for the wire i use a chain of ball constraints. between the first two there is a slider so that i can control the wire's length. the entities are invisible and the wire gets drawn with particles.

the disadvantage is that the first segment can get very long which doesn't look good. and the wire's length can't be shorter than about half of the crane height.

to avoid these disadvantages i tried to put a slider into every segment but it got very unstable then. maybe i will try out a solution with only three sliders. two at the end and one in the middle segment...