Re: re:Servo vs. Stepper Top 10 Lists

Hi,

In the interests of brevity the comments applied to 200 ordinal step
motors. You are correct regarding the other motors.

The 1:2000 does not refer to any paricular microstep resolution,
rather it refers to the +/-5% non-accumulative accuracy of a 200 step
motor. This results in a 0.18 degree error band, 2000 of which fit in
360 degrees. It just happens that a 10 ustep resolution matches a 5%
motor's accuracy.

A couple of things conspire to limit motor accuracy. The first is the
afore-mentioned 5% error. Even if the motor were perfectly accurate,
any applied torque would degrade accuracy.

For simplicity's sake assume there is a linear relationship between
applied torque and motor error. A 100 oz-in holding torque motor
develops that torque only when its shaft has been displaced 1.8
degrees, thus a 0.18 degrees displacement would require only 10 oz-in
of torque.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, ballendo@y... wrote:
> Mariss,
>
> Thank you for the input.
>
> From your top tens:
> >Top Ten Stepper Disadvantages:
> >3) Low accuracy. 1:200 at full load, 1:2000 at light loads.
>
> This would be for a 200 step/revolution motor. Nyden in San Jose
> sells .9 degree size 34 motors. (400 steps/rev) So it would be
1:400.
>
> Others sell steppers with .9 also (usually size 23). Also 1:400.
>
> The cheap "pancake" style motors are usually 15 degrees/step. So it
> would be 1:24.
>
> The 1:2000 is a divide by 10 microstepper, right? Showing what Jon
E
> alluded to. That the microsteps ARE affected by the load, but that
> the full steps will still be the limit, if the motor is properly
> sized for the load?
>
> Ballendo