Re: [CAD_CAM_EDM_DRO] Re:Stepper Motor vs Servo Motor

John wrote:

> > They have full torque at 0 speed but tend to drop as speed increases.
> > Modern drivers have made these motors perform quite well. They are
> > easy to drive and maintain and are open loop capable. All the
> > positioning is done by the motor design you just tell it how many
> > steps to take by driving the coil sequence.
>
> An excellent post! I haven't taken the time to read through and fully
> understand how steppers function in all the different modes yet but I have a
> rough idea. I don't know how the actually stepper itself moves though.

There are magnets in the rotor, and metal plates with many teeth. For a
200 full-step per rev motor, there will be 50 teeth on the rotors, and 50
teeth (poles) on the stator. There are 2 sets of magnets and 2 sets of
stator poles, and they are arranged 90 degrees out of phase, thereby
setting the quadrature relationship between the two phases of the motor.

> You
> say they have less torque at full speed, I know that, but why do they have
> any at all?

Why do they have any torque? Because electrically-produced magnetic
stator fields from the coil windings produce forces when they interact
with the fields from the permanent magnets.

> Isn't there ever a point where there is no power to any of the
> coils, or does the control fade between them?

Since there are 2 sets of coils, there is always power in one of them.
Different phase schemes may have only one coil on at a time, or have
both on some of the time, and only one on at some times, but generally
there is some current in at least one winding at all times.

> Do the coils active and pull
> the magnets towards them or push them away?

Both. The arrangement is such that there is always an N and an S rotor
pole near each stator pole. Depending on which way the current flows in
the coil, it pulls one and pushes the other. When you reverse the current,
which one gets pulled or pushed switch.

Jon