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I'm working on a low tech setting for a fantasy story. I'd like to see how far I can get operating within the laws of physics (no magic, gunpowder, or steam-powered devices) but still produce interesting solutions to engineering problems.

For example, I'm thinking a continent-spanning empire could benefit from a network of rails originating from a capital city in order to quickly move armies to quell rebellions.

Given a proper gradient to overcome friction, could an unpowered railcar starting at high altitude (say a high mountain) roll along a track for hundreds or even thousands of miles without stopping?

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    $\begingroup$ Even if the answer is "yes", how do we get the car back up the hill? $\endgroup$
    – Alexander
    Sep 9, 2021 at 18:41
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    $\begingroup$ As for the question itself - not with the gradient of 1/100 (or smaller) and real world friction. Yes with maglev or similar frictionless technology. $\endgroup$
    – Alexander
    Sep 9, 2021 at 18:53
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    $\begingroup$ You might find it worthwhile to read many of the stories set in the universe of Eric Flint's 1632. $\endgroup$ Sep 9, 2021 at 19:07
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    $\begingroup$ What is your technology level exactly? You have iron/steel works, advanced bearings, and are able to produce enough to build a railroad and some sort of railcar, all industrial revolution inventions, but you're still calling it low tech? And for some reason pulling it with animals isn't an option? $\endgroup$
    – Mathaddict
    Sep 9, 2021 at 19:58
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    $\begingroup$ The underlying question is how there's enough metal for a rail network without having Industrial Revolution level of mining tech (which includes steam powered mine pumps) and ore refining. AFAIK, historically, wooden rails didn't last very long. Anyway, it might be worth looking to Sean McMullen's "Souls in the Great Machine", which did describe human pedal-powered (!) trains, where both a dedicated crew and, optionally, passengers pedaled to move train cars along a track. $\endgroup$ Sep 10, 2021 at 3:05

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Your empire can have a network of canals.

  1. No steel needed.

  2. A lot more work to cut a canal than a rail. Ditto for derailing a barge.

  3. Animals can pull barges along the canal, like they do. Bargemen (and women!) can sing songs, sometimes about the animals. Like the good old mule whose name is Sal.

  4. Unpowered barge coming down canal from altitude is much more exciting. You can cry havoc! and let slip the barges of war. Maybe there could be cameras to take your picture on the way down.

  5. "Warbarge Ascendant" will be the name of the second book in your series because they have to get the war barges up back to the top.

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    $\begingroup$ Locks are a very old technology. $\endgroup$
    – Mary
    Sep 10, 2021 at 1:17
  • $\begingroup$ Thank you - agreed that canals are a proven technology with both animal and wind power. Manufacturing steel in a pre-industrial setting is a big hurdle if rails are to be built. Keep in mind the Song Dynasty of medieval China was more than capable of producing prodigious amounts of iron & steel without steam power. The Chinese Empire is an inspiration here - but turned up to 11. :-) $\endgroup$
    – RobertF
    Sep 10, 2021 at 14:07
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    $\begingroup$ Canals are great for shipping goods, however, "quickly move armies" is not something that was done via canals. $\endgroup$
    – Alexander
    Sep 10, 2021 at 16:35
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One gravity based option would be to have regular stops along the track where a massive weight could be rolled onto the top of a small tower on an "engine" carriage. The weight would force down some sort of connected geared mechanism that drove the wheels. As the weight slowly sank down it would propel the train forward. At the next station the old weight is rolled off and a new one is rolled on much higher up.

Each station would need a means of raising the weights up either by human/animal labour or perhaps aided by water power if available. Long down hill stretches could also be incorporated.

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  • $\begingroup$ +1 Very clever, I hadn't thought about using weights to spin up the wheels of the railcars. And it wouldn't have to be a single massive weight that's lifted - a bunch of smaller weights could be lifted using conscripted labor or animal power. $\endgroup$
    – RobertF
    Sep 10, 2021 at 14:23
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    $\begingroup$ True. Could even be water if available or it could have a "mixed fuel" capability $\endgroup$
    – Slarty
    Sep 10, 2021 at 15:41

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