Stepper Motors Basics
There are two basic types of stepper motors in common use:

permanentmagnet
variable reluctance


Permanent magnet motors are divided into bipolar andunipolar types.
Bipolar Motors

Simplified to the bare essentials, a bipolar permanent magnet motorconsists of a rotating permanent magnet surrounded by stator poles carrying windings.Bidirectional drive current is used and the motor is stepped by switching the windings insequence.

For a motor of this type there are three possible drive sequences.

The first is to energize the windings in the sequence AB/CD/BA/DC (BAmeans that the winding AB is energized but in the opposite sense). This sequence is knownas "one phase on" full step or wave drive mode. Only one phase is energized atany given moment.

The second possibility is to energize both phases together, so that therotor always aligns itself between two pole positions. Called "two-phase-on"full step, this mode is the normal drive sequence for a bipolar motor and gives thehighest torque.

The third option is to energize one phase, then two, then one, etc., so that the motor moves in half step increments. This sequence, known as half step mode, halves the effective step angle of the motor but gives a less regular torque. This is the default method that the XYYZ and XYYZBboards produce.

For rotation in the opposite direction (counter-clockwise) the samethree sequences are used, except that the order is reversed.

As shown in the diagram the motor would have a step angle of 90. Real stepper motors have multiple poles to reduce the step angle to a few degrees but the number of windings and the drive sequences are unchanged.   Most stepper motors have a full step angle of 1.8 degrees, half step angle of 0.9 degrees.

Unipolar Motors

A unipolar permanent magnet motor is identical to the bipolar motordescribed above except that bifilar windings are used to reverse the stator flux, ratherthan bidirectional drive.

This motor is driven in exactly the same way as a bipolar motor exceptthat the bridge drivers are replaced by simple unipolar stages - four darlingtons or aquad darlington array can be used. Unipolar motors have twice as many windings. Unipolarmotors give less torque for a given motor size because the windings are made with thinnerwire. Unipolar motors are attractive to designers because they simplified the driverstage.

All permanent magnet motors suffer from the counter EMF generated bythe rotor, which limits the rotation speed. When very high slew speeds are necessary, avariable reluctance motor is used.  Experience has shown that 3-4 revolutions persecond is possible with simple conventional driver circuits.

Variable Reluctance Motors

A variable reluctance motor has a non-magnetized soft iron rotor with fewer poles than the stator. Unipolar drive is used and the motor is stepped by energizing stator pole pairs to align the rotor with the pole pieces of the energized winding.

Once again three different phase sequences can be used. The wave sequence is A/C/B/D; two-phase-on is AC/CB/BD/DA and the half step sequence is A/AC/C/BC/B/BD/D/DA.

Stepper motors normally employ multiple poles to give a much smaller step angle than the illustrations. The step angle of 1.8/.9 Full/Half step mode are mostcommon. The principle of operation or the drive sequences remains the same.

Super Tech Motor Connector Configuration

The schematic is how we wire the stepper motor connectors. By hooking the motors up this way, a unipolar motor can be run on a bipolar controller. Should a bipolar motor get hooked to a unipolar controller, there would be no damage to either.

Pictures of Mechanical drawings for NEMA 23 and 34 Stepper Motors

drawings for NEMA 23

drawings for NEMA 23

drawings for NEMA 23

drawings for NEMA 23

drawings for NEMA 23

drawings for NEMA 23

drawings for NEMA 34

drawings for NEMA 34

drawings for NEMA 34
Stepper Motors used for CNC control Picture Gallery

Double Stack NEMA 23 Stepper Motor with 0.25 inch diameter shaft, 0.81 inch long.

NEMA 34 Single Stack Stepper motor with 0.500 inch Shaft with Key

Double Stack NEMA 34 Stepper Motor with 0.500 inch Shaft with Key

Double Stack NEMA 23 Stepper Motor with 0.25 inch diameter shaft, 0.81 inch long.

NEMA 34 Single Stack Stepper motor with 0.500 inch Shaft with Key

Double Stack NEMA 34 Stepper Motor with 0.500 inch Shaft with Key

Single Stack NEMA 23 Stepper Motor with 0.25 inch diameter shaft, 0.81 inch long.

NEMA 23 Stepper Motors

NEMA 23 Stepper Motor looking at the end that mounts to the mechanisms

This is the Male DB9 connector used to connect to the motors supplied by Super Tech.

Limit Switch that is connected to pins 8 and 9 on the DB9 Male connnector. This switch is to be used as the home sense switch.

Limit Switch that is connected to pins 8 and 9 on the DB9 Male connnector. This switch is to be used as the home sense switch.
Motor Prices


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Copyright 2016 Dennis Bohlke
Revised 03/12/16