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  1. #1
    3D Printer Noob
    Join Date
    Aug 2017
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    Electric motor for 3D printers inquiry

    Hi guys! What makes stepper motors better than servo motors for 3D printers? If I have understood this article ( correctly, below are the main takeaways between the two:

    Stepper motors have the upper hand in availability, cost, easier drive control, but falls short when it comes to resonance if not controlled right;

    On the other hand, servo motors are available in AC and DC drive, never suffer from resonance issues, better used in high speed applications, but they do fall short when it comes to ease-of-use and price.

    Because of that I'm thinking about going for this stepper motor, but I'm very much open to your suggestions, especially suggestions best suited for those who are just starting out.

    Thanks in advance!

  2. #2
    Super Moderator
    Join Date
    Nov 2016
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    Stepper motors are not your typical motor. It is actually a "degree stepper". Normally, there are 200 steps per rotation. These steps are based on where you have 2 coils highly energized to "lock" the motor in position. You then de-energize these coils and energize the alternate pair of coils and the motor "steps" to that position. When managed with a controller, you can mimic rotational control. In fact it is a series of steps to the next position.

    The real power of a stepper motor is in the encoder. These maintain "sub-steps" by controlling all 4 coils. Now you have the possibility to control 1 rotation to 2,000 specific positions. This represents a 10:1 micro-step. Some encoders will divide these even further, and some motors have more full steps or more coils.

    This all runs into a timing problem eventually because clock rates are also involved. You can only send so many pulses in so much time. That is where stepper motors can run out of headroom. Say you have very highly accurate angle control. You have to send, say 11,200 pulses for a single rotation. If you need to drive the system very fast, you have a huge data stream. The system's clocks have to be capable of keeping up with it. The downside to precision is the lack of torque at speed depending on the control algorithm you've worked up.

    In 3D Printer applications, stepper motors have a couple of advantages; one being that they can hold still while energized. This is like a locked motor. Their torque curves are reversed from servo motors. Slow rotation means more power for stepper motors. Servo motors speed up and become more powerful as you provide more energy. that also means your shaft has to rotate. Not very useful when you need a hold a tray at a specific z-depth on a belt drive. Lead-screw z-depths are actually held with very little torque since the lead-screw rarely has enough reverse torque to drive the motor. In the case of a z-depth lead-screw, servo motors do work well.



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