It may be the case that we have no need to form any kind of mechanical advantage using a pulley system.
In the example below we have a small load weighing 10kg. The load only needs to be lifted to a height of 1.0m but due to the nature of the environment the effort required to lift the load will need to be applied from a remote point. We could easily go all in and attempt this without any pulleys.
We seem to be getting there but we do have a problem. At any point where the rope comes into contact with the edges of the tunnel there is a huge amount of friction caused by the rope running over the surface. Not only will this require a larger input effort to be applied but as we’re using a soft textile rope we can’t expect this system to hold up for very long before the rope gives up and breaks!
All we need to do is to construct a system that uses pulleys to change the path of where the effort needs to be applied. To do this, firstly we need to connect the rope to the load that requires moving. Secondly we need to give the rope a route back to where the input is going to be applied, avoiding contact with the edge and surfaces.
Due to the bends within the structure we are going to install a few pulleys into the system. By adding the pulleys we are reducing the amount of friction within the system, making it easier for the operative to move the load and also protecting the rope from the abrasive edges of the tunnel.
The 1:1 Redirect
The amount of effort required to lift the load in this situation is 100kg so we have not formed any mechanical advantage. This system has a ratio of 1:1, additionally for every metre of rope that the user pulls through the system the load will be raised by a metre.
All this system does is change the direction of where the effort needs to be put in, instead of pulling the rope in an upwards direction it can now be pulled downwards which is usually more efficient. This is commonly referred to as a directional or redirect pulley.
In this situation the directional or redirect pulley and its anchor point will actually be feeling double the weight of the load, as there is the loads weight on one side and an effort of 100kg needs to be applied on the other side to raise the load.