Crossbow Cam Synchronization for High Let-Off Accuracy
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Solution Overview
Problem
Crossbows face challenges in maximizing power stroke while minimizing overall length and width, leading to issues with projectile flight accuracy due to cam synchronization problems and excessive torque in high let-off designs, which affect shooting accuracy and archer comfort.
Innovation Solution
A crossbow design featuring rotatable members and cams with a reduced axle-to-axle length dimension, allowing for high let-off (up to 95%) and increased power stroke, while using lighter materials to reduce weight and stress on the trigger assembly, thus improving handling and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the axle-to-axle length dimension between limbs is reduced, then the overall width and length of the crossbow is minimized for easier handling, but the power stroke is limited reducing projectile velocity
Solution Approach 1:
The patent repositions the power cable attachment point on the limb to a location forward of the cam axle, utilizing the space in front of the traditional cam position. This dimensional repositioning allows the power stroke to extend beyond the cam axle location, effectively increasing the power stroke length without increasing the axle-to-axle width between limbs, thus maintaining a compact overall width while achieving greater projectile velocity
2Ease of operation
If high let-off is implemented to reduce archer fatigue, then archer comfort is improved, but torque and misalignment increase causing inaccurate projectile flight
Solution Approach 1:
The patent employs asymmetric cam profiles where the take-up track and payout track are intentionally designed with different geometries. The take-up track has a longer moment arm during the draw cycle to generate higher let-off for archer comfort, while the payout track is configured to minimize torque and keep the bowstring aligned with the shooting axis during release, thus maintaining shooting accuracy despite high let-off
Solution Approach 2:
The cam profiles are designed with variable parameters where the moment arm lengths and track geometries change dynamically during the draw and release cycles. The take-up cam has a longer moment arm during drawing to provide high let-off, while the payout cam adjusts its effective moment arm to minimize torque during projectile launch, allowing the system to optimize both archer comfort and shooting accuracy at different stages of operation
3Use of energy by moving object
If radically profiled cams are used to increase energy storage, then power stroke efficiency is improved, but cam synchronization problems cause erratic projectile flight
Solution Approach 1:
The patent introduces a synchronization mechanism that acts as an intermediary between the two cams. This synchronization device ensures that both cams reach their respective positions in the draw cycle simultaneously, preventing the timing discrepancies that cause the bowstring to be pulled off-center. The mechanism allows radically profiled cams to be used for maximum energy storage while maintaining reliable and consistent projectile flight through proper synchronization
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 mechanical efficiency, increases arrow launch speed, reduces maintenance requirements, and provides a more comfortable shooting experience with improved accuracy by minimizing unwanted forces on the projectile and reducing archer fatigue.
Implementation Method 1
Some crossbows utilize one or more cams which have progressed from simple variable leveraging units consisting of circular shapes mounted eccentrically, to more complex shapes that are intended to create more energy storage for a given power stroke.
Data Source
AI summary
In at least one embodiment, a crossbow comprises a stock, a first limb, a first rotatable member, a second limb and a second rotatable member. A bowstring, a first power cable and a second power cable each extend between the first rotatable member and the second rotatable member. The first rotatable member and the second rotatable member are constructed and arranged to provide a left-off during draw of said bowstring in an amount of approximately 70%, 80%, 90% or 95% or more. The drawstring let-off reducing load on a latch assembly and/or a trigger assembly.