# What is different about a stepping motor?

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#### shrox

##### Well-Known Member
What is different about a stepping motor from in other electric motors, and what is a "regular" electric motor then? Does a stepping motor have preset RPMs per a certain range of voltage? Is it different than a variable speed motor?

shrox

https://www.cs.uiowa.edu/~jones/step/

i have seen them used in machinery, rotating 1/10 (or some fraction of a rotation) and stopping, only to do it over again. mainly used in automation processes

the link says they can spin fast too, though.

Originally posted by shrox
What is different about a stepping motor from in other electric motors, and what is a "regular" electric motor then? Does a stepping motor have preset RPMs per a certain range of voltage? Is it different than a variable speed motor?

shrox

A stepping motor moves in steps, typically a few degrees per DC pulse, and those pulses can be TTL level (ie. computer bit stream). They *can* spin normally, as long as you keep sending them bits that tell them to step and step and step and step.... They will spin as fast as they're told to, up to the limit of their ability to handle (a) the rotation or (b) the bit stream.

A regular motor can move only a small increment, if you time the power to the rotation very closely, but they're not meant to. They're meant to use the momentum to carry them to the next state where they can be pushed again by the electromagnets.

A stepper is a very special type of motor that moves in discrete jumps. Mind you those can be in steps so small you can't tell the difference.

One thing. steppers require control systems. You do not just apply power and they spin. In some cases there is control logic built into the motor, however that is the exception. Steppers tend to be used where precise positioning is desired. Beware if you hear the the term L4/R used in a stepper drive. Those tend to require big-honking load resistors to dissipate excess power.

Steppers are also primarily used in closed loop systems where there is a position feedback loop. Normally an incremental encoder.

Although I did build a hail-mary system where I counted the steps, calculated how far a screw drive would move an axis and hoped for the best...

Why do you ask? Stepper applications tend to be special purpose. there may be a better solution.

I was just wanting to know the difference, I see them mostly in hard drives.

shrox

The main reason you see them in hard disk drives is position control. While most people would think, and it used to be true, all you need to do is spin a disk, the new era of power management makes this desireable. When your PC goes into hibernation and the drive shuts down, it knows exactly where the platter and head are for a restart.

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