Measurements on a small permanent-magnet dc motor indicate that it has an armature resistance of 4.6. With

Question:

Measurements on a small permanent-magnet dc motor indicate that it has an armature resistance of 4.6Ω. With an applied armature voltage of 5 V, the motor is observed to achieve a no-load speed of 11,210r/min while drawing an armature current of 12.5 mA.

a. Calculate the motor torque constant Km in V/(rad/sec).

b. Calculate the no-load rotational losses in mW. Assume the motor to be operating from an applied armature voltage of 5V.

c. Find the stall current and torque of the motor.

d. At what speeds will the motor achieve an output power of 1 W? Estimate the motor efficiency under these operating conditions. Assume that the rotational loss varies as the cube of the speed.