Variable Length Bicycle Crank Arm for Mechanical Advantage
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Solution Overview
Problem
Current bicycle chain set mechanisms face limitations in increasing the length of the Pedal Lever Combination (PLC) due to ground clearance and average leg length constraints, restricting the mechanical advantage that can be achieved during pedaling.
Innovation Solution
A bicycle crank arm with movable sections that utilize electromagnetic forces to vary crank length during rotation, extending beyond top dead centre and retracting before bottom dead centre, allowing for increased mechanical advantage while maintaining adequate ground clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the Pedal Lever Combination (PLC) length is increased to gain mechanical advantage, then the force required to pedal is reduced, but ground clearance is compromised and the cyclist's leg length becomes insufficient to reach the pedals
Solution Approach 1:
The crank arm is designed with movable sections that can change length dynamically during rotation. The crank arm extends to a longer length when the pedal is in the downward position to maximize mechanical advantage and reduce the force required, then retracts to a shorter length when the pedal is in the upward position to maintain ground clearance and accommodate the cyclist's leg length.
Solution Approach 2:
The crank arm is divided into multiple sections that can move relative to each other. This segmentation allows the crank arm to change its overall length by extending or retracting the movable sections, enabling the system to optimize mechanical advantage at different points in the pedaling cycle without compromising ground clearance or leg reach.
2Productivity
If the Pedal Lever Combination (PLC) length is increased beyond fixed limits, then mechanical advantage is improved, but ground clearance during rotation is compromised
Solution Approach 1:
The crank arm transitions from a fixed length to a dynamically adjustable length. During the downward pedaling stroke, the crank arm extends to maximize the lever arm and mechanical advantage for propulsion. During the upward return stroke, the crank arm retracts to maintain adequate ground clearance, eliminating the harmful effect of ground contact while preserving productivity during the power phase.
Solution Approach 2:
The crank arm length changes periodically during each rotation cycle. The extension and retraction occur at specific phases of the pedaling motion, with extension occurring during the downward power stroke and retraction during the upward return stroke, creating a periodic variation in crank length that optimizes both mechanical advantage and ground clearance at different times in the cycle.
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 solution enhances the mechanical advantage by reducing the force required to pedal while increasing the distance moved proportionally, maintaining energy usage efficiency and improving the pedaling position for easier forward motion.
Implementation Method 1
The arm may comprise means for attracting and/or repelling the sections to/from each other, for example using magnetic forces. In some embodiments electromagnets are used.
Implementation Method 2
There may be provided an electromagnetic force to repel the two sections apart during the rotation of the bicycle chain set mechanism, and at times when the length of the PLC overcomes the present limitations and restrictions within the current system.
Implementation Method 3
The arm may be extended/retracted using a change in polarity and/or creation of polarity in either or both of a pair of opposing magnets (for example electromagnets), using the well-known effect to cause attraction/repulsion depending on the respective polarities of a pair of magnets.
Data Source
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AI summary
A crank arm for a bicycle chainset is provided. The arm comprises means for varying crank length during rotation, whereby to gain mechanical advantage.