For big lifts, counterweights that weigh several hundred tons are attached to the base of the crane to prevent it from tipping over during lifts. The load is farther from the center pin than the counterweights. So to keep the crane upright, the counterweights need to be heavier than the load itself.
Counterweights actually need to be transported to the job site on trucks of their own. It would be impossible for a mobile crane to move with all that weight. Plus, building the crane on-site gives variability to how much counterweight is added to complete the project efficiently.
The weight of the crane itself also serves as a counterweight. So for smaller lifts, the crane may not need any supplemental weights. However, this is only true for small truck cranes that do not have an additional counterweight. Hydraulic all-terrain cranes travel with at least one load of counterweight by default.
Whether or not a lift requires additional counterweights, outriggers help to reduce the weight needed to keep the crane upright by distributing it over a greater distance. Outriggers are legs that extend from the base of the crane, lifting it off its wheels for added stability.
The boom isn't the only lever on a crane. When a lift requires a farther reach than the boom can provide on its own, operators can attach a jib to the end of the boom. There are two fundamentally different types of jibs: boom extensions and luffing jibs.
On some cranes, the jib is always attached to the crane. These are known as swing away jibs. On other models, a second crane lifts the jib into place so that it can be pinned to the boom of the primary crane. When used for this purpose, the second crane is referred to as an assist crane. It's not a unique design, just a smaller crane that happens to be lifting a jib on that day.
Once in place, boom extensions extend directly out from the boom. Luffing jibs, on the other hand, can adjust their angle mid-lift. You can see a luffing jib extending out from the boom of a mobile crane in the picture above.
The cables above and behind the jib are guy lines, which are used to change the angle of the luffer. And extending off the back of the boom is the mega wing, which provides support to keep the jib steady.
When the crane operator adjusts the angle of the jib, the far end of the jib moves a much greater distance than the point nearest the boom. The crane moves the jib by applying force to the end nearest the boom. Thus, it must apply a greater force over a shorter distance.
Booms and jibs are the best examples of how a crane uses levers to work. But if you're as smart as we expect you are, you've probably already noticed that cranes are more complex than hammers. Right you are! Cranes are complex machines, meaning they combine multiple simple machines into a single device.
