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The specialist of small precision motors - ORIENTAL MOTOR (INDIA) > Technical Support > Technical Question 4
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Mr. Vex:My customer asked me why
there is no output power displayed (wattage)
for stepping motors. I am trying to find out why.
Miss Ori: Of course, prepare to note it down. The reason
why there is no output displayed in stepping
motors is because there is no concept for rated
speed for stepping motor.The output power displayed with wattage for AC motor and servo motor is when it is driven at rated speed. This is called "rated output power". Since the output in wattage is calculated from formula. It can be theoretically calculated for stepping motor. However,as there is no concept of rated speed for stepping motor, rated output or output power in wattage cannot be displayed.
Mr. Vex:What is the formula for output power then.
Miss Ori: Formula to find output(wattage)="output power = rotating speed x torque x constant number"
 Rotating speed: The number rotating for a certain amount of time. Torque: Torque generated at rotating speed. That is why the output power calculated(Wattage) varies according to the value of rotational speed. For instance, let's calculate based on the 5-phase stepping motor unit of RK Series RK566AA "Speed- Torque characteristics" chart.(see chart below) That is why the output power calculated(Wattage) varies according to the value of rotational speed. For instance, let's calculate based on the 5-phase stepping motor unit of RK Series RK566AA " Speed- Torque characteristics" chart.(see chart below) 1) Calculation is based on 1000 r/min as rotational speed and 0.5 N.m* as torque: 0.1047 x 0.5 x 1000=52.3 W 2)Calculation based on 3000 r/min as rotation speed and 0.2 N.m* as torque: 0.1047 x 0.2 x 3000=62.8 W 
Mr. Vex: So, the output varies with different rotational speed even for the cases of the motor like brushless DC and servo that has flat-torque characteristics.
Miss. Ori:Yes, let see it with brushless DC motor, BX Series BX230 A-A this time. It's rated output is 30W as stated in it's specifications in the catalog, and torque is 0.1N.m no matter what the rotation speed is 1000r/min or 3000r/min as in speed torque characteristics.
1) If it's calculated with rotational speed as 1000 r/min : 0.1047 x 0.1 x 1000= 10 W, it is less than 30 W 2) If it's calculated with rotational speed as 3000 r/min : 0.1047 x 0.1 x 3000= 30 , it is 30 W.
Mr. Vex: I am more confused now. Output power varies by the speed even though the motor with flat torque characteristics?
Miss. Ori: The issue here is, how is the value to assign this rotational speed? The solution key is the concept of "rated speed". This rated speed is stated in the specifications of AC compact motor, brushless DC motor and AC servo motors.
- AC compact standard motor(5IK40GN-AWJ)
-1250 r/min at 50 HZ and 1500 r/min at 60 HZ
-Brushless DC motor:3000 r/min( It may differ in some products, i.e AXH Series and HBL Series)
-AC servo motor: 3000 r/min
Torque generated at rated speed is assigned into the calculation formula to get the output power. This output is stated as "rated output power (wattage)* in the catalogue specifications.
Mr. Vex: I see!!!
Miss. Ori:Yes, and when you have a customer who wants to know the stepping motor output in wattage, you can tell them about this calculation formula. One thing you must inform them is that the output power in wattage comparison is not feasible, when they say " i want to replace the servo motor of XXW to the stepping motor of same wattage". Servo motor and brushless motor especially , have the "peak torque" which does not exist in stepping motor.
Mr. Vex:I understand. When it happens, i will introduce our motor sizing service to ensure our customers will use our products with confidence.
Miss. Ori:Exactly. Vex. keep it up. Introduce the most suitable products to our customers.
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