Construction of compound bow

The central riser of a compound bow is usually made of aluminium or magnesium. Many risers are made of the aircraft-grade 6061 aluminium alloy. Risers are designed to be as rigid as possible. The riser is the central mount for other components such as the limbs, sights, stabilizers and quivers.

Limbs are made of composite materialsand are capable of taking high tensile and compressive forces. The limbs store all the energy of the bow — no energy is stored in the pulleys and cables.

In the most common configuration, there is a cam or wheel at the end of each limb. The shape of the cam may vary somewhat between different bow designs. There are several different concepts of utilizing the cams to store energy in the limbs, and these all fall under a category called bow eccentrics. The four most common types of bow eccentrics are Single Cam, Hybrid Cam, Dual Cam and Binary Cam. However, there are also other less common designs, like the Quad Cam and Hinged.

Compound bow strings and cables are normally made of high-modulus polyethylene and are designed to have great tensile strength and minimal stretchability, in order that the bow transfers its energy to the arrow as efficiently and durably as possible. In earlier models of compound bows, the cables were often made of plastic-coated steel.

source : wikipedia