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Step 13The Stepper Motors
Bipolar motors
There are only two coils, and current must be sent through a coil first in one direction and then in the other direction; thus the name bipolar.
Bipolar motors need more than 4 transistors to operate them, but they are also more powerful than a unipolar motor of the same weight.
To be able to send current in both directions, engineers can use an H-bridge to control each coil or a step motor driver chip.
Unipolar motors
In a unipolar stepper motor, there are four separate electromagnets. To turn the motor, first coil "1" is given current, then it's turned
off and coil 2 is given current, then coil 3, then 4, and then 1 again in a repeating pattern. Current is only sent through the coils in
one direction; thus the name unipolar.
A unipolar stepper motor will have 5 or 6 wires coming out of it. Four of those wires are each connected to one end of one coil.
The extra wire (or 2) is called "common." To operate the motor, the "common" wire(s) is(are) connected to the supply voltage,
and the other four wires are connected to ground through transistors, so the transistors control whether current flows or not.
A microcontroller or stepper motor controller is used to activate the transistors in the right order. This ease of operation makes
unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements.
(For the experimenter, one way to distinguish common wire from a coil-end wire is by measuring the resistance.
Resistance between common wire and coil-end wire is always half of what it is between coil-end and coil-end wires.
This is due to the fact that there is actually twice the length of coil between the ends and only half from center (common wire) to the end.)
www.8linx.com
There are only two coils, and current must be sent through a coil first in one direction and then in the other direction; thus the name bipolar.
Bipolar motors need more than 4 transistors to operate them, but they are also more powerful than a unipolar motor of the same weight.
To be able to send current in both directions, engineers can use an H-bridge to control each coil or a step motor driver chip.
Unipolar motors
In a unipolar stepper motor, there are four separate electromagnets. To turn the motor, first coil "1" is given current, then it's turned
off and coil 2 is given current, then coil 3, then 4, and then 1 again in a repeating pattern. Current is only sent through the coils in
one direction; thus the name unipolar.
A unipolar stepper motor will have 5 or 6 wires coming out of it. Four of those wires are each connected to one end of one coil.
The extra wire (or 2) is called "common." To operate the motor, the "common" wire(s) is(are) connected to the supply voltage,
and the other four wires are connected to ground through transistors, so the transistors control whether current flows or not.
A microcontroller or stepper motor controller is used to activate the transistors in the right order. This ease of operation makes
unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements.
(For the experimenter, one way to distinguish common wire from a coil-end wire is by measuring the resistance.
Resistance between common wire and coil-end wire is always half of what it is between coil-end and coil-end wires.
This is due to the fact that there is actually twice the length of coil between the ends and only half from center (common wire) to the end.)
www.8linx.com
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