Lesson 14 Control the Step Motor

Introduction of step motor

The step motor we use here have 4 coils. The motor rotates 4 degrees if one coil is powered. If we want the step motor rotate another 4 degrees, we should power another coil.

We should power these 4 coils in proper sequential order so that the step motor may rotate continually.

If we power these 4 coils in a contrary order, then the step motor will rotate reversely.

Try to power these 4 coils and find out the proper sequence of 4 coils.

Here we will use a simple circuit to make the step motor rotate. There are many kind of IC in market which is specially designed to drive step motor.

It is easy to control step motor speed and rotate angle precisely.

It is difficult to control speed and rotate angle of DC and AC motor.

So in most case we add a sensor to the DC or AC motor to sense the condition of rotate and feedback to the control circuit. That is called servomotor.

Servomotor use close loop control. Step motor use open loop control.

Step motor is widely used in disk driver, scanner, printer, automatic machine…

There are a variety of step motor in market, some has 4 coils, some has 2 coils.

Step motor

Experiment 1 Turn on 4 LEDs sequentially

We use a 4017 IC to distribute the output of 555 to 4 LEDs.

Try different R1 and C, and see what happens to these 4 LEDs.

Experiment 2 Let the step motor rotate

1 Try and find out the meaning of 5 wires of the step motor. at first.

2 Try different R1 and R2, observe the change of speed.

3 Let the step motor rotate reversely.

4 replace R2 with a potentiometer. Vary the step motor speed by potentiometer.