The binary cam is a design for the pulley system of a compound bow. Craig Yehle, director of research and development at Bowtech Archery, received a patent[1] for the design on December 11, 2007. Bowtech started equipping its bows with the new cam design in the 2005 model year.[2]
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The binary cam is described as a modified twin cam setup where each cam is slaved to the other via a loop of string connecting the two cams. This is contrasted with a typical twin cam setup where the ends of the bowstring are physically anchored onto each of the bow limbs.
As a twin cam system relies on each cam rotating independently, based solely on the force of the string and the resistance of the bow limbs being absolutely symmetrical, there is room for a twin cam system to "lose tune"[3] through wear and tear, string stretch, or just general age. The effect of a detuned twin cam bow is that the two cams rotate out of sync with each other, causing the bowstring to accelerate in two alternating directions upon release. This causes a number of adverse consequences, the most obvious being unsteady arrow flight.
The binary cam overcomes this by 'slaving' each cam to the other; as one cam is unable to rotate without the direct equivalent action of the other, the two rotate in near perfect synchronization, with any possible differences in rotation automatically correcting themselves as the shot cycle is completed. In effect, a binary cam bow never needs cam-timing tuning,[4] whereas a high end twin cam equivalent might need it done as often as every few months in order to maintain critical accuracy.
The binary cam system is able to produce the highest arrow speed relative to its potential power. This applies to binary cams as a theoretical system only, as binary cams are used on only one bow manufacturer, and bow design is equally integral to performance as cam design. A binary cam bow is not by definition faster than an equally powered bow of other cam type.
The binary cam system relies on interchange of modules to the cams to increase or decrease draw length, whilst many other bows may have their draw length altered simply by adjusting pin placements or tightening/loosening bolts. While modules can be changed at a bow retailer, it could pose as a potential problem for those wishing to sell the bow to another party, especially if the bow was verging on old or the design obsolete. It could also potentially prove inconvenient for those wishing to lend the use of their bow to another, i.e. on a group hunting trip.
Furthermore, there were significant numbers of reported limb failures on early binary cam models released by BowTech. However, it is not certain as to the cause of the failures.
Binary cams also require more specialised knowledge to tune, and may require the services of experienced bow shops to achieve. This demands a higher cost and maintenance.