Vehicle Moment of Inertia? How?

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Discussion Overview

The discussion revolves around the methods for experimentally determining the moments of inertia of vehicles, which are essential for vehicle dynamics simulations. Participants explore various approaches and tools that could be utilized to estimate these inertial properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about experimental methods to calculate vehicle moments of inertia, expressing a desire for conceptual ideas beyond traditional methods like pendulums or rotating tables.
  • Another participant suggests checking Wikipedia for definitions and references related to inertia and moments of inertia, indicating that standard formulas for spring-damper systems might be relevant.
  • A participant emphasizes the need for specific inputs required for vehicle dynamics models and mentions the importance of accurately modeling the system rather than using simplified assumptions.
  • Several participants propose breaking down the vehicle into components to estimate mass and center of gravity (CG) for each piece, with one noting that the engine's inertia properties could be approximated as a uniform block of material.
  • There is mention of using the parallel axis theorem to calculate total inertia from component parts, with one participant indicating that this is a common practice during the design stage.
  • Another participant suggests that car scales could be utilized to find various moments experimentally, although this idea is not elaborated upon in detail.

Areas of Agreement / Disagreement

Participants express various methods and ideas for estimating moments of inertia, but there is no consensus on a single effective experimental approach. Multiple competing views and suggestions remain present throughout the discussion.

Contextual Notes

Some participants mention limitations in available data and the challenges of obtaining real properties for all vehicles, indicating that existing databases may not cover all models. There is also a recognition that experimental methods may vary in accuracy and feasibility.

Who May Find This Useful

This discussion may be of interest to engineers, vehicle dynamics researchers, and hobbyists involved in vehicle simulation and design, particularly those seeking experimental methods for calculating inertial properties.

jprecinos
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I have been playing with several vehicle dynamics simulators for a while now, and many of them require vehicle inertial properties to create realistic simulations.
There is very limited published data out there so I was wondering how could one calculate these properties experimentally? ...Other than hanging it on a huge pendulum or creating a big rotating table is there an easy way to estimate the principal moments of inertia of an actual size vehicle?
Any conceptual ideas would be helpful. Thanks JP
 
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It would help if you specified just what inputs are required for your models.

Try checking wikipedia for INERTIA and MOMWNT OF INERTIA as a start.

See the reference at the bottom of each article like this one:

http://en.wikipedia.org/wiki/List_of_moments_of_inertia



Also, seems like an auto is very much like a spring a damper system (coil springs,struts,etc).

so check out the standard formulas for such system dynamics.
 
I also found this in wikipedia:

http://en.wikipedia.org/wiki/Swept_path_analysis

hope this helps...
 
Inertial paramaters of a dynamic object:
1. CG location - easy to get. no problem
2. Moments of inertia: Yaw, Pitch, Roll
how to calculate the moments experimentally?

Yes, most simulators model vehicle dynamics as a spring, damper system, some use a more complexe model than others (with more DOF). Inertia parameters however are always needed and that is more of a geometrical and mass distribution problem. It wouldn't be accurate to model the system with the Moments of Inertia of a box for example...the dilema is how to get the Ixx, Iyy and Izz for a vehicle.
 
I have been playing with several vehicle dynamics simulators for a while now, and many of them require vehicle inertial properties to create realistic simulations.


Well if people have developed vehicle simulators, I would hope there were input parameters to make them useful.

All I can suggest is google type searching...or post your issue in an engineering forum if nothing further turns up here.
 
Make a model of the vehicle split into pieces where you can estimate the mass and CG position of each piece. Probably the most massive single "piece" would be the engine, which will have pretty much the same inertia properties as a block of material with uniform density.

You will have to "tweak" the complete model to get its total mass and CG in the correct position. Then work out the inertia from the components, using the parallel axis theorem etc.

That's the way it is done in "real life" at the design stage, though obviously it is easier if you are starting from a detailed CAD of the complete vehicle.
 
Naty1 said:
Well if people have developed vehicle simulators, I would hope there were input parameters to make them useful.

All I can suggest is google type searching...or post your issue in an engineering forum if nothing further turns up here.

Well the purpose of most simulators is to give you a plattform to recreate dynamics of a variety of vehicles during different scenarios. They do have some starting imput parameters but they won't have real properties on all vehicles out there. I do have access to some engineering databases and the National Higway safety has published some numbers but not on all vehicles either. I will keep on searching :)
 
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AlephZero said:
Make a model of the vehicle split into pieces where you can estimate the mass and CG position of each piece. Probably the most massive single "piece" would be the engine, which will have pretty much the same inertia properties as a block of material with uniform density.

You will have to "tweak" the complete model to get its total mass and CG in the correct position. Then work out the inertia from the components, using the parallel axis theorem etc.

That's the way it is done in "real life" at the design stage, though obviously it is easier if you are starting from a detailed CAD of the complete vehicle.

yes CAD and FEA is my plan B. But I was hoping that there would be an experimental way to find a solution ... Like those little intertia apparatus they have at the physics labs. An experiment along those lines I was hoping :)
 

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Seems to me that a set of car scales could be used to find the various moments experimentally.
 

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