Fairly basic questions re stepper motor wiring!

[HankMcSpank]

Ik, I'm new to stepper motors, but not to general electronics (in other words I can handle a multimeter, oscilloscope ok).

I've sourced some stepper motors out of some old dot matrix printer. Their spec is identical to the picture number 5 on this page....

http://www.engadget.com/2006/06/29/h...achine-part-1/ (ie 3V & 3.5 ohms & 1.8 deg)

My first problem was working out the wiring, so I followed the guide here...

http://www.doc.ic.ac.uk/~ih/doc/stepper/others/

ok, so now I know which is coil 1, coil 2, coil 3 & coil 4 for my stepper motors.

But my stepper motor driver board's instruction manual, doesn't talk of indiviual coils, it talks of A+ & A- and B+ & B-

Now, then using this earlier guide/diagram...

http://img178.imageshack.us/my.php?i...9518717hy3.jpg

In my situation, coil 1 = red wire, coil 2 = blue wire coil 3 = beige wire, coil 4 = yellow wire

How do I wire up to reflect this driver board instruction manual

http://img381.imageshack.us/my.php?i...1431289ho5.jpg

I'm figuring....

A+ is coil 1 (red wire) A- is coil 3 (beige wire)
B+ is coil 2 (blue wire) B- is coil 4 (yellow wire)

Is this right?

Ok, now what should happen when I connect the stepper motor to the driver board & power it up? (I'm only connecting the x axis for now)

Should there's be a hum from the motor, silence ...what?

Final question my driver board manual talks of setting the axis current - how do I determine what this should be for the motor I mentioned above?! (I'm assuming that becuase the motor spec says 3V & 3.5 ohms ....then I=V/R, therefore 0.86A?)

many thanks.

[irving2008]

Your stepper driver board is expecting 4 wire bipolar motor, i.e. 2 coils A and B two wires per coil + & -. (the diagram in the manual shows a 6 wire which can be wired as bipolar or unipolar, they just don't use the centre taps).

Your stepper is a 5 wire quad coil - a 4-phase unipolar motor. I don't think that this can be used with that driver unless you can isolate the coils to get 8 wires and then pair them up to create effectively two single coils. It is essential that you get the phasing right so that the coils are working together and not against each other. You must separate the windings or you run the risk of frying your driver chips/output transistors

The ratings given are for one coil. Once separated you have the option of wiring in series or parallel to give ratings of 6v, 7ohm (.9A) or 3v, 1.75ohm (1.7A)

[jamesl]

Dot matrix printer motors are fine as a learning curve, but if you are thinking any serious engraving or routing, they just don't cut the mustard.

[HankMcSpank]

Originally Posted by irving2008 Your stepper driver board is expecting 4 wire bipolar motor, i.e. 2 coils A and B two wires per coil + & -. (the diagram in the manual shows a 6 wire which can be wired as bipolar or unipolar, they just don't use the centre taps). Your stepper is a 5 wire quad coil - a 4-phase unipolar motor. I don't think that this can be used with that driver unless you can isolate the coils to get 8 wires and then pair them up to create effectively two single coils. It is essential that you get the phasing right so that the coils are working together and not against each other. You must separate the windings or you run the risk of frying your driver chips/output transistors The ratings given are for one coil. Once separated you have the option of wiring in series or parallel to give ratings of 6v, 7ohm (.9A) or 3v, 1.75ohm (1.7A)

Oh dear - I read their spec that "6 wire motors can be used" & bought the driver board on that basis.

I need to delve a bit more!

If you read page 4 of the driver board guide...

http://www.easy-cnc.com/web/download...3Axis(NEW).pdf

The manual says that 6 wire motors can be used (albeit, it didn't say unipolar or bipolar!). I'm hopeful here because I have two common wires (as opposed to one common wire).

this is how I think my unipolar stepper motor is wired....

http://img58.imageshack.us/my.php?image=68681830sc4.jpg

ie if you ignore the common centre tap in each coil above, then there are two coils above wired series? but can I assume these two coils correlate with rotational bearing in this diagram http://img297.imageshack.us/my.php?image=79496882ht7.jpg[/url] )

[irving2008]

Originally Posted by HankMcSpank Oh dear - I read their spec that "6 wire motors can be used" & bought the driver board on that basis. I need to delve a bit more! If you read page 4 of the driver board guide... http://www.easy-cnc.com/web/download...3Axis(NEW).pdf The manual says that 6 wire motors can be used (albeit, it didn't say unipolar or bipolar!). I'm hopeful here because I have two common wires (as opposed to one common wire). this is how I think my unipolar stepper motor is wired.... http://img58.imageshack.us/my.php?image=68681830sc4.jpg ie if you ignore the common centre tap in each coil above, then there are two coils above wired series? but can I assume these two coils correlate with rotational bearing in this diagram http://img297.imageshack.us/my.php?image=79496882ht7.jpg[/url] )

If your motors have 2 'common' wires and you separate these do you have two completely isolated sets of three wires that have some low resistance to two and ONLY two other wires? If so then you will be able to use it. If, on the other hand there are more than 3 wires that have some connectivity you wont.

