Crossbow Cam Cabling System for Extended Power Stroke
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Solution Overview
Problem
Conventional crossbows have a limited power stroke due to the design of power cables that restrict the rotation of cams to about 270 degrees, limiting the length of the power stroke and kinetic energy generated.
Innovation Solution
The crossbow design includes flexible limbs attached to a center rail with cams that have power cable take-up journals allowing the power cables to wrap around and translate away from the draw string journals, enabling rotation beyond 270 degrees, increasing the power stroke without enlarging the pulleys, and securing the draw string to cross over the center rail.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If power cables are used to synchronize cam rotation, then cam synchronization is achieved, but cam rotation is limited to about 270 degrees which reduces power stroke length
Solution Approach 1:
The power cables are routed in a third dimension by passing them through channels in the center rail and using pulleys positioned above and below the rail plane. This vertical dimension allows the cables to wrap around the cams without crossing the center rail, enabling greater than 270 degrees of cam rotation and extending the power stroke length while maintaining manageable cable routing complexity
Solution Approach 2:
The cable routing is divided into separate segments: one cable segment wraps around the first cam while another segment wraps around the second cam. This segmentation allows independent optimization of each cam's rotation path and enables the cables to follow different spatial routes, achieving extended power stroke without excessive overall complexity
2Length of moving object
If draw string is positioned on down-range side of string guides, then power stroke is increased, but cam rotation is limited to about 270 degrees
Solution Approach 1:
The draw string is positioned on the down-range side of the string guides and routed through vertical channels in the center rail, utilizing the third dimension to achieve greater than 270 degrees of cam rotation. This spatial arrangement extends both the power stroke length and the duration of cam action without the cables limiting rotation
3Length of moving object
If pulley diameter is increased to increase power stroke, then power stroke length increases, but bow size becomes larger and less usable
Solution Approach 1:
Instead of increasing pulley diameter in the horizontal plane which would enlarge bow volume, the solution routes cables through vertical channels and uses pulleys positioned in the vertical dimension. This allows the power stroke to be extended through greater cam rotation angles without increasing the horizontal footprint or overall bow volume, keeping the bow compact and usable
Solution Approach 2:
The invention changes the operational parameter from pulley diameter to cam rotation angle. By allowing cams to rotate more than 270 degrees through clever cable routing, the power stroke length is increased not by making larger pulleys but by extending the angular range of rotation, thus achieving longer power stroke without increasing bow dimensions
Data Source
AI summary
A crossbow including first and second flexible limbs attached to a center rail. A first cam is mounted to the first bow limb and rotatable around a first axis. A draw string is received in string guide journals and is secured to first and second cams. The draw string unwinds from the string guide journals as it translates from a released configuration to a drawn configuration. Power cables are received in first and second power cable take-up journals on each of the first and second cams. As the crossbow is drawn from the released configuration to the drawn configuration the first and second power cables wrap onto the respective first and second power cable take-up journals and are displaced along the first and second axes away from the first and second planes of rotation of the first and second draw string journals.