Editing Compound bow (section)

==Construction==

A bow's central mount for other components (limbs, sights, stabilizers and quivers) is called the riser. Risers are designed to be as rigid as possible. The central riser of a compound bow is usually made of [[aluminum]], [[magnesium]] alloy, or [[carbon fiber]] and many are made of [[7075 aluminum alloy]].

Limbs are made of fiberglass-based [[composite material]]s, or occasionally wood, and able to withstand high tensile and compressive forces. The limbs store the kinetic energy of the bow – no energy is stored in the pulleys and cables. Draw weights of adult compound bows range is between {{convert|40|and|80|lb|kg}}, which can create arrow speeds of {{convert|250|to|370|ft/s|m/s}}.

In the most common configuration, there is a [[Cam (mechanism)|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 using 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]].<ref>{{Cite web|url=http://www.huntersfriend.com/archery-help/compound-bow-guide-cam-technology.html|title=Compound Bow Cam Technology Explained - Hunter's Friend Archery|website=www.huntersfriend.com|access-date=2016-04-22}}</ref> However, there are also other less common designs, like the Quad Cam and Hinged. Cams are often described using their "let-off" rating. As a cam is rotated, the force required to hold the bow in position reaches a peak and then decreases as the bow approaches maximum extension (a position known as "the wall"). The percent-difference between the maximum force encountered during the draw and the force required to hold the bow in full extension is the "let-off". This value is commonly between 65% and 80% of the peak weight for recently designed compound bows, although some older compound bows provided a let-off of only 50% and some recent designs achieve let-offs in excess of 90%.<ref>{{Cite web|url=http://www.huntersfriend.com/archery-help/compound-bow-guide-cams-brace-height.html|title=Compound Bow Brace Height and Cam Specs - Hunter's Friend Archery|website=www.huntersfriend.com|access-date=2016-04-22}}</ref>

As the string is drawn the cam turns and imparts force to compress the limb. Initially, the archer has the 'short' side of the cam, with the leverage being a mechanical disadvantage. High energy input is therefore required. When near full draw is reached, the cam has turned to its full extent, the archer has gained mechanical advantage, and the least amount of force needs to be applied to the string to keep the limbs bent. This is known as "let off". The lower holding weight enables the archer to maintain the bow fully drawn and take more time to aim. This let-off enables the archer to accurately shoot a compound bow with a much higher peak draw weight than other bows (see below).

However, there are some youth-oriented compound bows with low draw weights that have no let-off and have a maximum draw length deliberately set farther than the majority of young shooters would reach.  This effectively makes the bow function very similar to a recurve, with the draw length determined by the shooter's preferred anchor point. This removes the necessity to adjust the bow draw length or use a different bow for different shooters (or to change bows as the shooter gets older). An example of this type of bow is the Genesis, which is standard equipment in the U.S. [[Modern competitive archery#Archery education|National Archery in the Schools Program]].

Compound [[bow string]]s and cables are normally made of [[ultra high molecular weight polyethylene|high-modulus polyethylene]] and are designed to have great tensile strength and minimal stretchability, so 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.