Myths About Motor Control – Myth 2

Small electrical motors are ubiquitous. The human environment is being automated in an increasingly fast pace, driven by the desire for safety, security and health, fueled by an aging population in the highest developed countries, gadgets that go mainstream, and by new manufacturing trends that characterize the 4th Industrial Revolution.

Every day, we see new, ingenious applications for small electric motors. And while this series on myths about motor control is supposed to cover all aspects on how to control a motor, the booming market for small motors is quite different compared to the huge industrial motors, meaning there are too many myths out in the world. So, instead of talking about electric motors in general, we’ll focus on myths in the small motor market, tackling one myth a week.

Note that some aspects are true for bigger motors as well.

Myth 2: Stepper motors are inefficient and there is no reason to use them…

Stepper motors are not a good choice if you are looking for the ultimate power/weight or power/volume ratio, or efficiency – you would never choose them to power a flying drone or the joints of a prosthetic arm. So, will they be replaced by brushless servos, sooner or later? Why do engineers choose stepper motors, of all possible solutions?

The answer is quite simple: The stepper motor – usually designed as a 2-phase synchronous motor with a high number of poles – offers high torque at low rotational speed. A hybrid stepper motor typically has 50 poles, that’s kind of a magnetic gearbox. And this enables direct drive systems, which means: You get rid of the mechanical gearbox. A gearbox stands either for gear loose and limited lifetime – or significant cost.

So, in case you design a medical analyzer, a 3D printer or a motorized security camera, the stepper might be just the right choice to enable a simple and reliable design architecture. The stepper motor is a component that is mass manufactured at low cost, but with ultimate precision and – due to the low speed – a lifetime that is de facto unlimited, as the bearings will not wear out.