Crossbow Cam Rotation via Helical Cable Journals
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Solution Overview
Problem
Conventional bows and crossbows have limited power stroke due to the design of string guides and power cables, which restrict the rotation of cams to about 270 degrees, limiting the mechanical advantage and effective use of the bow.
Innovation Solution
A crossbow with a string guide system that allows greater rotation of the cams and pulleys by using helical power cable take-up journals and strategically positioned power cables, enabling rotation between 270 degrees to over 360 degrees, thereby increasing the power stroke without enlarging the bow's diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the draw string is positioned on the down-range side of the string guides to increase power stroke, then the power stroke length increases, but the power cables limit cam rotation to about 270 degrees
Solution Approach 1:
The power cable take-up journals are positioned in a direction away from the draw string journals, creating a spatial separation that allows cam rotation beyond the traditional 270-degree limit. This dimensional repositioning enables the power cables to be routed through a different spatial path, eliminating the rotational constraint while maintaining the increased power stroke length.
2Length of stationary object
If the diameter of the pulleys is increased to increase power stroke length, then the power stroke increases, but the bow becomes larger and less usable
Solution Approach 1:
The cam journals are designed to rotate through angles greater than 270 degrees (up to 360 degrees or more), dynamically extending the power stroke beyond the limits of traditional fixed-diameter pulley systems. This dynamic rotational approach allows the power stroke to be lengthened without increasing the physical diameter of the pulleys, maintaining a compact bow size.
Solution Approach 2:
Instead of increasing pulley diameter in the radial dimension, the invention extends the power stroke by increasing the angular rotation of the cams in the rotational dimension. The power cable take-up journals are positioned to accommodate this increased rotation, allowing the power stroke to be lengthened along the arc of rotation rather than through radial expansion.
3Volume of moving object
If the cam rotation is limited to 270 degrees to maintain compact bow size, then the bow remains usable, but the power stroke length is reduced
Solution Approach 1:
The cam journal is segmented into separate functional zones: a draw string journal portion and a power cable take-up journal portion. This segmentation allows the power cable take-up journal to be positioned in a direction away from the draw string journal, enabling independent optimization of each function. The power cable take-up journal can accommodate greater rotation angles without interfering with the draw string mechanism, thus extending power stroke while maintaining compact size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances the power stroke by up to 40% while maintaining a compact bow size, allowing for increased energy storage and arrow velocity without the need for larger pulleys or string guides.
Implementation Method 1
cams that increase the mechanical advantage associated with the draw of the bowstring
Implementation Method 2
bends the limbs toward each other to store the energy needed for the bow to fire the arrow
Implementation Method 3
Draw string 30 engages down-range edges 46A, 46B of string guides 22
Data Source
AI summary
A crossbow including first and second cams are mounted to first and second bow limbs, respectively. Each of the cams includes a string guide journal, an upper power cable take-up journal, and a lower power cable take-up journal. The draw string is arranged in a reverse draw configuration. The upper and lower power cables are received in each of the respective upper and lower power cable take-up journals and are displaced away from the respective draw string journals as the bow is drawn from the released configuration to the drawn configuration. In one embodiment, the upper and lower power cable take-up journals are helical in configuration. As a result of this configuration the cams can rotate more than 270 degrees, and preferably more than 300 degrees, as the crossbow is drawn from the released configuration to the drawn configuration.