Re: Microstepping thru the Tulips

The basics:

1) A step motor is a "constant power" motor. This means torque times
RPM gives the same number for any point on the speed-torque curve for
an ideal motor.

2) Winding current is proportional to torque.

3) A near-zero speed would require a near-infinite torque for this to
be true. This would require a near-infinite current.

4) A step motor drive is designed to limit current. This limits
torque as well. The result is a 2-piece speed-torque curve; torque is
constant from zero RPM to the RPM where it interesects the motor's
natural speed-torque curve. Past that point, torque drops as the
inverse of speed. This is the corner speed of the motor.

5) Power output (speed times torque) increases linearly from zero
power at zero RPM until RPM reaches the corner speed. Past that speed
power remains constant. Gear the motor to the corner speed.

6) Doubling the power supply voltage doubles the corner speed. This
doubles the motor power output.

7) Power supply voltage has no effect on low-speed torque or holding
torque. That is set by the current limit setting of the drive.
--------------------

I have some dynamometer curves that illustrate the above points.


Mariss





--- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
<lcdpublishing@...> wrote:

>
> Based on what I am seeing it sure appears as though there is a very
> high potential for having positional problems at these higher step
> rates too then.
>
> Perhaps Maris could shed some light on the relationship between the
> torque/speed curves and the transitional point where chopping

ceases

> to perform completely.
>
> (major snip)