture, the double helix is a loop in on itself as the two ramps connect at the very top and the bottom, rollers are installed on every second floor, and you need about 5-8 power/level to operate it depending on what you want to build it with: axles or mechanisms. Plus the additional scaffolding, and the minecart logic system to drive the whole thing...so yeah, that's a lot.
I use newton's cradles for control in the prototype I built, but a simple ramp based can work I guess.
There is one logic circuit per ride, (SYS) and one central logic piece, the loop system (LOOPSYS). It's function is to keep every green door closed when a cart is in the spiral, not because of collision, but to make sure that carts exit where they should.
The system looks like this: (let's take a ride from lvl20 to lvl1.)
When a dwarf finished loading a cart from the stockpile (TS) on lvl20, it's pushed towards the roller. If the spiral is in use by another car the green door is closed, so the cart goes into a loop. When the door opens, the cart activates the first pressure plate (PP1), which signals the hauling route's minecart logic (SYS1). SYS1 turns on LOOPSYS and opens the The dark blue door on lvl1 and the orange door on lvl20 (and any other doors that may be on the way.) The minecart makes the round, autodumps it's contents, returns and resets the system with PP2.
The beauty of the system is that it works as long as two different colored doors are opened, (at worst case you travel the helix twice,) you can add more destinations easily to a ride (for eg. food dsitribution to a new block?), and you can reuse an existing ride by connecting a different helix-door and modifying the hauling route - great if you move your stripmining operations to a different level.
It's possible to design advanced switching logic to let more than one cart use the structure, but that task is for another day, as the ride in the spiral + the potential wait in the loop should be negligible compeared to the time it takes to load a cart. (with the obvious exception being water and magma, which lines need a delay timer built in so other carts do not get stuck in a loop.) You can exit the spiral on every second level, but it's pretty easy to reach any level on the map with 2 additional ramps.
EDIT: If you use different materials for the carts, set up the PP2 plates with the weights accordingly, and add a door operated by PP2 to the return side to only let the proper cart in, then you can launch multiple carts into the helix at the same time. The launching loop is not needed, that's also one less logic circuit. The number of routes is limited by the number of minecarts with different weights. 11 routes with vanilla metals plus the woodtypes. hmmm....
One thing I want to use it is to transfer magma to a reservoir at the top, that can be repurposed with a single lever into a magma catapult device. The idea was to have 5 carts with the same program in a row, and gchristopher's pump-roller design is genius for that, thx, I'm going to use that!
Otherwise I have yet to come up with a general fort/stockpile design to take advantage of this system so it's actually useful, and not just a gimmick, so I can say I can juggle 20 minecarts around at the same time.
So? Any thoughts?
PS: What do you use to format your code into this compact form? I tried pasting in code from excel/.csv files, but the formatting i get is unreadable.