Can I Accurately Measure Bike Wheel Radius with a Rotating Sensor?

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Discussion Overview

The discussion revolves around the challenge of accurately measuring the radius of a bicycle wheel using a rotating sensor that measures acceleration. Participants explore the complexities of integrating acceleration data to trace the wheel's circular path while accounting for centripetal acceleration and the sensor's dual-axis movement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant describes the intention to trace the displacement of a sensor attached to a bicycle wheel to determine the radius by integrating acceleration data.
  • Another participant points out that the sensor will consistently measure centripetal acceleration directed towards the center of the bike, which complicates the data interpretation.
  • A participant suggests that if the bike's speed can be considered constant, centripetal acceleration can be subtracted from the measurements to isolate tangential acceleration.
  • Concerns are raised about how to achieve an overall displacement measurement given that the sensor's axes are rotating with the bike wheel.
  • One participant outlines a potential approach involving the removal of centripetal acceleration, calculating the angle traveled based on frequency, and converting between the sensor's axes and an inertial reference frame.
  • Another participant asserts that knowing the rotation frequency and wheel radius allows for the calculation of velocity, which can then be integrated to find displacement and verify centripetal acceleration values.

Areas of Agreement / Disagreement

Participants express various viewpoints on how to handle the complexities of measuring displacement with a rotating sensor. There is no consensus on the best approach, and multiple competing ideas are presented.

Contextual Notes

Participants acknowledge the need for assumptions regarding the bike's speed and the effects of centripetal acceleration, but these assumptions remain unresolved within the discussion.

Maria Redericki
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I have attached a sensor measuring acceleration to a bicycle wheel. I was hoping to be able to trace out the circle with accurate measurements for the radius of the bike wheel by integrating my data however I have realized that my sensor is of course undergoing centripetal acceleration however as the x and y-axis of the sensor is rotating with the device ( it's a dual axis device) then thre is a problem is I simply plot x measurements against y measurement. Is there a way around this?
 
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What do you want to measure? A way around what?

Your sensor will always see centripetal acceleration going in the same direction - let's call that direction "x" (towards the center of the bike). For typical velocities of a bike, this will be by far the largest contribution to the measured accelerations. Smaller contributions come from gravity and accelerations of the bike.
 
Well I would like to trace out the displacement of sensor and so get a circle by intergrating acceleration twice. But As you say I have rotational acceleration etc is there anyway I can convert this to linear displacement so that I trace out the wheel circle of radius 30 cm? I am using a dual axis device
 
If you can neglect a change in the speed of the bike, centripetal acceleration should be constant and can be subtracted.
Otherwise, you'll have to add some assumptions about your motion I think.
 
Well I know that it would be subtracted out to then give tangential acceleration, however as the axis are moving with sensor on wheel of bike I am a bit confused how I can get an overall displacement. I am thinking that because these axis move with sensor how can I trace out an overall circle?
 
To be honest I think i have an idea but I am not sure if there is something I am not considering... This is my steps of my approach that I am thinking to take
a. remove centripedal acceleration
b. Using my frequency (it at some point 3 Hz) of bike turn I am able to work out how much angle it has traveled at any given time.
c. I know that axis travels with object so to the convert to overall axis I convert between my axis and inertial axis
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is this correct approach.
 
If you know the rotation frequency and the radius of the wheel, you are done - this gives you the velocity and integrating over that gives the displacement.
Based on the velocity you get, you can also check if the centripet[/color]al acceleration matches the expected value.
 

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