Which method easily controls speed in DC motors?

Which method easily controls speed in DC motors?

• A. Increase drive current
• B. Change rotor inertia
• C. Vary voltage to adjust speed
• D. Install a higher gear ratio

Answer: (C)

Speed in a DC motor is controlled by the voltage applied to the armature. Increasing the supply voltage raises the motor’s steady-state speed (and decreasing it lowers speed), while keeping the voltage constant makes the motor settle at a speed determined by the balance between back-EMF and load. Torque, on the other hand, is governed by current, so changing current mainly affects torque, not direct speed control. Changing rotor inertia only affects how quickly the motor accelerates or decelerates; it doesn’t set the steady speed once things settle. Installing a higher gear ratio changes the speed seen at the output shaft and trades torque for speed mechanically, not through electrical control. So varying the voltage (or using PWM to adjust the average voltage) is the simplest and most effective way to control DC motor speed.

Speed in a DC motor is controlled by the voltage applied to the armature. Increasing the supply voltage raises the motor’s steady-state speed (and decreasing it lowers speed), while keeping the voltage constant makes the motor settle at a speed determined by the balance between back-EMF and load. Torque, on the other hand, is governed by current, so changing current mainly affects torque, not direct speed control.

Changing rotor inertia only affects how quickly the motor accelerates or decelerates; it doesn’t set the steady speed once things settle. Installing a higher gear ratio changes the speed seen at the output shaft and trades torque for speed mechanically, not through electrical control. So varying the voltage (or using PWM to adjust the average voltage) is the simplest and most effective way to control DC motor speed.