Binary cam
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]
Contents
Mechanics
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. Bowtech pays Rex Darlington of Darton Archery royalties for use of this cam design.
Comparison with twin cam
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Advantages
The binary cam system theoretically able to produce the highest arrow speed relative to its potential power.[citation needed].
Due to the symmetry of the system and the slaving of the cam design, once the initial timing is set, a binary system is resistant to coming out of tune, although this could happen if one cable stretches more than the other. Changes in limb or draw force will not cause the cams to be out of time.
Because of the slaving of the cams, variations in limb deflection force and vertical variations in grip pressure (drawing the string up or down instead of straight back) do not cause the cams to become out of sync.
Disadvantages
Binary cams require that both cams to be initially in sync with each other, by way of adjusting cable lengths, which may require the services of experienced bow shops to achieve. This can be done at any archery shop with a bow press.
Early binary cam systems were prone to cam lean. The cables hold most of the tension of the limbs, having this force non-centered put more load on one side of the limbs, typically the right side for a right handed archer, and causing the cam to lean. While this is true for any non-symmetrical cam system, it was especially problematic for some of the early three track designs where two cable tracks existed to one side of the string track.