Assuming you can separate the two commons to give 6 wires, do the following:
a/ Pick a 'common' wire, label it #1. Measure resistance to all other wires. If you have only 2 other wires that seem to be connected to this one label them #2 and #3. If not then give up because you can't isolate the coils (unless you can open the motor case) and find a better motor.

b/ If the resistances are the same from #1 to #2 and #1 to #3 then you have one coil and #2 and #3 are the ends, #1 is the centre.. The resistance between #2 and #3 should be twice the resistance between #1 and #2 or #1 and #3 (with me so far? ). If not then #1 wasn't the common, so find the pair (out of #1, #2 and #3) with the highest resistance between them and those are the ends of the coil, so relabel them #2 and #3 and the remaining one becomes #1.

c/ Repeat a and b for the other 3 wires, using labels #4, #5 and #6.

d/ The result should be 6 wires, labelled #1 thru #6 where the resistance between #2 and #3 is the same as that between #5 and #6 and wires #1 - #3 are isolated from #4 - #6. If not, give up and find a better motor.

e/ Assuming all the above wire #2 to A+, #3 to A-, #5 to B+, #6 to B-. This should get the motor turning. The current limit should be set to 3v divided by the resistance between wires #2 and #3.

f/ if the motor turns in the wrong direction you can either correct this in the software or swap either wires #2 and #3 OR #5 and #6 over (but only one pair, not both).

Hope that's helps and is as clear as mud

[HankMcSpank]

Originally Posted by irving2008 Assuming you can separate the two commons to give 6 wires, do the following: a/ Pick a 'common' wire, label it #1. Measure resistance to all other wires. If you have only 2 other wires that seem to be connected to this one label them #2 and #3. If not then give up because you can't isolate the coils (unless you can open the motor case) and find a better motor. b/ If the resistances are the same from #1 to #2 and #1 to #3 then you have one coil and #2 and #3 are the ends, #1 is the centre.. The resistance between #2 and #3 should be twice the resistance between #1 and #2 or #1 and #3 (with me so far? ). If not then #1 wasn't the common, so find the pair (out of #1, #2 and #3) with the highest resistance between them and those are the ends of the coil, so relabel them #2 and #3 and the remaining one becomes #1. c/ Repeat a and b for the other 3 wires, using labels #4, #5 and #6. d/ The result should be 6 wires, labelled #1 thru #6 where the resistance between #2 and #3 is the same as that between #5 and #6 and wires #1 - #3 are isolated from #4 - #6. If not, give up and find a better motor. e/ Assuming all the above wire #2 to A+, #3 to A-, #5 to B+, #6 to B-. This should get the motor turning. The current limit should be set to 3v divided by the resistance between wires #2 and #3. f/ if the motor turns in the wrong direction you can either correct this in the software or swap either wires #2 and #3 OR #5 and #6 over (but only one pair, not both). Hope that's helps and is as clear as mud

Thanks for the comprehensive post. I'd actually got to where you're describing prior to posting. By this, I mean I'd established I have a stepper motor with two separate 'center tapped' coils.

Here's a graphical representation of the coils with your numbering scheme...

http://img512.imageshack.us/img512/3212/coilyn3.jpg

the main thrust of my line of question (having established two individual center tapped coils) was - which ends would be A+ & A- & which ends of the coils would be B+ & B-, but you've answered that above - tks!

Earlier today, I gave this a quick go using a trial version of Kcam4. When I go onto the CNC control page & click the right arrow, after about 10 seconds the motor physically rotates one step clockwise - is this right?

Time delay aside, at first glance, the motor seems to be turning the opposite way that the KCam4 GUI arrow is indicating...but I guess if the motor was connected to a thread rod, then it could conceivably be right! eg clicking on the right arrow makes a stepper turn clockise which could conceivably move the 'X' table right?

Re the current limit - thanks that's useful info.

Are these fairly weak motors then? ...ie resistance between points 2 & 3 (one coil) is 6.9ohms. 3V divided by 6.9 ohms = 0.43A I had been hoping to have these drive a couple of light (perspex) 18" square X & Y platforms...but if .43A is the most current these stepper motors can handle, that doesn't seem like a whole lot?!

[HankMcSpank]

Ok, two different CNC app (KCm4 & Mach 3) - with both programs the stepper motor seems *very* slow to react.

I've messed with all the acceleration settings.

Could this be my laptop, my PC-.Board cable or the voltage I'm supplying to the stepper board (my stepper board recommends 24V, but says 12V-30V can be used ..... I'm using 16V)

[jamesl]

Go to www.geckodrive.com there is a very good article on stepper motor drives .

[irving2008]

Originally Posted by HankMcSpank Ok, two different CNC app (KCm4 & Mach 3) - with both programs the stepper motor seems *very* slow to react. I've messed with all the acceleration settings. Could this be my laptop, my PC-.Board cable or the voltage I'm supplying to the stepper board (my stepper board recommends 24V, but says 12V-30V can be used ..... I'm using 16V)

I'm guessing here a little but it could be that the motors need a wider pulse than the software is currently configured for. Try ensuring that your controller is set for full step only (if that's configurable) as it might be set up for microstepping and these motors might not like that. Generally higher resistance coils suggest fairly weak motors, I'd guess those from a printer are going to be fractional Nm torque, maybe .2 - .5 at slow speed and it will fall off rapidly as speed increases. Running a higher voltage (typically 5 - 25 x motor rated volts) against the dynamic current limiter improves the torque curve somewhat at higher speed but can't overcome inherently poor motors.

You can measure the torque using a lever (6" plastic ruler) glued fixed to the motor spindle at the zero mark and a string attached at the 10cm mark with a plastic bag as a weight holder on the end. Arrange motor so that when you power up a single coil it keeps the ruler horizontal. Power up a coil (careful not to exceed current limit, so use low voltage as rated) and pour sugar into bag until motor cannot hold it. Measure weight of bag, string & sugar in kgrams = W , holding torque (i.e. torque at near standstill) of motor is then W Nm. It will degrade to maybe 1/10 of that at a few hundred steps/sec.