Stepper motor: what moves a 3D printer

How a stepper motor works

A stepper motor is an electric motor whose rotor advances in fixed steps, normally 1.8 degrees, which is 200 steps per revolution. The control electronics send pulses to the coils, and the motor turns exactly as many steps as pulses it receives.

Chips in the driver also divide each step into smaller parts (microstepping), which makes the movement smoother and quieter. That is why positioning does not have to rely on a sensor, and the printer knows where the head is even when it cannot see it.

Where they are used in a printer

• Head movement. On a CoreXY, two motors move the head on the X and Y axes through belts.
• Bed lift. Another motor or motors move the bed on the Z axis.
• Filament feed. A small motor in the extruder pushes plastic into the hotend with an accuracy of fractions of a millimetre.

When a motor fails and what it means

If a motor gets too heavy a load, it skips a step and the printer does not know. The whole rest of the print then shifts, which is the typical layer shift: the top of the part is offset from the bottom. The cause is usually too high a speed, a snagged head or a loose belt.

For you that means a faulty part should be obvious at first glance. On a finished part, look for regular steps on the sides. We photograph every batch before dispatch, and if you are not happy with a part, write to jakub.novak@boostello.com. How the head moves is described under CoreXY.

Servo motor or stepper motor

A servo motor can also control position, but unlike a stepper it has a sensor that checks where it has really turned and corrects its error accordingly. It is more accurate and more powerful, but also much more expensive. That is why consumer 3D printers mainly use stepper motors.

A closed loop does appear with steppers too, those with a magnetic sensor. Some printers use it so they can catch a skipped step. For the customer it makes no difference, what matters is the result.