Zip Line Trolley
The zip line trolley is the frame or assembly together with the pulley(s) aka sheave(s) inside that run along the cable. (The term "trolley" is more often used when this assembly consists of more than a single pulley with simple hanger and bearing.) Often more than one pulley is used to spread the load over more than just one spot on the cable and reduce cable bending stresses that may lead to metal fatigue and cable breakage. This also reduces any tendency of a pulley to twist sideways and run up and off of the cable with obvious disastrous results. In addition, the trolley is usually shaped or has protrusions or parts to hold the cable in the groove(s) of the pulley(s).
A pivoting link, such as a carabiner, is used to secure the load to the trolley so that the trolley does not have a tendency to rock in a manner that it may fall off of the cable if the load should sway. Load carriers ranging from enclosed cabins to gondolas to harnesses are attached to the link. Occasionally the load carrier is just a handhold or handlebar although there is the danger of the rider's losing his grip and falling. Such a simple carrier should only be used on zip lines that are low to the ground or over water.
Some zip lines are used for transportation while others are purely for recreation and amusement.
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