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Stepper motors are quite
different from ordinary DC electric motors in that they do not rotate in a
continuous fashion, but, as the name suggests, move in discrete steps.
Sometimes these steps are so small that the overall rotation of a stepper
motor is indistinguishable from that of a conventional one. Stepper motors
have a number of advantages over conventional motors in automation and
control systems. Once they have moved to their new position, they can hold
it against any
 applied torque from a load (within their load limits). They
also offer very precise control over position by allowing their control
system to specify how many steps to move in a specified direction and at
what speed. Either on their own or coupled to a belt and pulley drive
system, this makes stepper motors a very powerful and flexible device in
the automation engineer’s design repertoire.
In this guide we will be using a
StepperBee USB adaptor board
to rotate a stepper motor a given number of steps, in a specified
direction at a specified speed using a PC.
The stepper motor used in this example is the type most commonly used in
the majority of medium torque applications. It is a 12 volt, 4-phase,
Unipolar stepper motor with a 1.8 degree step size (i.e. it will do one
complete rotation in 200 steps).
Connecting the Stepper Motor to StepperBee
The stepper motor has 6 wires attached, which are colour coded according
to the following table
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The StepperBee can drive 2 independent stepper motors and, for our
purposes, we will use the control connections for motor 1. These are
connected as shown below
Here we are using a standard 12v DC power supply rated at 500mA which is
more than adequate for our purposes.
One final connection is required and that is simply to connect the
StepperBee to a free USB socket on the PC using a standard USB lead. As
soon as you connect this lead the PC will automatically configure the
drivers to use with it. These drivers are already part of Windows 200 and
XP so there is no need for any separate installation of third party
drivers
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Software
Having connected the stepper motor we are now ready to control it from the
PC. For this you will need to install the AutoStep software that comes
with the StepperBee. Insert the installation disk and follow the , all too
familiar , installation sequence.
Run AutoStep and you will have the display as shown below.
click on image for higher resolution in new window
Although AutoStep has facilities for a wide range of control functions we
just want to make the stepper motor move a specified number of steps in a
specified direction at a specified speed. To do this we will use the
“manual Control” section to the top left of the screen.
Enter 200 in the number of steps box. Enter 20 in the interval box.
Click on the “Run” button.
If everything is okay you should now see the stepper motor do one complete
rotation clockwise in about half a second |
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