8-lead stepper

Hi,

I've got myself 2 stepper motors: datasheet
And I've read the how-to on this site about Stepper Motors, but:

It only talks about steppers with 4,5 or 6 wires, mine has 8. From what I understand I can decide for myself to use it unipolar or bipolar, but what's the correct way to wire them?

I've tried several different ways, but with only 1 which "worked" bipolar:
Out0: red+blue
Out1: rw+bw
Out2: green+black
Out3: gw+bw

The stepper motor worked this way but only at speed 2, at all other speeds it just acted weird, it felt like it was working hard, going half a step back and forward but just wouldn't turn. I understood from the OSC reference that not all steppers can be stepped at 1 step/milisecond but this one works at 2ms and acts strange again when I try 3, 5 or 10 ms (etc.)

Can someone guide me, tell me how I should wire it, unipolar and/or bipolar?

Thanks, G.J. van Trier.

That configuration (bipolar(p)) causes the motor to draw over 1A at 5V.  And that's just one phase.  That right there could be your problem.  You never said how you're powering the motor.  If you're powering it externally, you're still probably going to overload the driver chip, which is only rated for 1A per channel and has derated power handling capability due to being socketed.  If you're powering it from the board's supply, I'd expect all manner of odd behavior, including what you're reporting, due to sags and other glitches feeding back into the power rail.

How you should wire it depends on many things.  I'd at least start out with bipolar(s).  It has the lowest current draw at a given voltage.  As such, it is the least likely to cause power issues.  It will, of course, also deliver the least torque.

Have you tried the following configuration?  It would either work not at all or it would work vastly better.  The difference is in whether the half-windings are fighting against each other or helping each other.  If you've got them fighting each other, the only thing causing any motion at all is imbalance between the windings.

Out0: red+bw
Out1: blue+rw
Out2: black+gw
Out3: green+bw

The wiring for bipolar(s) would then be:
Out0: bw
Out1: red

Tie blue and rw together

Out2: gw
Out3: black

Tie green and bw together

Hi,

Thanks for your reply Lou.

I knew i forgot to tell someting ; )
I am powering the stepper using the external power and a 9/12v 5000mA adapter.

If I connect it bipolar(p), 9v, then it "stutters", 12v runs smooth, but still the same old story, it only works decently at speed 2.
If I connect it bipolar(s) 6v, it works like bipolar(p) 12v (only smooth at speed 2) but I can't stall bipolar(p) 12v and I can easily stall bipolar(s).
The alternative bipolar(p) wiring resulted in it not moving at all.

So, eehm, how to resolve this? If I stack another driver-chip on top of the other, will this odd behavior go away?

Thanks, G.J. van Trier.

And another question ; )

"That configuration (bipolar(p)) causes the motor to draw over 1A at 5V.  And that's just one phase."

What do you mean with "just one phase"? The max amp this stepper can use at one moment is 1.4A while using bipolar(p) right? (unless it stalls) so if I stack the driver chips so the makingboard can use 2A theoretically (minus the capability due to being socketed) I will be able to tame this beast? Or am I missing some information reguarding multiple phasessomething? I'm really new at this

Thanks, G.J. van Trier.

Previously g.j. van Trier wrote:

What do you mean with "just one phase"?

Stepper motors (whether unipolar or bipolar) have windings at two (sometimes three) phases 90 (sometimes 120) degrees apart from each other.  At any given time, one, both, or neither of the phases might be energized.  This motor has two phases (with two coils at each phase).  If both are energized, you're pulling twice that 1.4A from your power supply.

The max amp this stepper can use at one moment is 1.4A while using bipolar(p) right?

At 4.62V, sure.  At a different voltage, you can compute what it's going to be.  Divide by the "RESISTANCE/PHASE" column.  So, for 12V and bipolar(p), you're looking at over 3.6A per phase.  If both are on at the same time, 7.3A. 

That's a lot of current.  You seem to be thinking that the motor limits current to 1.4A by some dynamic means.  It doesn't.  That figure is just the DC current through the winding resistance at a certain voltage.

(unless it stalls)

Right.  And you always have stall current when starting or when changing speeds as well as when trying to move something that's too heavy/stiff.

so if I stack the driver chips so the makingboard can use 2A theoretically (minus the capability due to being socketed) I will be able to tame this beast?

Theoretically.  That's just max per-channel current, though.  Because the transistors in the driver have a nonzero resistance when switched on, some of the current gets turned into heat.  To some extent, the current rating is based on that.  You still must get rid of the heat, though, and that's where the heat sinking comes in.  If you don't, the heat will build up in the device (faster than it can bleed out into the environment) until the thermal shutoff circuitry is engaged and shuts off the driver until it can cool down.

Normally, these devices are meant to be heatsinked via a specially designed PCB which has a large plane of copper connected to the middle 4 pins.  Being socketed means that thermal connection is poorer than it would be if the part were soldered in.  It's a tradeoff.  In the context of this board design, it is more important to be able to replace blown driver chips.

Previously g.j. van Trier wrote:

I am powering the stepper using the external power and a 9/12v 5000mA adapter.

If I connect it bipolar(p), 9v, then it "stutters", 12v runs smooth, but still the same old story, it only works decently at speed 2.
If I connect it bipolar(s) 6v, it works like bipolar(p) 12v (only smooth at speed 2) but I can't stall bipolar(p) 12v and I can easily stall bipolar(s).

I would expect the serial configuration to be easier to stall.  It draws 1/4 of the current at a given voltage and load.

How massive is the rotor on this thing?  And how fast is speed 2?  And how fast are the other speeds that the motor won't run at?  Stepper motors don't like changing speeds.  They lose sync and stop or vibrate until the driven speed and phase match the mechanical ones, and that often only happens at rest.

I'm not sure how to interpret the rotor inertia figure of 275 gcm^2, but the weight of 650g means it (the entire motor or just the rotor, it doesn't say) weighs almost a pound and a half.  I'm assuming you have no load on the motor shaft for this level of testing.

If everything is functioning properly, each phase (I'll clarify that in my other reply) will draw the following currents at 9 and 12V.  These are DC currents based on the winding resistance and the specified voltage.  Stall currents are expected to be significantly higher.

Oh, and if you haven't set the duty cycle to 100%, you probably want to do that.  I haven't run motors on my Make Controller yet, but I've read that it often comes up that somebody hasn't set the duty to 100%, so performance isn't what they expect.

The alternative bipolar(p) wiring resulted in it not moving at all.

That's a bit odd.  It means I'm not reading the datasheet quite right.  Oh well, so long as we know which wiring is correct.

So, eehm, how to resolve this? If I stack another driver-chip on top of the other, will this odd behavior go away?

I don't actually know the cause of your problem (I can only guess from here), but I know what stacking driver chips will do, and am fairly certain that it will not make the behavior go away; at least not in a robust manner.

What that would do is to allow you to pass more current by splitting the current between the paralleled drivers.  You'd also have to figure out how to get rid of even more heat.  I probably wouldn't try doubling without also adding some of those DIP heatsinks and forcing air past them.

Again thanks alot for your reply Lou,

I have learned a lot ; ) and I'm going to test a few things, stacking the driver chips, heatsinking them, getting a new power source and testing with different loads on the shaft. I'll also take a look at how the stepper reacts to <100% duty.

If and when I'll get new results I'll report them here so others might learn from my mistakes

Gr, G.J. van Trier.