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Shape suggestions for known mass & inertia


Hi all,

I am trying to develop a revolved shape that will have a known mass = 130 kg and known I (about the rotation axis) = 3.6e7 kg*mm^2 and must fit inside the cylinder with Do <= ~1200 mm, Di >= ~300 mm and Length < 450 mm.

Shape is completely arbitrary and density can be modified as well. I tried many obvious shapes and can not get the inertia high enough with the variables I have. Any suggestions? I am using Pro/ENGINEER's Behavioral Modeling functionality.

Thanks in advance.

Best regards,

Matthew Ian Loew


Start with a solid and just remove material at the neutral axis until you meet your goal... Then adjust the density to meet your mass goal.

If a solid won't give you enough 'I', ... punt.


Luis Aguirre

New member
Hello Mattew,

If you have BMX, this problems sounds as good candidate. Although, How can you change the density of the material you are going to use ? I will try to run the problem on Monday and if I get a solution will send it to you.



Thanks for all the information and encouragement.

In a thread on another forum I posted this on, it was pointed out there are some discrepancies on the equations for closed form solutions. Interesting, my second edition of Fundamentals of Machine Component Design by Robert C. Juvinall & Kurt M. Marshek ( has the equation with the