The Differences Between DC Motors & Stepper Motors
The DC motor and the stepper motor both operate electromagnetically, but their construction and uses differ. With the stepper, the amount of shaft rotation can be controlled by a microcontroller or a driver chip. This allows for precise movements but it sacrifices rotational strength, or torque. The DC motor is capable of greater torque, but control is sacrificed because the shaft spins continuously. The balance of torque and control often determines which motor will be used in a circuit.
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DC Motor Construction
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A DC motor contains a spinning shaft that is connected to a rotor. There are coils of wire attached to the rotor, which act like electromagnets. Stationary magnets, called stators, are attached to the outer, metal housing of the motor. The motor also contains two terminals, called brushes, which connect to the DC power supply. The brushes make contact with parts of the rotor and provide the current to keep the motor running.
Stepper Motor Construction
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In a sense, a stepper motor is the opposite construction of a DC motor. A stepper motor consists of a rotating shaft that is connected to a permanent magnetic disk. It is called permanent because it remains magnetized without electricity. The disk and shaft are surrounded by two or more stationary coils. The stator is a
surrounding casing that remains stationary and is part of the motor housing. The stator is attached to the housing of the motor and when they receive current from the DC power source, the shaft rotates.
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DC Motor Operation
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When current is connected to the brushes, the rotor coils are energized. The coils become magnetically attracted to and repulsed from the magnetic stator. This causes the shaft to spin. The DC motor differs in operation from the stepper motor because the rotation of the shaft is continuous and the speed depends upon the level of current. The greater the current, the faster the shaft spins and the greater the torque.
Stepper Motor Operation
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A digital pulse, or repeated 5V-to-0V alternations, is used to operate a stepper motor. When the stator receives current, the coils are magnetized and they are attracted to/repulsed from the magnetic poles of the disk. This causes the shaft to rotate from a few degrees to a full 360 degrees. In fact, the shaft can be rotated continuously, as in a DC motor. How far the shaft rotates depends upon how many digital pulses are sent to the stator coils. The shaft can be rotated with precision, as long as there are no digital errors or missed pulses.
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