04  Physics of a real stepper motor
Submitted by Webbot on June 10, 2008  10:47pm.
So lets now leave our imaginary world and look at how this
extends to real stepper motors.
Our rotating ‘Bar A’ only had two poles – one at each end of
the bar – and so we only got two steps per revolution. A real stepper motor may
have, for example, 48 steps per revolution and each step would therefore move
through 360/48 or 7.5 degrees per step. How does this happen? Well, rather than
it being a bar, then think of it as a cylinder where every 7.5 degrees the
polarity is either North or South but it always alternates from one to the
other. That’s why stepper motors always have an ‘even’ number of steps. Here’s
what it may look like if we look down on it and there are only 8 steps:
Now instead of one Bar B we actually have two. Each of these
two electromagnets will have a coil around them. To complicate things slightly
there are two different ways that these coils are configured: bipolar,
and ‘unipolar’.
We will look at BiPolar first because it is the simplest to
understand whereas a UniPolar motor has other advantages and disadvantages but
can, when required, be used as if it was a bipolar motor. We will find out why
later.
