Re: [CAD_CAM_EDM_DRO] Re: What makes a motor a servo?

cnc_4_me wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
>
>>as soon as it lags more than 180 degrees (2 full steps) the torque
>>violently reverses,
>>and the motor slams to a stop
>>
>>
>
>
>This is something i have been wondering about for a long time. Are
>the 2 steps you talk about gosple or is that a educated guess.
>
>

No, it is almost perfect gospel. The pattern of currents in a stepper motor
repeats every 4 full steps. So, if the motor gets exactly 180 degrees
behind
the steps (that equals 2 full steps) then it has equal forces pulling in
both
directions. Depending on the torques on the shaft at that exact moment, it
will choose to go one way or the other. Think of it as a bunch of
sinusoidal
ocean waves, and a ball floating on the waves. The ball will naturally
settle
in the trough between waves. If you pulled sideways on the ball with a
rope,
it would ride up the side of the wave and exert an opposing force. If you
got the ball exactly on the top of the wave, it could slide down either way.
(I hope this analogy makes sense.)

Jon