Many engineers may stumble upon this question when specifying a motor for an application; should I use a Stepper or a Servo motor?
Both stepper and servo motor are excellent but, what’s really important is understanding their capabilities. The simplest way to understand the difference is to consider speed. Servo motors are better for high speed applications while stepper motor are better for low speed applications. Let’s take a look at a simple example of belt drive application.
From the example above, let’s assume below are our requirements:
Travel requirement: 2500mm/sec
Stroke: 2 meter
Load: 1 Kg
Motor Sizing Example Results: (Sizing result is based on pulley diameter on the belt drive system)
Before you can select a stepper or a servo system, you’ll first need to know what the motor requirements are for your application. You’ll need to calculate inertia, required torque, and required speed. You will also need to add safety factors for the required torque calculation.
As an example, let’s say the required speed for this application is 2871 r/min, and the required torque is 3.117 lb-in, or 48.87 oz-in. Based on these needs, let’s compare a Nema 23 size servo and stepper motor side by side.
As you can see from the speed toque curve above, Stepping motor would have a higher starting torque at low speed, but as speed increases, the torque curve falls. Comparing it with the servo motor torque curve, the servo motor might not have a high starting torque, but a servo system maintain its torque quite well at higher speed, which is why for a high speed positioning application a servo system would be preferred.
By plotting on the charts where our application falls on the torque curve, we can highlight the difference in system performance for our high speed application. This identifies that the best choice for our application would be the Servo motor. Using a stepper would leave no safety factor for the application as a servo system would. As listed above our torque requirement is 48.87 oz-in.
If you have any additional questions regarding stepper or servo motors, the MISUMI Engineering Team is always ready to help and available at engineering@misumiusa.com.
