Moment of Inertia vs Weight (which is important?)

[BMV_Deutsch]

I'm just wondering if anyone can shed some light on this as I am a COMPLETE NOOB. When it comes to designing a set of Drivetrain components, what should we be paying more attention to:

Moment of Inertia or the weight of the components?

We are in the middle of finalising our design and 2 options have presented themselves.

Option 1 - where the total weight of its components are about 100-200grams (about 600grams )lighter but its total Moment of Inertia is about 3.55e-03kg m^2

Option 2 - Weight is about 700-800grams. its total Moment of Inertia is 3.03e-03 kg m^2

If anyone could share their thoughts on this, it would be greatly appreaciated http://fsae.com/groupee_common/emoticons/icon_smile.gif

[nowhere fast]

You can convert rotational inertia into an equivalent translational inertia by writing out the equations for kinetic energy of the components at a given car speed, noting the relationship between the rotational velocity of the component and the velocity of the car.

I used this technique to compare designs when working on hubs and wheel centres.

[thewoundedsoldier]

What are the goals of the car? I can see your choice being guided by what general type of car you want to design and how you want it to behave.

A vehicle simulation model/tracksim/points optimization would help. This would help you quantify the importance of both reduced vehicle weight and driveline response.

It's weird that you would know the mass moment of inertia with such precision but have only 100g resolution when it comes to mass. If it were up to me (which it never is), I would save the mass.

[Demon Of Speed]

Remember to thing about unsprung vs sprung weight as well.

[BMV_Deutsch]

Thanks for the sugguestion guys http://fsae.com/groupee_common/emoticons/icon_smile.gif

No i mean from an Engineering point of view. Would it be ideal to increase about 17% of Inertia moment to reduce about 15% of mass. I think my problem here is that I have trouble identifying the magnitude of both quantities.

[SNasello]

Make an estimate of the mass moment of inertia of the wheels, tires and hubs. Include the final drivetrain inertias and calculate what the difference between the two concepts is in terms of a percentage. It may then become quite clear which is more significant.

[Gruntguru]

After converting MOI to equivalent mass, consider also that component mass affects cornering and aceleration/braking and normal force at the contact patch. MOI only affects acceleration/braking. (Hint. Cornering ability is much more significant in terms of lap-times/competition-points thatn acceleration and braking.)