NC Cams,

Good points; let's look at them:

1) A 10-microstep drive on a 1.8-degree motor takes 2,000 steps for one revolution. At low speeds, each step is a 0.18-degree increment of motion (move, stop, move again).

2) A servomotor equipped with a 500-line encoder also takes 2,000 steps for one revolution. At low speeds the motion is also incremental (0.18-degrees) because the encoder is incremental. It also has a move, stop, move again motion.

There is no difference between the two.

Servos can have a continuous following error if the feedback is PD and a transient following error if the feedback is PID.

Steppers always have a no-load following error of -1.8 degrees at moderate to high speeds because of inductive current phase lag (-90 electrical degrees). Add to this a zero to -1.8 degrees of load dependent following error and a stepper can be up to -3.6 degrees out of position at higher speeds. This is equivalent to -20 encoder count following error for a 500-line encoder.

Step motors aren't really step motors. They are high pole-count (50-poles for a 1.8 degree motor) AC synchronous motors.

Mariss