Historically, stepper motors are not rated by watts like AC motors or servo motors. So...how would you compare a stepper motor to a servo motor or a brushless motor?
The reason why stepper motors are not rated in watts is because there is no concept of rated rotation speed (RPM) for stepper motors.
Why do we need the rated speed?
AC motors and servo motors are rated for maximum power, in watts, at their rated speeds. Since stepper motors don't have a standard rated speed value, Oriental Motor does not show a wattage specification for stepper motors. If necessary, the wattage value can be calculated.
Formula for output watts
Output [W] | = | 2 × π × T × N | ≒ | 0.1047 × T × N |
60 |
= 0.1047 x T x N
0.1047: Constant
T [N m]: Torque
N [r/min]: Rotation speed
How do you choose the rated speed?
Even though there is no rated speed for stepper motors, it's theoretically possible to derive the output wattage from the formula above based on the operating speed. However, the output watts value will change according to the rated speed you choose.
Here's a general reference for other types of motors:
Let's look at some examples.
●PKE566AC motor + RKSD507-AD driver (RKS566AA system) speed - torque characteristics
Let's look at another example. How about comparing servo motors to brushless motors?
●BXM230-A2 motor + BXSD30-A2 driver (BXS230A-A system) speed - torque characteristics
TIP | When comparing stepper motors to either servo motors or brushless motors, keep in mind that servo motors or brushless motors offer an instantaneous max torque for a limited time. Stepper motors typically do not offer this. |
Don't feel like calculating?
Here's a quick reference chart comparing our AlphaStep AZ Series closed-loop stepper motors with servo motors with equivalent output.
Example: AZ series stepper motors
AZ series (standard type) | Servo motor with equivalent rated torque (reference) |
||
---|---|---|---|
Frame size | Part number | ||
42mm | AZM46 | Equivalent to rated torque of 50 to 100W | |
AZM48 | |||
60mm | AZM66 | Equivalent to rated torque of 100 to 200W | |
AZM69 | Equivalent to rated torque of 200 to 400W | ||
85mm | AZM98 | Equivalent to rated torque of 400 to 750W | |
AZM911 |
If you're wondering, here's a comparison of speed-torque curves between a closed-loop stepper motor and a servo motor of equivalent output.
For comparisons of other sizes, please refer to https://www.orientalmotor.co.jp/products/stepping/overview_5/. Sorry, only Japanese is available at this time. I will try to update this post as they become available. In the mean time, please use Google Translate to translate the page.
Also, be aware of the fundamental and performance differences between stepper motors and servo motors. For example, servo motors work best for rigid mechanical setups at high speeds (ie: ball screw), and stepper motors work best for more compliant setups at low to medium speeds (ie: belt and pulley). To learn more, please read this blog post, The Choice Between Servo Motors and Stepper Motors.
Pick the right motor the first time! Contact our technical support engineers for a product sizing consultation.