Board Thread:General Discussion/@comment-31423496-20171104164922/@comment-28895263-20171105020402

I don't recall any canon source on this topic. But, as an engineer in real life, I've given it some thought over the seasons...

There are surely counterweights, attached to the lift lines and probably concealed by the guide tracks on either side of the lift cage. The power required to operate the lift is expended to overcome friction in the mechanism as much as in providing lifting power.

What kind of power? Wind, water, or muscle? I think it's water powered. Castle Black surely has a reliable source of water, Winter or Summer: a hot spring, or a river that never freezes. Some of this water is diverted through troughs to turn an overshot water wheel.

There would be two final troughs, selectable by the operator. Dump the water through the trough on the right to make the water wheel turn clockwise. Close that gate, open the one that directs water into the trough on the left, and the wheel turns counter-clockwise.

The wheel turns a capstan, the lift lines are wound around the capstan.

Nothing that can't be done with the technology that they have, and nothing that's inconsistent with what we've seen, and read.