# Stepper Motor Basics

Discussion in 'Electronic Basics' started by Bill Bowden, Apr 13, 2008.

1. ### Bill BowdenGuest

I have a stepper motor from Airpax, modle C82710 that has 6 wires
connected to 2 windings with a center tap. It's rated at 12 volts, 36
ohms from center tap to the end of the winding, and 7.5 degrees per
step.

I'm not too familiar with stepper motors, but understand the shaft can
be moved in either direction one step at a time. I read some articles
on Google but couldn't find any that showed the necessary signals and
timing to rotate the motor continously in one direction.

I played around with it, and found I could move the motor shaft one
step at a time by just alternating the connection to either side of
one of the windings with the center tap common. But it only goes so
far and stops, and the second winding was not being used.

So, the question is, what is a proper polarity and timing sequence on
the various connections to continuously move the motor in the same
direction?

-Bill

2. ### VaractorGuest

Look here:

http://en.wikipedia.org/wiki/Stepper_motor

Cheers

3. ### Richard SerianiGuest

Bill,

Here are a couple of links that may help. The first will show the drive
sequence required for unipolar and bipolar operation (among other things);
the second will show some methods of doing it.

Lots more on the web. Many manufacturers of driver IC's if you don't want to
use transistors to drive the motors. Also, much good info about controlling
these with microcontrollers or discrete logic.

http://www.shinano.com/xampp/stepper-motors.php
http://www.techlib.com/electronics/stepper.html

Have fun playing with these.

Richard

4. ### Rich WebbGuest

Sounds like you have a uni-polar stepper there. The simplest way to
drive it is just to use four transistors. Apply your 12 V to the
common and setup the transistors to turn on to provide a ground path
for the desired winding. Sequence them in the order A, B, ~A, ~B.

Once you have that part working, you can look into half-stepping (two
phases on at once) and beefier drive circuits (choppers) that control
the current through the windings for higher torque and speed.

http://en.wikipedia.org/wiki/Stepper_motor

6. ### BobGGuest

Or use 2 dpdt toggle switches as a quick visualization tool... switch
them in the order 00 01 11 10 to go one way, reverse switch order to
step the other way.

7. ### Bill BowdenGuest

Thanks, but I'm not sure of the sequence A,B,-A,-B. Suppose I have
both center taps connected to +12 and the other 4 lines are connected
to transistors. The problem is which side of which winding should I
start with? And will the next transistor supply a ground to the other
side of the same winding? An then there is a phase problem dealing
with the second winding? How do I know which side of the second
winding to ground next?

-Bill

8. ### Sjouke BurryGuest

Playing with stepper motors I did the following:
attach both centre taps to 5 volts, and attach
a 10-15 cm piece of wood(I used a shaslik stick)
to the stepper motor axis.
Now ground one of the four wires,and mark the place
pointed at by the stick. Use your hand to damp the motion,
and in this way you get 4 marks close together.
Now just check which wire belongs to one of those
positions, and you know in which order you have to power them.
I connected a 4 channel buffer IC to them, and connected
the buffer to my computers printer port.
I also put 4 leds on those outputs, to be able to
see what my printerport did to those inputs.
For medium force, just energise them 1-2-3-4-1-2-3-4 etc.
For high force, use 12-23-34-41-12-23-34-41 etcetera.

9. ### Bill BowdenGuest

Yes, I drew a little line on the shaft to watch the position and
connected the 4 lines to push button switches so I could ground them
in any order. After a few tries, I found a sequence that keeps moving
the motor the same way. Haven't figured out how to reverse it yet, but
it's a fun game pushing switches to see which way the motor moves.

-Bill