The link vapochilled provided is excellent. The "ropewalk" described therein is undoubtedly excellent and efficient. It's also more sophisticated than it needs to be.
I made mine (actually several; they tend to disappear between rigging jobs) out of a Lego set. Lego makes nice gears, and the blocks with holes in them make good, smooth bearings for the shafts. I've never bothered motorizing a ropewalk; I just turn the gears by hand. (I tend to work on small scales, so the ropes I make don't need to be long. Quite a few years ago I did a Heller
Soleil Royal; the main topgallant backstays for it started out as three lines stretching across my basement, and required, if I remember right, about 45 minutes of cranking. If I were doing a project that big again I'd probably invest in a motor.)
The great thing about ropewalks is that if they work at all, they work right. A ropewalk needs four features: a set of three gears on one end, a gadget at the other end to spin the three strands into one, a "top" in the middle to control the pitch at which the strands intersect, and a means of making the whole arrangement shorter as the rope is made. Anything beyond that just makes the job go faster - and costs additional money.
One more thing to bear in mind - especially if what you're working on is that little Revell
Flying Cloud. A ropewalk does two things for you: it lets you make rope of particular diameters, and it gives you the option of spinning it up in either direction (cable-laid or hawser-laid). If you think about it carefully you may conclude that neither is particularly relevant to this particular project.
Almost all commercially-availabe thread is hawser-laid (i.e., spun up right-handed). For models of ships prior to the mid-nineteenth century that's problematic, because such vessels often used cable-laid (left-handed) rope for their standing rigging. By the middle of the nineteenth century, however, cable-laid rope had almost disappeared. It's a safe bet that all the line used in the
Flying Cloud was hawser-laid. So ordinary thread can represent it accurately.
Model Expo ( www.modelexpoonline.com ) sells quite a variety of line in appropriate colors and diameters for ship model rigging. My suggestion would be to see whether Model Expo can provide everything you need, without recourse to a ropewalk. My guess is that it can.
Two golden rules about ship model rigging: 1. If in doubt regarding size, err on the small side. 2. If in doubt regarding color, err on the dark side.
Hope this helps a little. Good luck.