How do I calculate moment of inertia in a wheel?

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Discussion Overview

The discussion centers around calculating the moment of inertia (MOI) for a system of two wheels connected by an axle, with a focus on theoretical approaches rather than experimental methods. Participants explore different ways to model the system to find the torque based on given parameters such as weight, distance between wheels, and angular acceleration.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant describes the system parameters, including weight, distance between wheels, and tire diameter, and seeks guidance on calculating the moment of inertia to find torque.
  • Another participant suggests using Finite Element Analysis (FEA) modeling or physical testing to determine the moment of inertia, questioning the availability of testing equipment.
  • A participant indicates they do not have access to testing equipment and assumes a perfect system, focusing on theoretical calculations.
  • One participant inquires about the experience level with MOI calculations and proposes approximating the MOI by modeling the system with component pieces.
  • A participant with limited experience mentions they are working on this as a final project and have been advised by their supervisor to keep the project simple.
  • Another participant suggests modeling the axle as a shaft and the wheels and tires as disks, indicating that the MOIs can be added linearly based on component densities.
  • A participant expresses appreciation for the modeling approach and acknowledges it will aid in their project, despite not being able to implement it immediately.
  • One participant asks for clarification on which moment of inertia is desired and the reference axis for the calculation.

Areas of Agreement / Disagreement

Participants generally agree on the approach of modeling the system with component pieces to calculate the moment of inertia, but there is no consensus on the specific methods or calculations to be used, as some participants suggest different modeling techniques and testing methods.

Contextual Notes

Participants express varying levels of experience with moment of inertia calculations, and there are references to assumptions about the system being ideal. The discussion includes suggestions for modeling approaches that depend on the densities of materials used, which may not be fully resolved.

Who May Find This Useful

This discussion may be useful for students or individuals working on projects involving rotational dynamics, particularly those interested in calculating moment of inertia for mechanical systems. It may also benefit those seeking to understand different modeling approaches in theoretical physics or engineering contexts.

shannonxtreme
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What I have are two wheels, weight assumed at 50 kg overall for both, joined by an axle. The wheels are 900 mm apart from the centre of one tire to the centre of the other. The diameter of the tire is 690 mm. How do I calculate the moment of inertia in order to find the torque in the centre of the axle?

For the torque calculation I know the angular acceleration is -0.43rads^-2
 
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shannonxtreme said:
What I have are two wheels, weight assumed at 50 kg overall for both, joined by an axle. The wheels are 900 mm apart from the centre of one tire to the centre of the other. The diameter of the tire is 690 mm. How do I calculate the moment of inertia in order to find the torque in the centre of the axle?

For the torque calculation I know the angular acceleration is -0.43rads^-2

For a real system like that, you would either use FEA modeling or do a physical test. Do you have access to a dyno?

EDIT -- Or do you have access to the physical system? You can use a falling weight on a rope to calculate the moment of inertia MOI with an experiment...
 
berkeman said:
For a real system like that, you would either use FEA modeling or do a physical test. Do you have access to a dyno?
Nope, I do not have access to any testing equipment right now. I'm assuming its a perfect system, just need the theory right now. Testing and implementation when I have access to materials :)
 
How much experience do you have with MOI calculations? You can approximate the MOI with several component pieces...
 
Little to no experience other than basic theory. I'm doing this as my final project for my bachelors, and my project supervisor says I don't need to make it over complex because I just don't have the experience
 
shannonxtreme said:
Little to no experience other than basic theory. I'm doing this as my final project for my bachelors, and my project supervisor says I don't need to make it over complex because I just don't have the experience

So model the system with a series of disks and shafts, and add up the MOIs of the components. They add linearly.

So model the axle as a shaft, the wheels as disks, and the tires as a combination of disks and the outer bands. Each component will have the appropriate density (steel or rubber). Does that seem do-able?
 
berkeman said:
So model the system with a series of disks and shafts, and add up the MOIs of the components. They add linearly.

So model the axle as a shaft, the wheels as disks, and the tires as a combination of disks and the outer bands. Each component will have the appropriate density (steel or rubber). Does that seem do-able?
That actually does! Thanks a million! I won't be able to do that for my interim report tomorrow but this will help a great deal :)
 
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What MMOI do you want to find? What is your reference axis?
 

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