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Normal or Stepper?
Big, high speed motors need to have a conventional design. Trying to move a really large motor in steps might rip it off its mountings.
Small precision motors with robotic accuracy need to have the stepper design. Accurate position control becomes possible.
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Stepper motors rotate through precise angular steps giving perfect position control.
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Stepper motors are manufactured with steps per revolution of 12, 24, 48, 72, 144, 180, and 200.
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These give shaft rotation angles of 30, 15, 7.5, 5, 2.5, 2, and 1.8 degrees per step.
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Stepper motors come in bipolar and unipolar versions with both 4 pole or 6 pole devices.
7.5o steps 3.75o steps
For more precise control, a stepper motor is needed. These are used when accurate position control is needed. Examples include robotic movement control, printer head movement control and disk drive head positioning.
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They step through a small known angle so it is possible to know the exact angular position of the motor.
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They are usually small.
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They are used for precise movement control in robotics and also in computer printers and disk drives.
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Ideal for controlling small precise movements in either direction.
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Hard and expensive to make very large stepper motors although kilowatt powers are available.
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More complex electronics is needed to control the motor, involving programming, data tables and a PIC chip or microcontroller.
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Accurate control is possible without negative feedback and a closed loop although this is sometimes included for additional safety and reliability.
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Difficult to control at high speeds.
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Poor efficiency converting electrical energy to mechanical.
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The rotation angle of the motor depends only on the input pulses.
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The motor has full torque at standstill if the electromagnets are turned on.
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Precise repeatable positioning is possible without positional drift.
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Excellent start/stop/reverse response.
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Reliable because there are no sliding contact brushes in the motor.
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Easy to build open-loop motor control systems.
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Excellent low speed performance especially with a gear box.
Unipolar Stepper Motor - Five or Six Connections
Connection 1 and 2 are sometimes joined together inside the motor.

Driver Circuit

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Unipolar motors have centre tapped coil windings.
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Only half the coil is energised at any time.
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If current flows from A to 1, the magnetic field will be established.
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If the current flows from B to 1, the field will be reversed.
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Likewise for coil 2.
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Four simple MOSFET switching circuits can be used to drive these coils.
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Bipolar transistors could be used instead.
Bipolar Stepper Motors - Four Connections

To reverse the magnetic field in the coils, an H-Bridge circuit is used. This is more complex than the unipolar arrangement above.

This circuit is able to energise the stepper motor coils in either direction. Two H-Bridge circuits are used, one for each coil.
Stepper Motor Drivers
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Four coil stepper motors can be controlled with four MOSFET switch circuits.
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Bipolar motors need the current to be reversed so H-Bridge controllers are ideal.
A Possible Physical Layout
Here is an approximation of one possible physical layout for a stepper motor. Only two of the eight coils are shown.

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