Comments on: Stepper Motors, Part I: Confirming Values http://www.neufeld.newton.ks.us/electronics/?p=44 Sun, 08 Dec 2024 17:19:24 -0600 hourly 1 http://wordpress.org/?v=3.1.3 By: Keith Neufeld http://www.neufeld.newton.ks.us/electronics/?p=44&cpage=1#comment-21946 Keith Neufeld Mon, 07 Jul 2008 16:36:22 +0000 http://www.neufeld.newton.ks.us/electronics/?p=44#comment-21946 Eric, you have the disadvantage of coming across this post a long time after it was written, during which time I've written quite a bit more. :-) In particular, I <a href="?p=140" rel="nofollow">switched to using an A3977 stepper controller</a> that uses pulse-duration modulation current control, and <a href="?p=163" rel="nofollow">increased the step rate almost five-fold from 500 to 2300 steps per second using a high supply voltage</a> as you describe. Eric, you have the disadvantage of coming across this post a long time after it was written, during which time I’ve written quite a bit more. :-)

In particular, I switched to using an A3977 stepper controller that uses pulse-duration modulation current control, and increased the step rate almost five-fold from 500 to 2300 steps per second using a high supply voltage as you describe.

]]> By: Eric http://www.neufeld.newton.ks.us/electronics/?p=44&cpage=1#comment-21938 Eric Mon, 07 Jul 2008 10:27:30 +0000 http://www.neufeld.newton.ks.us/electronics/?p=44#comment-21938 There are actually two different configurations to a four wire motor internally, as they actually always have four coils not two as it would appear at first. One way has series pairs and the other paralleled pairs. One obviously requires twice the current to operate than the other, but at half the inductance, for the end result of shorter rise time and faster stepping. Obviously the other delivers twice the coil strength per amp, but won't rise and therefore step as fast at the same voltages. There are two other configs you will run across, six and eight wire. With this size motor the six wire units you will find won't have three coils - they have four just like the bipolars, but each pair has an added center tap. If they have eight, the four coils have taps at both ends, the reason being you can then chose to wire them externally for either of the two common bipolar modes based on your needs, and a couple of other less common ways as well. The oddball five wires you will find use different types of drive logic entirely, and there are several very different types. The one you have seen, one that actually has five coils all connected to each other in a ring with no common at all, and one with five coils arranged in a star config joined at the center. I have no idea how those work, but I guess someone figured it out.... While the 2.1v number you calculated is correct, the steppers won't actually run at that. The voltage for steppers is a bit confusing, as they really need a constant current not a constant voltage. The driver will act to limit current for you, and the best voltage for those would probably actually be around 24v-36v depending on what the max the driver chip you are using will handle. Usually its 10-20 times rated voltage to get any reasonable rise time or else you either can't step rapidly enough to be of any use, or you will be stepping way before the coil gets to rise to any strength. Remember that on decel it will act as a generator and feedback a few volts, so don't go quite all the way to the drive chips Vmax or you will magic smoke the drive on decel. Things you don't normally think of working with the smaller steppers on electronics! Full size motion control is a bit different of an animal. There are actually two different configurations to a four wire motor internally, as they actually always have four coils not two as it would appear at first. One way has series pairs and the other paralleled pairs. One obviously requires twice the current to operate than the other, but at half the inductance, for the end result of shorter rise time and faster stepping. Obviously the other delivers twice the coil strength per amp, but won’t rise and therefore step as fast at the same voltages.
There are two other configs you will run across, six and eight wire. With this size motor the six wire units you will find won’t have three coils – they have four just like the bipolars, but each pair has an added center tap. If they have eight, the four coils have taps at both ends, the reason being you can then chose to wire them externally for either of the two common bipolar modes based on your needs, and a couple of other less common ways as well. The oddball five wires you will find use different types of drive logic entirely, and there are several very different types. The one you have seen, one that actually has five coils all connected to each other in a ring with no common at all, and one with five coils arranged in a star config joined at the center. I have no idea how those work, but I guess someone figured it out….

While the 2.1v number you calculated is correct, the steppers won’t actually run at that. The voltage for steppers is a bit confusing, as they really need a constant current not a constant voltage. The driver will act to limit current for you, and the best voltage for those would probably actually be around 24v-36v depending on what the max the driver chip you are using will handle. Usually its 10-20 times rated voltage to get any reasonable rise time or else you either can’t step rapidly enough to be of any use, or you will be stepping way before the coil gets to rise to any strength. Remember that on decel it will act as a generator and feedback a few volts, so don’t go quite all the way to the drive chips Vmax or you will magic smoke the drive on decel. Things you don’t normally think of working with the smaller steppers on electronics! Full size motion control is a bit different of an animal.

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