Stegmotor

Additional description

Stepper motors are used when a motor needs to rotate in precisely defined steps and be controlled with high accuracy. They are available in different sizes, designs and electrical configurations and can be used in CNC machines, 3D printers, robotics, automation and various electronics projects.

Motor length and strength
For stepper motors, particularly NEMA motors, motor length is often a good indication of the motor's potential torque. A longer motor usually has a greater active magnetic length and can therefore provide higher holding torque and running torque. For example, a 40 mm long NEMA 17 motor is normally stronger than an otherwise equivalent 30 mm long NEMA 17. Motor length is not, however, an exact measure of motor strength. When comparing motors, the holding torque, specified in Ncm or Nm, should be the primary value to consider.

Voltage supplied to the stepper motor driver
The supply voltage specified for the stepper motor driver is not the same as the motor's rated voltage. A stepper motor is normally controlled by a current-regulated driver. The driver can, for example, be supplied with 12 V or 24 V while regulating the current through the motor windings to the correct level. A higher driver supply voltage can provide better performance at higher speeds because the current can build up faster in the motor windings. Therefore, 24 V can often be advantageous compared with 12 V when higher speed and better torque at higher speeds are required. Always check that the selected driver supports the intended supply voltage.

Rated current
Rated current is one of the most important specifications when selecting and using a stepper motor. It indicates the current that should normally be allowed to flow through each motor winding. For example, a rated current of 1.5 A normally means that the stepper motor driver should be set to approximately 1.5 A per phase, according to the motor and driver specifications. Excessive current can cause the motor to become very hot and may damage the windings, while insufficient current results in lower torque.

Rated voltage
Rated voltage is the approximate voltage across the motor winding and can be calculated from the rated current and winding resistance:

Rated voltage = rated current × winding resistance

For example, if a winding has a resistance of 1.7 Ω and the rated current is 1.9 A, the resistive voltage is approximately 3.2 V. This does not mean that the motor should be connected directly to a 3.2 V power supply. A stepper motor should normally be connected to a suitable current-regulated stepper motor driver.

Rated voltage and driver supply voltage are therefore two different things. A motor can, for example, have a rated voltage of approximately 3 V while being operated with a driver supplied with 12 V or 24 V. The driver regulates the current so that the motor's rated current is not exceeded.

Step angle and number of steps
The step angle indicates how far the shaft rotates for each full step. A common stepper motor with a 1.8° step angle has 200 full steps per revolution. With microstepping, the driver can divide each step into several smaller steps, such as 1/2, 1/4, 1/8 or 1/16 steps. Microstepping provides smoother operation and higher resolution, but it does not automatically increase the mechanical positioning accuracy by the same amount.

Unipolar and bipolar
Stepper motors can be either unipolar or bipolar. Bipolar motors normally have two separate windings and four connections. The current through the windings must be able to change direction, so a suitable stepper motor driver is required. Unipolar motors have windings with center taps and often have five or six connections. The appropriate type depends on the motor design and the selected driver.

Torque and speed
A stepper motor does not provide the same torque at all speeds. Holding torque indicates how much torque the motor can provide while the shaft is stationary and the windings are energized. As speed increases, the available torque normally decreases. A higher voltage supplied to the stepper motor driver can therefore be advantageous at higher speeds.

When selecting a stepper motor, you should not only consider the physical motor size. Motor length, holding torque, rated current, winding resistance, inductance, step angle and desired speed should all be considered together with the specifications of the stepper motor driver.