Stepper Motor Question...

[brentonw2004]

Hello everyone! I would like to first state that this is the first time I have attempted to use a stepper motor. I salvaged two Mitsumi m42sp-5a, https://www.mitsumi-components.com/Catalog/compo/motor/m42sp/5/text01e.pdf , from a Lexmark printer. As far as I could tell by reading the datasheet, the motors are unipolar, 4 phase. I want to drive them from a PIC controller and use an isolator circuit just to protect the PIC. I think I understand the pattern fine, but the wiring of this particular motor has me confused. There are only four wires. Is this usual? I was sorta expecting at least 5 wires, one of the wires being ground and the other 4 being the different windings. I am probably misunderstanding the whole pricliple horribly, so please feel free to correct me. Any pages explaining this any better, especially using a pic/pc to control it instead of constructing a driver circuit. Why would there only be 4 wires?
Thanks!
-Brent

 

[captainkirksdog]

Hi Brent,
I can't tell from the datasheet you provided, but I'd try checking for continuity between the motor case and one of the wires. The case may be acting as the center tap on this one. You should check this source out too, especially the last paragraph. Good luck.

**broken link removed**

 

[Nigel Goodwin]

As it's only got four wires I would suspect it's probably a bipolar motor, as you say the datasheet is very vague!.

The link 'captainkirksdog' posted should be helpful to you.

 

[brentonw2004]

Hello everyone! As I stated before, I'm sorta ignorant about steppre motors, but I did find out a little more by just checking around with a tester. The four wires are all connected as a 4 wire ribbon. The first two have very low resistance, and the second pair has very low resistance. I am taking this to mean that it is a bipolar motor as Nigel suggested earlier. I checked around the motor case trying to find a ground/center tap/whatever, and I couldn't find anything. Is this a bipolar motor? How much harder are they to control than a unipolar? Could I still run it directly from a PIC with an isolator circuit?
Thanks for your replies!!
-Brent

 

[captainkirksdog]

Brent,
If you look at the data sheet page two, line seven, you'll see that it mentions "unipolar". I take this to mean the motor is a unipolar wound device. Don't know for sure, so keep trying.

 

[brentonw2004]

Yeah I understand what you're saying. I saw that it said unipolar also, but I would think that it should act differently on a tester if it was a unipolar. Could this be a flawed datasheet? Where would the center taps be? Also, I have read that bipolar motors usually have only four wires.
Thanks again for you help!!
Brent

 

[Nigel Goodwin]

Yeah I understand what you're saying. I saw that it said unipolar also, but I would think that it should act differently on a tester if it was a unipolar. Could this be a flawed datasheet? Where would the center taps be? Also, I have read that bipolar motors usually have only four wires.

The main problem with bipolar steppers is the more complicated interface required, you need two H bridges to drive it - for a unipolar you only need four transistors, four resistors, and four diodes.

 

[jbeng]

Since you're kinda new to the whole stepper motor thing, here's a link I supplied for an earlier post in one of the other forums. I think it does a pretty good job in describing what steppers are, how they work, etc.
https://www.cs.uiowa.edu/~jones/step/
JB