For this week’s CNC Talks episode, Jatinder and Ben talked about the differences between a stepper motor from a servomotor. All the things you’ll read are just a few excerpts from the 4th CNC Talks Episode that you can watch here.
The duo shared tidbits based on their experiences from using these two motors and the tools they’ve used and are using. They claim to be no experts but they hope that what they shared will help you in your machining journey.
1. Affordability: What’s more expensive?
Ben from 3dTek is a user of steppers because it is the most cost-effective solution. He hasn’t used much a servomotor since he finds that the stepper is not only cost effective but also finds that its a great system for his requirements.
Straightforward answer, servo motors are more expensive and can be complex to set up.
2. Differences in operation
A stepper motor will move a certain step then stop there and will try to hold that position whereas a servo motor is more like a motor that will just continue to run. When you need to hold the motor in the same position, servos do not have a holding torque, unlike the stepper motor which has that hold function.
So you’re basically switching it on/off at that position, once you achieve that position you’re kind of switching off motor to stay at the desired position.
Sort of yeah but where to hold that position, unlike a stepper that has some holding torque, the servo will move to the position and then provide a feedback to maintain the position so the servo will wait there and if it has any force applied to it that tries to make it move off the position it’ll fight the force, whereas the stepper will move to that position and then spend all that energy trying to hold that position that’s the sort of main difference on how they work. They have very different ways of driving them so you won’t find that you can use servo drive with the stepper or the other way around as they are totally separate technologies and there is a lot more going on generally in a servo motor because they are required to have some feedback to operate the motor, so they have an encoder attached to them.
3. Which is Smoother? Servo or Stepper
Servos are generally smoother because they provide continuous rotation unlike steppers as they move in small steps.
A stepper motor need to move to a position and on or in its either to its next detent (step) or using micro stepping to a position between one of its two detents.
When I say detent if anyone’s got a stepper motor or used one, you’ll notice when you spin the shaft of the motor you feel it lock to the next position almost snaps into position that’s the detent. Most stepper motors will have 200 or 400 of these orientations and you either move from one position to the next or using microstepping you move in subdivided steps to the next position. Whereas a server really has an unlimited in an infinite number positions because there are no positions and driving a servo is often smother, you don’t have some of the issues to do with microstepping that you can come across with a stepper motor.
4. Motor Watts and Torque
How to decide between motor wattage and torque?
Most of the stepper motors are rated in torque (Nm) and Servo motors are rated in watts. To be able to compare both systems together, its a good idea to check the holding torque, running torque and maximum torque of both systems in their datasheets.
Love the general points discussed by Jat and Ben? Listen to the full episode here.
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Enjoy machining! 🙂