Crankset Power Measurement via Spider Strain Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bicycle power measurement systems, particularly those measuring power at the driven hub, face inaccuracies due to drive line losses and external factors, while crankset measurements can be inaccurate and prone to operational issues, making it challenging to obtain a precise and objective measure of a cyclist's effort.
Innovation Solution
An input torque measuring device for a bicycle's drive train that includes a spider connected to the crank arms, equipped with strain measurement devices and sensors to directly measure the force applied to the chain rings, providing accurate and objective power output calculations by isolating external factors and internal loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If power is measured at the driven hub, then measurement accuracy is improved, but the measurement represents power minus drive line losses and is affected by external factors
Solution Approach 1:
The patent extracts the power measurement point from the driven hub and relocates it to the crankset, specifically at the spider where the chain rings are mounted. This extraction removes the measurement from the affected zone of drive line losses and isolates it to a point where only the cyclist's direct input force is measured, eliminating the harmful factors of chain losses, bearing friction, and flexibility variations.
Solution Approach 2:
The spider serves as an intermediary measurement point between the crank arms and the chain rings. By mounting sensors on the spider, the system creates an intermediate measurement zone that captures the force directly transmitted from the crank arms to the chain rings, acting as a mediator that isolates the measurement from the variable losses in the drive line components.
2Power
If conventional crankset power measurement systems are used, then direct power measurement is achieved, but inherent inaccuracies and operational issues occur
Solution Approach 1:
The patent applies local quality by focusing the measurement at a specific localized point on the spider where the chain rings are mounted. Instead of measuring power at various points along the crank arms or at the bottom bracket, the system concentrates the measurement at this specific location where the force transmission path is most direct and least variable, improving precision by eliminating measurements at locations with inherent operational issues.
3Ease of operation
If measurements are taken at the chain or bottom bracket, then power measurement is possible, but the measurements are indirect and less precise
Solution Approach 1:
The patent segments the power measurement system into distinct measurement zones: the crank arms, the spider, and the chain rings. By placing sensors on the spider, the system creates a dedicated measurement segment that is neither as indirect as bottom bracket measurements nor as variable as chain measurements. This segmentation allows for a precise measurement point that is easily implemented by simply mounting sensors on the existing spider structure.
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 provides a more accurate and objective measurement of a cyclist's power output by directly measuring torque at the crankset, reducing the impact of external and internal factors, thus enhancing the precision and reliability of power measurement.
Implementation Method 1
at least one strain measurement device configured to generate an electronic signal when a force is applied to the crank arm
Implementation Method 2
The spider may include a plurality of sensors configured to respond to the force applied by the spider to the at least one chain ring. The sensors produce an electronic signal relative to the force transmitted by the spider to the at least one chain ring.
Data Source
AI summary
The present application relates to an input torque measuring device for a drive train of a bicycle. The drive train includes a first crank arm and a second crank arm. An inboard end of each crank arm is rotatably mounted to the bicycle at a bottom bracket of the bicycle. At least one chain ring is configured to rotate a driven wheel of the bicycle. A spider is connected to the first crank arm adjacent the bottom bracket and extends out to the at least one chain ring. The chain ring is attached to the spider by a fastener extending through a bushing within an opening of the spider. Sensors may be attached to the spider or the crank arms and may be directly connected to a flexible circuit board. The sensors, the flexible circuit boards and other components of the input torque measuring device may be encapsulated in a protective material.