Re: [CAD_CAM_EDM_DRO] Rotor inertia.

Jason Cox wrote:

>Hello All,
>
>Just wondering when selecting servo motors what impact does rotor inertia have on the final function of a cnc machine?
>
>>From my research motors with a far lower inertia are much cheaper, but does this really matter. Surely the redution in inertia of the rotor would be minimal say compared to the inertia of the machine table.
>
>

Yes, essentially correct. Mariss Freimanis did some calculations that I
seem to
recall showed that it is not insignificant, but that common motors come
out in
the right range. Under some circumstances, a motor with too much, or too
little inertia can make for an unstable servo system. This is especially a
problem when there is some springy element between the motor and the
high-inertia load, such as a long thin leadscrew or couplings with too much
flex. You end up with a system comparable to two masses connected by a
spring.

Are you sure low-inertia motors are cheaper? I happen to have some low
inertia Yaskawa super minertia motors that supposedly cost $5000 each.
They were in computer tape drives, and had a fiber composite capstan
with Beryllium hub, a ceramic shaft, ironless rotor motor of the "thimble"
style, etc. But, in general, a low inertia motor of conventional
construction
is just smaller, that's all. So, a smaller motor qould be cheaper to make.

Jon