In an open loop stepper motor controller, there is no feedback going from the motor to the controller, so the controller cannot make any necessary adjustments. This type of controller is effective when the motor is bearing a constant load at a consistent speed, in which case few if any adjustments will ever be necessary. In applications with a variable load or speed, a closed loop motor controller, where feedback is sent back to the controller for adjustments, may be preferable. When an open loop controller is suitable, it is often preferable, in part because of its low cost and lack of complexity.
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