Moment of interia of an armature 2

[bernardg]

Hello All,

We make 3.0" DC motors... and for some blower applications, we mount the wheels to the shaft and assemble the motor-wheel into blower housings.
Because of the tight clearance that we maintain between the wheel and the housing... even when the motor shaft flexes a little due to the armature imbalance, the wheels start to hit the housing and damages it.

Our customer wanted us to find the moment of interia of the armature. (Not the moment of interia of the armature while it is running in the motor... but just the armature as is). How would I do that?

Your input would very much be appreciated.

Thanks,
Bernie

 

[Skogsgurra]

A good stroboscope will reveal what happens. It is fascinating to actually see what is going on in a fan wheel with vibrations. If you have resonances, you will quickly shut down the fan because what you see will make you afraid. Seen that.

 

[sreid]

Although the general feeling is that the failure has nothing to do with the motor's moment of inertia a rough estimate for the moment of inertia is to assume the rotor is a solid steel cylinder. The coper in the slots is more dense than steel but the slots are not 100% filled. The formula is

I = (0.0041)(R^4)(L)(p)

where

I = Moment of Inertia oz-in-sec^2

R = Cylinder Radius inches

L= Cylinder Length inches

p = Density of Steel 4.5 oz/in^3

 

[itsmoked]

Yeah skogs! An wear a kevlar face shield!!