Monday, June 11, 2018

On Pulleys

Only on the Hotspot: A post about how pulleys work. I've made at least one really bad call in-game about them previously. So here's my homework-atonement.

I've got a house rule in OED  that provides a small chance for a rope to break in any critical situation. My players totally hate it! (That said: I relaxed it a bit recently.) In dealing with this, sometime in the last year or two one of my players asked if they could purchase a pulley mechanism. I said, "I don't think that's available as medieval technology". Whoo-boy, was that super wrong. (If you have a mechanical engineering background you probably knew that.)
  • Pulleys have been in use since antiquity. Archimedes in the 3rd century BC studied it as one of the three most basic machines (lever, pulley, screw). Heron of Alexandria in the 1st century AD included it in his list of five basic machines (lever, windlass, pulley, wedge, screw), and described crane mechanisms using several pulleys. Renaissance scientists identified it as one of the six "simple machines".
  • Specifically in the medieval period, pulleys were used to hoist materials when building castles. Later drawbridge mechanisms used pulleys. They are part of the mechanism for a trebuchet. Some crossbows incorporated pulleys for cocking as early as the 13th or 14th century. On sailing ships they are referred to as block and tackle (although I couldn't confirm the earliest date of such use).
  • How much should one cost? Looking at the Medieval Price List, we can compare them to a vise, which seems like a machine of comparable sophistication (a large screw, basically). In the early 16th century this is documented at 13s 4d, or about 40 silver pieces in our silver-standard conversion of 1s = 3 sp groats. (In D&D book inflationary money, that might be 40 gp.) Note that if used for climbing or hauling, PCs would still need to find a solid structure to hang one on.

19 comments:

  1. As you are using the Medieval Price List... How much cost a rope in your games?

    The best source I found was this: http://web.mit.edu/21h.416/www/shippingtechnology/rigging.html#3

    Calculating for a more reasonable size, I think 50 pence (give or take) for 100 ft. of rope is a good call.

    Note: My own price table uses the 1-2-5 series of preferred numbers, all in pence.
    https://en.wikipedia.org/wiki/Preferred_number#1%E2%80%932%E2%80%935_series

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    1. By default, I just use the standard OD&D price list. E.g.: 1 sp for 50' of rope (Vol-1, p. 14). If I need to consult outside sources, I use a sp = groat conversion, that is, 1 shilling = 3 sp. More to come on that.

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    2. The calculations I'm doing based on that MIT page (assumes 3/8" thick climbing rope) are coming out to about one-quarter your price. Namely 0.56 shillings per 50' = 6.72p/50' = 13.44p/100'. So that might argue for 10p/100' in your system. More on that Thursday.

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    3. Thanks! I had a bit of trouble guessing how much length per kg a rope. I think I used the density of sisal (fiber rope)... Lets see on Thursday. :)

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  2. So pulleys can exist in our default pseudo medieval realm, but I wonder how bulky, reliable, practical they are to haul around a dungeon? A quick perusal of the links does give me something to wrap my head around. So at best I assume that Dwarves can make some quality ones about the size of what you see on the USS Constitution or similar vessel.

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  3. The cost and capacity of a pulley should absolutely rely on its size, which can vary wildly. Presumably the pulley adventurers might want to haul a chest of treasure up a well would be bigger than the one the villagers use to haul up a bucket of water, but smaller than one used in a trebuchet to help heave a half-ton stone across a siegeworks.

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  4. Thanks for putting this together. I looked into this a bit myself when converting an old Judges Guild tournament, the Corsairs of Tallibar, to a convention format a few years ago. The entry room to the dungeon has a shaft with an old block and tackle.

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    1. ^^^ "...Judges Guild tournament..." should read "...Judges Guild module..."

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  5. For what it's worth, I just checked out the price list for Gygax's post-TSR game Mythus, and they list pulleys for 5-25 bronze pieces (although it gives no parameters for weight capacity).

    For comparison purposes, 5 bronze buys a hacksaw, a jug, a quart of oil, a 10' pole, a small sack, or a waterskin. 25 bronze will buy a barrel, a pair of pants, a crowbar, a piglet, or a bolt of woolen cloth.

    I would assume that double pulley block you have in the picture up top would be mid- to high end of that range.

    It's weird what kind of thing will get your interest up....

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    1. Thanks for looking at that. That figure does seem underpriced to me... a pulley is clearly more sophisticated than a sack or a pole, for example.

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  6. In the 2e PH, a block and tackle is 5 gp and weights 5 pounds.

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    1. Interesting, thanks for checking that! (I'd argue it may be underpriced in that inflationary system.)

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  7. For something that cost a mark of silver, I assume that vise in the medieval price list is made of metal. I imagine a wooden pulley would be quite a bit cheaper, somewhere between 1 and 5 silver pieces (or gold pieces in the default D&D gold standard) depending on size.

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  8. What rule do you use to determine if a rope randomly breaks? And do you allow for skilled or experienced characters to check their equipment for signs of failure?

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    1. Here's the current rule: "Any sharp jolt is 1-in-20 to break a rope; increase for heat, moisture, or edges."

      I haven't to allow checking because (a) this is true even for new rope, and (b) I don't have any skills or specially-knowledgable classes in my OD&D games.

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