Stepper Motor ID'ing and hookup

[jaem]

Hello,

I have a motor sitting in my junk drawer, which I am pretty sure is a stepper motor. (I've never actually used one, so I could be wrong, but it seems to fit the description.) The trouble is that I can't figure out what type it is, and thus how to connect it to anything. (And, yes, I'm aware it needs a special driver - I'm planning on using a PIC.) I think it came from a floppy drive, by the looks of it, but I really can't remember.
Lifting off the top (which has a magnetic ring on the inside edge) there are 15 coils attached to a center shaft by three vanes. In between the vanes are the markings "U". "V", and "W". There are eleven connections on a flat ribbon cable attached to it. Connections 1 and 2 appear to be connected together in a long loop of PCB trace arranged in a geartooth pattern around the perimeter of the coils. In between some of the coils (spaced out) there are two surface mount chips marked with ".D" only, with a silkscreened "HU" and "HV" in the V and W sections, respectively. There does not seem to be one marked "HW", however. The PCB is silkscreened with the codes "144L21-01", "[triangle]YG-M3[backwards RU logo]", and "FM5515", from top to bottom. I've looked these codes up on Google, with no luck. Also stamped on in black is the code "6826A", at a right angle to the previous codes, but in the same corner. The whole assembly is mounted on a metal sheet dimpled with a grid of dots, and with the code "K6829AC1" stamped on the back. It is roughly 2"x2", and squarish.

If someone could help me to identify this motor, and/or point me to some info on using it, I would really appreciate it.

P.S. if it helps, I could post pics later tonight or tomorrow if needed (hopefully), although I feel I've described it pretty thoroughly...

[jwax]

Visit http://en.wikipedia.org/wiki/Stepper_motor
Learning something about steppers is the best you'll get out of that one.
Without specs, it's fairly useless.

[jaem]

ok...

is there any way to test the connections on the ribbon cable to determine how to hook it up before? I thought I read something about continuity testing for the coils... I guess the main thing I need to know is whether it's bipolar or unipolar - I have some info that might help me after that. Can anyone tell from my description?

[philba]

yes, there is. First, how many wires does it have coming out? Most common will be 4 or 6. There are others possibilities but lets go with those for now.

4 wires - bipolar
6 wires - unipolar

then label each wire and test for continuity. With bipolar, you should have 2 pairs that are connected. With unipolar, you should have 2 pairs of 3 wires that are connected. there is another trick to determining which wires are connected. Short two of the wires together and if they go to the same coil, the stepper is harder to turn.

Then, measure the resistance between each of the connected wires and write them down. You should be able to find the unipolar center tap this way - resistance between the CT and one end of the coil is 1/2 the resistance of the entire coil. Finally look at the resistance of the full coils. Presuming the rated voltage to be 5V, use ohms law to determine the current capacity of the coil.

[jaem]

Thanks - that's exactly what I was looking for!

Although, for the record, the motor has 11 connections - see my first post for that. (some go to two 4-pin surface mount components with no model number, and where they go from there, I don't know)

I'll try that as soon as I can.

[philba]

11 connections. Hmmm, it could be some of them are from a quadrature encoder (3) and then there may be 4 independent coils that you can join into a bipolar or unipolar configuration. buzz out the lines to see what's connected. Then try shorting each connect pair together and turn the motor like I said earlier.

the quad encoder ones should have no effect. on the quad encoder lines, 2 will be switches and one will be ground. you should see resistance go from 0 to infinite between a switch and ground as you turn the motor. the two switch lines should be 90 degrees out of phase.

If that's not it then I'm out of ideas...

[jaem]

thanx - I'll try that

[rshayes]

This sounds like a three phase motor (3 vanes, 15 coils). It could still be a stepping motor, but three phase stepping motors are quite rare.

Most stepping motors do not have internal electronics. The surface mount chips mentioned could be diode arrays for transient suppression. Another possibillity is that they are driver chips and that this is really a brushless DC motor, which often has the electronics inside the motor case.

[Chris Smith]

I had a similar one to that complete with optical encoders.

[jaem]

...I did get results for 3-phase steppers when I Googled something like "stepper motor u v w" (the markers on the three coil groups), but I couldn't find anything relevant. (...maybe because they're rare?)

[haklesup]

That's because it may be a Synchronus motor. Try searching on just "motor U V W" or "U V W poles"

When you turn the shaft, do you get thaty clicky, detent, gear-like feel or does it turn smoothly?

This looked helpful, see section IX.
http://www.servo-motors-controls.com/PM ... iables.htm

[jaem]

Ok, I've buzzed it out with the meter... here are my results.

-connections 11, 10, and 9 are all connected (I can't see where they go, but the continuity tester confirms it)
- they are all thicker traces than the rest
- there is about 5 ohms between each pair made from the three connections

- connections 7 - 3 with reference to 8 all give a reading on the diode setting of roughly 0.230V (or a little higher), so I'm guessing rshayes is right about th e diode arrays. I only found that out because the buzzer is on the diode setting

-connections 1 and 2 are plainly visible. They loop together around the perimeter of the coils in a double-edged geartooth pattern. They are not connected to anything but each other.

I tried shorting the connections and didn't notice any difference in it's motion. (I didn't try the possible diode connections or conn. 1 and 2, because it seemed pointless, and holding multimeter probes on 1mm pitch flex cable isn't fun!)

[jaem]

When you turn the shaft, do you get thaty clicky, detent, gear-like feel or does it turn smoothly?

it's clicky...

[rshayes]

It sounds like a three phase motor. Pins 9, 10, and 11 may be the drive windings. These might be cinnected in either a star or delta configuration. The fifteen windings are probably connected in three groups of five each.

The two chips may be some form of hall effect position sensor. They don't appear to be connected to the drive windings.