moment of inertia units in Solidworks?

[mrPelagic]

Does anyone know the units that solidworks is using to compute moment of inertia? I am trying to size a stepper motor, and am a bit confused.

It's been a while, but it looks like it's (pounds force * in^2)

I=.5mr^2 (for a cylinder) which translates to (kg*m^2) or (lbm*in^2) or [(lbf/32.2) * in^2]. This gets into that whole slugs thing- which I admit coufounds me.

For instance, given a 2 inch diameter cylinder weighing 1 pound, solidworks gives me 0.5 lb*in^2, while I get 0.5/32.2 lbm*in^2.

Now, torque= I*alpha.
to size a motor, I need the proper acceleration torque. to me, if I use solidworks' Ixx, I will be 32 times stronger than I need to be to accelerate my carousel.

anyone agree?

 

[handleman]

2 letters: S I.

 

[meintsi]

Moments of Inertia deals with the mass, not force.

As as far as the 'slug' conversion, you are forgetting the proportionality constant g_c.

In the English Engineering system of units the primary dimensions are are force, mass, length, time, and temperature. The units for force and mass are defined independently:

1) The basic unit of mass is pound mass (lbm)
2) The unit of force is the pound (lb) alternatively pound force (lbf).

In the EE system 1 lb of force will give a mass of 1 lbm a standard acceleration of 32.174 ft/s².

Newton's Second Law can the be modified to:

F = ma/g_c

Converting to weight we get:

w = mg/g_c


Remember...
[navy]"If you don't use your head,[/navy]
[navy]your going to have to use your feet."[/navy]

 

[Heckler]

Give us a little bit more information on your design. What load are you trying to move? Is there any gear reduction between load and motor? You will need to calculate the reflected load inertia these steps can be obtained from any motion control expert. What are the motor specs max rpm, motor torque, & torque curve

Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 5.0 & Pro/E 2001
Dell Precision 370
P4 3.6 GHz, 1GB RAM
XP Pro SP2.0
NVIDIA Quadro FX 1400
o
_`\(,_
(_)/ (_)

Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.

 

[Heckler]

One more thing. I would convert to the metric system....

Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 5.0 & Pro/E 2001
Dell Precision 370
P4 3.6 GHz, 1GB RAM
XP Pro SP2.0
NVIDIA Quadro FX 1400
o
_`\(,_
(_)/ (_)

Never argue with an idiot. They'll bring you down to their level and beat you with experience every time.