[thanhvu94]

Hi guys,

I'm working on the motors during this semester, and I have an assignment like this:

How to identify whether a motor is a stepper or AC servo motor w/o open the inner parts (recognize it through its shaft, cover, fan, base... only), because they look almost the same for newbies?

From what I have found out so far, the only difference is the diameter of the shaft, and stepper motor doesn't have an encoder while AC servo always has one. .

Thanks.

[mactec54]

Hi guys,

I'm working on the motors during this semester, and I have an assignment like this:

How to identify whether a motor is a stepper or AC servo motor w/o open the inner parts (recognize it through its shaft, cover, fan, base... only), because they look almost the same for newbies?

From what I have found out so far, the only difference is the diameter of the shaft, and stepper motor doesn't have an encoder while AC servo always has one. .

Thanks.

An AC servo will only have 3 phase wires, and a Ground, as stepper motor will have wires 4 6 & 8 wires there are other stepper wiring arrangements as well this is the most used, Steppers can also have encoders as well, so don't get caught with that

Steppers can also have the same diameter shaft, it will depend on the power of the motor as to the shaft size/diameter

[thanhvu94]

An AC servo will only have 3 phase wires, and a Ground, as stepper motor will have wires 4 6 & 8 wires there are other stepper wiring arrangements as well this is the most used, Steppers can also have encoders as well, so don't get caught with that

Steppers can also have the same diameter shaft, it will depend on the power of the motor as to the shaft size/diameter

Thank you so much. Is there anything else besides wiring? (the cover, the base). Or there is no other differences?

And I also have such a huge question. Stepper can run very hot when operating, why there is no cooling fan/heatsink for it?

Thank you.

[James Newton]

And I also have such a huge question. Stepper can run very hot when operating, why there is no cooling fan/heatsink for it?

Very good question. I often wonder why people don't put CPU coolers on hot running stepper motors. It helps enormously. Stepper motors can lose a significant percentage of their max torque when hot.

[ger21]

Because the heat doesn't hurt them, so why bother?

[James Newton]

If heat doesn't hurt them, then why do all stepper motors have a maximum temperature rating? Why did NEMA bother to come up with Class ratings for max temp? Why did Curie find the temperature at which magnets lose their magnetism?

Stepper motors /generally/ aren't hurt by heat under normal operating conditions. But they can be. And they DO lose torque as they heat even in normal operation. Perhaps as little as 5%, but sometimes more depending on the quality of the magnets used in the motor.

More detail and references:
techref.massmind.org/techref/io/stepper/heat.htm

[vmax549]

Ac servos can have a lot more wires

3 phase wires
4-6 hall sensors wires
3-5 encoders wires
2 brake wires
2 posible temp sensor wires

DC servo
2 phase wires
3-5 encoder wires

Most of the time with servos teh phase wires are in a seperate group so there are 2 connectors or wire groups coming out of the body