Crossbow Cocking Rail Layout for Longer Power Stroke
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Solution Overview
Problem
Conventional crossbows with cams and pulleys mounted on the limbs are limited by the rotation of the string guides to about 270 degrees, reducing the power stroke length and dissipating energy, leading to inaccuracy and inefficiency.
Innovation Solution
The crossbow design features pulleys rotatably attached to the center rail or riser, with power cables connecting the limbs, allowing for increased rotation of the cams and power cable take-up journals, and a cocking system that moves a string carrier along the center rail to cock and de-cock the bow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving 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 is improved, but the rotation of cams is limited to about 270 degrees and the crossbow becomes larger
Solution Approach 1:
The patent inverts the conventional arrangement by positioning the string guides on the up-range side of the cams instead of the down-range side. This allows the draw string to unroll between the string guides toward the user while enabling greater cam rotation beyond the traditional 270-degree limit, thereby increasing power stroke length without requiring larger pulleys that would increase overall crossbow size.
2Length of moving object
If cams and pulleys are mounted on the limbs to increase power stroke, then the power stroke length is improved, but energy is dissipated by accelerating masses of the cams and pulleys
Solution Approach 1:
The patent extracts the cams and pulleys from the limbs and relocates them to the center rail or riser. This separation removes the rotating masses from the limb structure, eliminating the energy loss associated with accelerating these components during the power stroke. The power cables connect the limbs to the pulleys on the center rail, maintaining the mechanical advantage while preventing energy dissipation.
3Length of moving object
If cams and pulleys are mounted on the limbs to increase power stroke, then the power stroke length is improved, but the crossbow becomes less accurate
Solution Approach 1:
By relocating the cams and pulleys from the limbs to the center rail, the patent eliminates the instability and inaccuracy caused by moving masses on the limbs. The stationary mounting on the center rail provides a stable reference frame, ensuring consistent tension forces and improving shot-to-shot repeatability and accuracy while maintaining the extended power stroke.
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 length, improves accuracy by maintaining consistent tension forces, and increases the repeatability of cocking and firing, resulting in higher precision and efficiency.
Implementation Method 1
A one-way bearing may engage with the at least one screw shaft, the one-way bearing being configured to permit rotation of the at least one screw shaft in response to rotation of a cocking handle in a first direction to move the string carrier to the second position, and prevent rotation of the at least one screw shaft in a second direction
Implementation Method 2
A mechanical clutch may selectively disengage the one-way bearing and the at least one screw shaft to permit rotation of the at least one screw shaft in the second direction, wherein rotation of the cocking handle in the second direction moves the string carrier to the first position
Data Source
AI summary
A crossbow including pulleys rotatably attached to a center rail of the crossbow. Power cables of the crossbow connect the limbs of the crossbow to the pulleys. The draw string is enclosed in a safety cover. The crossbow includes a cocking system that translates a string carrier along the center rail to cock and de-cock the crossbow.