I was just as interested so I looked it up a little. The main design works with a large drum as a power source. The "control rope" is wrapped around a drum and

I was just as interested so I looked it up a little. The main design works with a large drum as a power source. The "control rope" is wrapped around a drum and connected to both the input and output. When the input applies torque, it pulls the slack out of the windings and pulls the rope tight against the drum. This frictional force applies torque to the output proportional to the input torque. The wikipedia article is pretty nice: https://en.wikipedia.org/wiki/Torque_amplifier https://en.wikipedia.org/wiki/Torque_amplifier Once you understand that, the Meccano version makes a little more sense. In this version, he experiments with several arrangements of the same principal. To use it in both directions, you need a drum and windings for each direction.