Differentially Biased Pedal Transmission for Low-Center Stability
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Solution Overview
Problem
Existing human-powered vehicle designs face challenges in achieving a low center of gravity, ergonomic comfort, and efficient power transmission, often requiring compromises in biomechanics, stability, and durability due to the use of rotary or oscillating input systems with over-run clutches and flexible components.
Innovation Solution
A mechanical transmission system utilizing a rocker-driven crank mechanism with alternatingly biased connecting rods and spring-tensioned cables, eliminating the need for limit stops and over-run clutches, to transform oscillating motion into continuous rotary motion, maintaining a low center of gravity and enhancing ergonomics and maneuverability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional pedal crank arrangements are used, then power transmission is achieved, but the crank spindle must be located at significant height above ground compromising stability and ergonomics
Solution Approach 1:
The patent inverts the traditional crank mechanism by placing the rockers at the bottom near ground level instead of positioning the crank spindle high above ground. This inversion allows the pedal axis to be located low, improving stability and ergonomics while still achieving effective power transmission through the rocker-crank linkage.
2Power
If over-run clutches and one-way bearings are used to rectify output rotation, then rotary motion is achieved, but torque and life cycle limitations are imposed
Solution Approach 1:
The patent extracts and eliminates the over-run clutch and one-way bearing components from the system. Instead of using these fragile components to rectify rotation, the invention employs a symmetrical dual-rocker mechanism where both rockers contribute to forward rotation, achieving reliable rotary output without torque-limited clutches.
Solution Approach 2:
The dual-rocker mechanism ensures continuous useful action by having both rockers drive the crank in the same rotational direction throughout their strokes. This eliminates the need for rectification mechanisms and maintains continuous power transmission without interruption or reliance on limited-life clutch components.
3Power
If flexible fins are used in oscillating input devices, then motion transformation is achieved, but service life and durability are compromised in high torque environments
Solution Approach 1:
While the patent acknowledges flexible fins are used in prior art, it replaces them with rigid rocker arms and connecting rods. This substitution of flexible components with rigid mechanical elements significantly improves service life and durability while maintaining the oscillating-to-rotary motion transformation function in high-torque environments.
4Ease of operation
If limit stops are used to define reciprocating stroke, then motion control is achieved, but equipment damage can occur and operator manipulation is required
Solution Approach 1:
The patent employs a dynamic geometric constraint system where the rocker arms are connected to the crank through fixed-length connecting rods. The stroke limits are naturally defined by the geometry of the linkage and the rotation of the crank, eliminating the need for rigid limit stops while preventing equipment damage through inherent mechanical constraints.
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 system provides a robust, smooth, and efficient power transmission without limit stops or over-run clutches, improving ergonomics, safety, and efficiency, while allowing for versatile output configurations and orientations, including vertical shafts for watercraft propulsion and horizontal shafts for land vehicles.
Implementation Method 1
spring-tensioned cables, eliminating the need for limit stops and over-run clutches
Data Source
AI summary
A transmission for a human-powered vehicle. The transmission has a primary system that includes a transmission case, a crankshaft with cog, a pair of receiver cranks, a pair of connecting rods, a pair of oscillating driver cranks, and a pair of pedals. A secondary biasing system is engaged with the primary system to provide a favorable torque around dead centers of the primary system. The transmission 150 may be configured to transmit power by driveshaft, chain, or belt to drive a wheel or propeller. In a watercraft application, an operator alternatingly applies force to a pair of pedals while seated close to the floor of a kayak 145. Power from the transmission is transmitted through a steerable lower gear case 134 via a propeller to propel the craft. The operator maneuvers the craft by means of a control lever 135 operably connected to the lower gear case by cables 136.