topic Re: Finding Torque Requirement of a Spinning Assembly (Iyy?) in Inventor Forum

Finding Torque Requirement of a Spinning Assembly (Iyy?)

Anonymous — Wed, 09 Oct 2019 15:38:16 GMT

Hello Inventor Wizards,

I have a turntable design and I want to turn it from center shaft with a sprocket, kind of like a bicycle. The trouble is, I don't know what value to put for "I" in T = I * (alpha) so I can get a required torque. I suspect it's Iyy because the turntable will rotate about the Y-axis. Is that correct?

I have a handle on all the other aspects of angular acceleration, gear ratios and all that. Only my figures aren't adding up and I chased all the error out of everything but Iyy.

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

Frederick_Law — Wed, 09 Oct 2019 16:02:42 GMT

Enough torque to over come friction.

After that its how fast you want to accelerate.

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

Anonymous — Wed, 09 Oct 2019 18:00:27 GMT

I don't know what value to put for "I" in T = I * (alpha) so I can get a required torque. I suspect it's Iyy because the turntable will rotate about the Y-axis. Is that correct?

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

swalton — Wed, 09 Oct 2019 18:43:57 GMT

I typically go to Oriental Motor's website for initial sizing calculations.

https://www.orientalmotor.com/motor-sizing/rotaryDevice-sizing.html#

Which Iyy are you using?

Mass Moment of Inertia?

https://en.wikipedia.org/wiki/Moment_of_inertia

Or the Area Moment of Inertia?

https://en.wikipedia.org/wiki/Second_moment_of_area

Do a hand calculation of a shape similar to your actual turntable. Which of the various Mass Moment of Inertia values are close to the one you calculated?

You can also use Dynamic Simulation to study the torque required in your machine.

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

Frederick_Law — Wed, 09 Oct 2019 18:45:54 GMT

"I" here is Angular Momentum.

Assuming your turn table is round:

http://www.softschools.com/formulas/physics/torque_formula/59/

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

Anonymous — Wed, 09 Oct 2019 20:54:38 GMT

Thank you for the helpful links.

I am using the Global Iyy in the Physical tab of the iProperties dialog box. These values are mass moments of inertia. The rotating components of the turntable are in an assembly where the shaft is concentric with the Y-axis.

The second moment of inertia unfortunately is not useful in my application.

The geometry of what is on the turntable is complex. I have performed hand calculations on a cylinder to attempt to prove which value is what I am looking for. Iyy was the closest with reasonable confidence. Even so there is some discussion among my colleagues as to witch I-value is correct.

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

Anonymous — Wed, 09 Oct 2019 20:57:46 GMT

Thank you for attempting to answer my question. I actually have all of this well in hand, except which I-value to use from the Physical tab in the iProperties dialog box, where an object is rotating about the Y-axis.

Re: Finding Torque Requirement of a Spinning Assembly (Iyy?)

Frederick_Law — Wed, 09 Oct 2019 21:11:10 GMT

Draw a circular disc. Same orientation as turn table. Compare Iyy to your calculation. It should be the same.

If it is, you can use Iyy on turn table.