How a Compound Works
A compound bow is a modern bow that uses a levering system, usually of cables and pulleys, to bend the limbs.
The pulley/cam system gives the shooter a mechanical advantage.The limbs of a compound bow are much stiffer than those of a recurve or longbow. This stiffness makes the compound bow more energy-efficient than other bows, as less energy is lost in limb movement. The higher-stiffness, higher-technology construction also improves accuracy by reducing the bow's sensitivity to changes in temperature and humidity.
The pulley/cam system also confers a benefit called "let-off". As the string is drawn back, the pulleys rotate. The pulleys are eccentric rather than round, and so their effective radius changes as they rotate. By the time the bow is at full draw, the change in pulley radius has approximately doubled the shooters mechanical advantage, and so less force is needed to hold at full draw. This "let-off" gives compound bows their characteristic draw-force curve: a quick rise to peak force and then diminishing to a much lower holding force. The exact shape of the curve is a function of the pulley geometry, which is a matter of buyer preference.
The pulley/cam system gives the shooter a mechanical advantage.The limbs of a compound bow are much stiffer than those of a recurve or longbow. This stiffness makes the compound bow more energy-efficient than other bows, as less energy is lost in limb movement. The higher-stiffness, higher-technology construction also improves accuracy by reducing the bow's sensitivity to changes in temperature and humidity.
The pulley/cam system also confers a benefit called "let-off". As the string is drawn back, the pulleys rotate. The pulleys are eccentric rather than round, and so their effective radius changes as they rotate. By the time the bow is at full draw, the change in pulley radius has approximately doubled the shooters mechanical advantage, and so less force is needed to hold at full draw. This "let-off" gives compound bows their characteristic draw-force curve: a quick rise to peak force and then diminishing to a much lower holding force. The exact shape of the curve is a function of the pulley geometry, which is a matter of buyer preference.