Reduced Length Crossbow Midpoint Trigger Design
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Solution Overview
Problem
Conventional crossbows have a limited power stroke due to the design of the draw string and power cables, which restricts the rotation of cams to about 270 degrees, limiting the length of the power stroke and requiring larger pulleys that result in a less usable and larger bow.
Innovation Solution
A reduced length crossbow design with a trigger located near the midpoint and a small included angle of the draw string in the drawing configuration, featuring a string carrier that slides along a center rail to engage and retract the draw string, and a cocking mechanism that includes a rotating member and flexible tension member to achieve a power stroke of 10 to 15 inches with a small included angle of less than 25 degrees.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action 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 cam rotation is limited to about 270 degrees and larger pulleys are required resulting in a larger and less usable bow
Solution Approach 1:
The patent inverts the conventional draw string positioning by placing it on the up-range side of the string guides rather than the down-range side. This reversal allows the draw string to unroll between the string guides toward the target as the bow is drawn, enabling greater cam rotation beyond the traditional 270-degree limit while maintaining a compact bow size without requiring larger pulleys
Solution Approach 2:
The patent changes the spatial arrangement of the draw string from a conventional lateral positioning to a positioning that utilizes the up-range dimension. This dimensional repositioning allows the draw string to effectively unroll in the direction of arrow travel, increasing the power stroke length without increasing the lateral dimensions or overall size of the bow
2Power
If conventional crossbow design is used, then the structure is simple, but the power stroke is limited and kinetic energy generation is restricted
Solution Approach 1:
The patent introduces dynamic elements to the crossbow structure, including a movable string carrier that slides along the center rail and a catch mechanism that moves between engaged and disengaged positions. These dynamic components enable the draw string to be effectively repositioned and unrolled during the drawing cycle, significantly increasing the power stroke length and kinetic energy generation capability while maintaining reasonable structural complexity
Solution Approach 2:
The patent introduces a string carrier as an intermediary component between the draw string and the traditional string guide system. This string carrier serves as a mediator that facilitates the unrolling of the draw string between the string guides while maintaining control over the string's position and tension, enabling enhanced power stroke without excessive structural complexity
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
The design enhances the power stroke by up to 40% without increasing the diameter of the string guides, allowing for kinetic energy generation of over 70 ft-lbs with a power stroke of 8 to 15 inches, and provides a more compact and balanced crossbow with improved accuracy and usability.
Implementation Method 1
a flexible tension member, such as a rubber band, attached to the rotating member
Data Source
AI summary
A reduced length crossbow with a trigger located near a midpoint of the crossbow and a small included angle of the draw string when in the drawing configuration that creates a space between the draw string and the user's face. The included angle of the draw string when in the drawing configuration may be less than about 25 degrees. The trigger is typically located proximate the midpoint within about 10% of the overall length of the crossbow.