Tower cranes sometimes have very long booms, but seem to usually have fixed counter-weights at fixed positions behind the cab. Why doesn't it flip backwards when there is no load, or flip forwards when a load is way at the far outward end of the boom? It seems to be a very large range of moment arms given that the counter-weight has a fixed one.
I think the counter weights are connected to a pully system that directly interacts with the boom and hook movement. This way it can put more or less pull on the weights according to the amount of weight or position of the weight on the crane.
