Crossbow Torque Control System for Extended Power Stroke
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Solution Overview
Problem
Conventional crossbows have limited power stroke due to the rotation of string guides being restricted by power cables, which limits the length of the power stroke and the kinetic energy generated, as the power cables stop the cam rotation at about 270 degrees, preventing further rotation and reducing the power stroke length.
Innovation Solution
A torque control system is introduced that includes a rotating coupling in the cocking handle, gears, and pawls to limit the output torque applied to the rotating member, allowing the draw string to be translated along a center rail from a released to a drawn configuration without further rotation, thereby increasing the power stroke and kinetic energy generated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If power cables are used to load the bow limbs and synchronize cam rotation, then the bow structure is stabilized, but the cam rotation is limited to about 270 degrees which reduces the power stroke length
Solution Approach 1:
The patent removes the power cables from the system entirely, replacing them with a direct draw string mechanism that connects the string guides to the limbs. This extraction eliminates the rotation limitation imposed by power cables while maintaining limb loading functionality through the draw string itself, enabling greater than 270 degrees of cam rotation and extending the power stroke length.
Solution Approach 2:
Instead of using power cables to load the limbs indirectly through cam rotation, the patent inverts the approach by having the draw string directly load the limbs while the cams serve only to guide the string. This inversion allows the cams to rotate freely without being constrained by power cable attachments, thus extending the power stroke.
2Length of moving object
If the diameter of pulleys is increased to increase power stroke length, then the power stroke is extended, but the bow becomes larger and less usable
Solution Approach 1:
The patent changes the fundamental parameter of how power stroke is achieved - not through larger pulley diameter but through increased cam rotation angle. By removing the power cable constraint and allowing cams to rotate more than 270 degrees, the system achieves extended power stroke (10-15 inches) while maintaining compact pulley sizes, thus avoiding increased bow volume.
3Length of moving object
If draw string is positioned on the down-range side of string guides to increase power stroke, then power stroke is extended, but cam rotation is limited by power cable contact
Solution Approach 1:
The patent extracts the power cable component that causes the harmful contact and rotation limitation. By removing power cables entirely and using the draw string for both positioning and limb loading, the system maintains the beneficial down-range positioning for extended power stroke while eliminating the harmful rotation constraint.
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 torque control system enhances the power stroke by up to 40% without increasing the diameter of the string guides, allowing crossbows to generate kinetic energy of over 125 ft.-lbs. with a power stroke of 10 to 15 inches, improving the efficiency and accuracy of the crossbow.
Implementation Method 1
A torque control mechanism limits output torque applied to the rotating member such that rotating the cocking handle after the string carrier is in the retracted position does not move the draw string past the drawn configuration
Implementation Method 2
at least first and second flexible limbs attached to a center rail and a draw string that translates along the center rail between a released configuration and a drawn configuration
Data Source
AI summary
A torque control system for cocking a crossbow. A cocking mechanism includes a rotating member mounted to the center rail and coupled to a flexible tension member attached to a string carrier. A cocking handle is configured to engage with the rotating member to cock the crossbow. A torque control mechanism limits output torque applied to the rotating member such that rotating the cocking handle after the string carrier is in the retracted position does not move the draw string past the drawn configuration.