Crossbow Cocking System Extended Power Stroke
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional crossbows have a limited power stroke due to the design of power cables and pulleys, which restrict the rotation of cams to about 270 degrees, limiting the length of the power stroke and kinetic energy output.
Innovation Solution
A cocking system with a rotating member and flexible tension member that allows for extended rotation of the string guides beyond 270 degrees by using interference members and a support shaft with recesses, enabling the power cables to wrap around helical journals and increase the power stroke without enlarging the pulleys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the rotation of cams is limited to about 270 degrees by power cables and pulleys, then the device structure is simple, but the power stroke length is limited
Solution Approach 1:
The support shaft is segmented with multiple recesses that receive interference members, allowing the rotating member to rotate through angles greater than 270 degrees while maintaining structural control. This segmentation enables extended power stroke without requiring a complete redesign of the entire mechanism.
Solution Approach 2:
The interference members are nested within recesses of the support shaft, and the rotating member contains a center opening that accommodates the support shaft. This nested arrangement allows compact positioning of components while achieving extended rotation beyond 270 degrees, increasing power stroke length without proportionally increasing device size.
2Length of moving object
If the diameter of pulleys is increased to increase power stroke length, then the power stroke increases, but the bow becomes larger and less usable
Solution Approach 1:
Instead of increasing pulley diameter in one dimension, the solution uses the interference members and recesses to enable extended rotation in the angular dimension. This allows achieving longer power stroke through increased rotation angle rather than increased radius, maintaining compact bow size while extending power stroke length.
Solution Approach 2:
The invention changes the operational parameter from pulley diameter to rotation angle. By using interference members that allow rotation beyond 270 degrees, the system achieves longer power stroke not by enlarging pulleys but by increasing the angular displacement parameter, thus maintaining compact dimensions.
3Ease of operation
If interference members are positioned in recesses to permit free rotation, then rotation freedom increases, but structural stability may be compromised
Solution Approach 1:
The interference members are designed to dynamically shift between engaging and disengaging states within the recesses. During cocking, they permit free rotation; during power stroke, they provide structural support. This dynamic behavior allows the system to adapt its characteristics based on operational phase, maintaining both rotation freedom and structural stability.
Solution Approach 2:
The interference members automatically engage with the inside surface of the center opening during rotation to inhibit excessive movement, and disengage to permit free rotation when needed. This self-regulating mechanism provides structural stability during critical phases without requiring external control systems, maintaining both rotation freedom and reliability.
Data Source
AI summary
A cocking system for retracting a string carrier on a crossbow that is substantially silent during operation.