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I have a retro CNC machine (EMCO F1P) in my garage that I am currently tinkering with. I would like to replace the old motor control but use the existing step motors. Unfortunately the documentation is scarce, and so I decided to pick one motor apart to see if I could learn anything from it.

Turns out it has 10 wires going into it and 10 windings inside. Each winding pack looks like it has only two wires coming out of it. The wiring diagram is the PCB visible in the picture:

enter image description here

So with my limited understanding of step motors I could need some help determining the parameters for this motor. Is it unipolar or bi-polar? How many steps per revolution does it have? How can I find a driver that will work for it, and how would I know which wire goes where?

Thanks!

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  • \$\begingroup\$ You can count the steps, and I think wikipedia (or any online resource) can help you find out what kind of motor it is. Another important parameter is the winding resistance. If you want to replace the driver you should be looking at the driver's guts, not the motors'. \$\endgroup\$ – Vladimir Cravero Apr 3 '15 at 7:28
  • \$\begingroup\$ I want to find a driver that matches these motors and so I need to figure out which motors they are. Actually I went to several online resources including wikipedia without finding a good answer. \$\endgroup\$ – Lennart Rolland Apr 3 '15 at 8:00
  • \$\begingroup\$ I suspect a driver is spec'd through voltage and current outputs, plus motor type, and these are all infos that are easier to get looking at your driver output stage instead of the motors, that's what I meant. \$\endgroup\$ – Vladimir Cravero Apr 3 '15 at 8:37
  • \$\begingroup\$ As vladimir says look at the driver circuit. You wouldn't try and design a car by looking at the road (poor example I know) \$\endgroup\$ – Andy aka Apr 3 '15 at 10:45
  • \$\begingroup\$ I get what you are saying finally. The drivers are really complex. I will leave this question because I think it is a valid one (is it possible to just look at the motor to determine its specs) And maybe post a new question about the driver. Thanks! \$\endgroup\$ – Lennart Rolland Apr 5 '15 at 19:26
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I have tried to figure this out on my own without looking at the drive circuit as a challenge. After finding this article, I now am fairly convinced that my motor is built after a 5-phase design.

enter image description here

The picture says it all really. 10 windings = 5 phases.

So since it is not a 2-phase motor, it is inherently bi-polar as opposed to uni-polar which some 2-phase designs are. Also it will typically have higher resolution than 2-phase motors. For example some motors have 500 steps per rev which gives 360/500 = 0.72° degrees per step. The resolution depends on the number of teeth.

There are many ways to drive it (see article above), and in most respects it is superior to the 2-phase design, except Torque at low speeds.

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    \$\begingroup\$ The actual degrees-per-step will depend on the number of teeth. \$\endgroup\$ – Dan Sheppard Apr 5 '15 at 19:44
  • \$\begingroup\$ I did not know. Will update! \$\endgroup\$ – Lennart Rolland Apr 5 '15 at 20:37
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    \$\begingroup\$ Yeah, basically stepper motors are cunningly arranged so that the little teeth on the rotor and on the stator don't quite line up from one winding to the next, but almost. When you energise them, the windings give a little tug till they all line up, making everything much more magnetic-energily hunky-dory and so inching the rotor round. At this point the teeth on the next winding will be not quite lined up, and so on. So the number of teeth determines how mush of a resolution each little pull is. \$\endgroup\$ – Dan Sheppard Apr 5 '15 at 20:58

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