When the need arises, and the technology is available, it often happens (as with the motor car) that several individuals become interested quite independently of each other in trying to improve or develop a machine or weapon. This was probably the case in various parts of Asia four or five thousand years ago, when a recipe for a good fish glue might perhaps have been the technology needed to initiate experiments by bowyers in different tribes.
So it was in the USA, in the early 1960's, an enormous surge of interest in bowhunting creating the need, modern glues and fibreglass the technology. With a multitude of bowhunters, many of whom were engineers, it was perhaps inevitable that a number of them would experiment with devices to improve the efficiency of the bow.
One such was a keen bowhunter, Holless Wilbur Allen: he was also a very able mechanic.
Early in 1961, at his home in Missouri, he would have been excited at the unveiling, by the nearby Hoyt Archer Company, of the 'Pro-Medalist', the first bow to be fitted with torque stabilisers (an innovation which was to have as profound an effect on the appearance of the target bow as the invention of television to the outline of chimneys of the family home).
Perhaps stimulated by the new Hoyt bow, and with vague memories of school blackboard chalk drawings such as this:-
Wilbur Allen had an idea: what about attaching a pulley to each bow limb, to create a block-and-tackle effect? Using limbs sawn off a recurve bow and ordinary pulleys with a central axle, he built an experimental bow; but, disappointingly, the draw length was very limited owing to the short distance travelled by the limb tips.
However, during a further four years' experiments, he tried cam-shaped pulleys, and also circular pulleys with the axle off centre ('eccentrics') and found that as the string unwound, a draw length sufficient for normal length arrows was obtained. But also, there was an astonishing bonus! The draw weight reached it's maximum half-way through the draw, with a much reduced pull required to hold the string at full draw! This was exciting, but even more so was the astonishing cast of the new bow !
From January to June, 1966, he refined his design, and on June 23rd. 1966 he filed an application for a U.S. patent. It was accepted, and eventually granted in December 1969. Several other archers had been experimenting with similar devices, but apparently with less advanced results: The patent application was for 'An archery bow with drawforce multiplying attachment'. It should be said that the two sheets of drawings showed a bow that was to all intents and purposes an 'archery bow', but with the bow limbs attached to the handle riser with adjustable bolts. The bow limbs were also unusually thick, and each had a V-shaped slot at the tip. So, what were the 'attachments'?
Two alternatives were shown on the patent drawings: a cam-shaped pulley was featured on the bow which appeared on both sheets, fixed in the V-shaped slot at each limb-tip, the second sheet depicting the cam at various stages of the draw; but also on the second sheet was a detailed drawing of an eccentric wheel as an alternative to the cam. The sectional drawings showed both cam and eccentric wheels to be quite narrow. The string was led around the cam or eccentric, to be attached to the opposite wheel axle, therefore three times as long as an ordinary string.