The unipolar stepper motor has two windings for each phase, allowing current to flow in only one direction. It is 50% efficient and has a simple scheme with three conductors per phase. It can be controlled easily and used for precise, timed angular motion. The motor produces more noise and vibration but requires less maintenance than a DC motor.
Unipolar stepper is a type of 50% efficient two-phase stepper motor. The unipolar stepper motor has two windings for each phase to allow electric current to flow in only one direction in each winding. This opposes the single-winding-per-phase construction of a bipolar stepper motor, which requires electric current to flow in both directions. The unipolar stepper motor is designated as 50% efficient because it uses twice the amount of wire as a similarly sized bipolar stepper motor, yet energizes only half of the windings at any one time.
This type of stepper motor has the simplest scheme of all two-phase stepper motors. Each phase of the unipolar stepper motor consists of two windings with a common ground, resulting in three conductors per phase. In most cases, the common ground leads of the phases will be coupled inside the motor, resulting in five external leads for a two-phase unipolar stepper motor.
With controlled excitation of the windings via a control circuit, the unipolar stepper motor circuit does not require the brushes used by direct current (DC) powered motors, and the direction of shaft rotation can be changed easily. Using an external control circuit, the energizing cycles of the windings can be timed to allow the unipolar stepper motor to move forward or reverse a precise number of steps. When combined with other technologies, the unipolar stepper motor can be used for creating home robotics, Arduino-controlled projects, and other projects that require precise, timed angular motion.
Since the unipolar stepper motor windings are individually energized using a control loop, the individual windings become magnetically charged. This electromagnetic charge pulls the gear teeth towards the winding and into the radius of the next winding. At this point, the current to the first winding is cut off by the control circuit and directed to the next winding in the series. As current is switched from one winding to another, the gear teeth follow the magnetic field, moving to the next winding where the gear will stop until the process is repeated or reversed.
In a stepper motor, the speed, torque and direction of motion are controlled by the controller circuit, giving these motors a wide range of capabilities. The stepper motor works in single steps, so instead of the smooth rotation of a DC motor, it produces more noise and vibration than comparably sized DC motors. The unipolar stepper motor, on the other hand, requires less maintenance because there are no brushes to wear out and produces controlled, variable motion that is not possible with a DC motor.
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