Re: [CAD_CAM_EDM_DRO] Re: re-selection of motors....avoiding another rathole - question ?

turbulatordude wrote:

>Reading this thread, I am to understand that the mini-mill is run
>with servos from Geckos.
>
>that the motor(s) may be undersized.
>
>My question then is would an undersized motor be under higher power
>to reamain on posisition (per encoder feedback) than a larger motor ?
>
>or maybe stated differently, would a smaller motor get hotter than a
>larger motor when used in this way ?
>
>

It certainly will when moving. Depending on the dithering characteristics
of the servo control, and whether there are any biases or stiction that keep
it applying force in one direction all the time, then it could also get
quite
hot just when idling. If it has to resist tool cutting forces, for
instance, then
it would also work harder, and get hotter.

>It may be as simple as calculating the ammount of work needed to hold
>posistion as a figure of watts. if that is the case, then a larger
>motor operating with the same wattt load would be cooler to the touch.
>
>

This is not so easy, since when holding, the mechanical output of the motor
is zero. But, you find the current needed to produce the holding
torque, and
then you can calculate the heating as I^2 * R.

Jon