Crossbow Pulley Assembly for Lower Dynamic Launch Forces
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Solution Overview
Problem
Existing projectile launchers face design constraints due to heightened dynamic forces during operation, limiting the achievable projectile speed and force without adversely affecting accuracy or dimensions.
Innovation Solution
A crossbow design featuring a pulley assembly with rotatably coupled lever arms and pulleys that rotate independently of each other, reducing dynamic forces by allowing the draw string to move between released and drawn positions while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the degree of rotation of the cam is increased to maximize potential energy storage in the limbs, then the projectile speed and force are improved, but the dynamic forces experienced by various components during operation are heightened
Solution Approach 1:
The draw string system is segmented into multiple independent strands that are routed through separate pulleys. Each pulley can rotate independently, distributing the dynamic forces across multiple components rather than concentrating them on a single cam mechanism. This segmentation allows the system to handle higher forces while maintaining the ability to store sufficient potential energy in the limbs.
Solution Approach 2:
Pulleys are introduced as intermediary elements between the draw string and the limbs. These pulleys mediate the force transmission, allowing the draw string to move through a larger range of motion while the limbs experience controlled rotation. The pulleys reduce the direct mechanical linkage constraints, enabling improved projectile performance without excessive dynamic forces on the limb-cam connection points.
2Use of energy by moving object
If the degree of rotation of the cam is increased to store more potential energy, then the projectile launch performance is improved, but the design constraints on the projectile launcher are intensified
Solution Approach 1:
The system transitions from a static cam rotation mechanism to a dynamic pulley system where multiple pulleys can rotate independently during the draw and release cycles. This dynamic configuration allows the draw string to follow a more complex path that maximizes limb flexion and energy storage while distributing mechanical constraints across multiple moving components, thereby reducing individual component design constraints.
Solution Approach 2:
The draw string routing is extended into additional spatial dimensions by routing it through multiple pulleys positioned at different locations and orientations. This multi-dimensional routing allows the system to achieve greater draw lengths and energy storage without increasing the rotational demand on any single component, effectively adding spatial complexity to reduce mechanical constraint complexity.
Data Source
AI summary
A crossbow includes a flexible limb with a first end coupled to a frame and a second end. The crossbow includes a draw string that is configured to move between a released position and a drawn position. The crossbow includes a pulley assembly with a lever arm rotatably coupled to the flexible limb and configured to rotate about a lever arm axis. The pulley assembly includes a pulley rotatably coupled to the lever arm and configured to rotate about a pulley axis that is spaced apart from the lever arm axis by a fixed distance. The pulley includes a first and second draw string grooves. The draw string is received by the first and second draw string grooves. The lever arm and the pulley are each configured to rotate in a first direction as the draw string is moved from the released position to the drawn position.