using parts from old/scrapped hardware

Stepper motors aren't particularly hard to control once you understand them. There are tons of reference material out there, so I won't go over them here. For instance,

Thanks Chris for the link (I will book it). And I agree with you - yet you might end up with some of them were you don't know the wiring, voltage or other parameters - which might come handy otherwise if it's documented.

What about various interfaces used? For example in a hdd I know that you can play with machine codes/assemble (I used to do it many years ago) and control the position head or even the motor. Now probably not much changed and this could come handy as well for various applications. So there should be places on the net where people posted their "hacks" on different interfaces. Any idea?

Larry

Determining the type of stepper motor is trivial (for me anyways). All you have to do is probe the terminals with a multimeter, and graph the resistances you find. That graph should match one of the types of motor.

I'm not sure what you mean by "interface". Stepper motors have a pretty standard means of control. You simply energize one coil at a time to make the motor rotate a certain number of degrees, known as a "step". Of course, knowing which coils to energize is why you need to know which kind of motor you have. All this is documented on the net. Several sites even sell prebuilt stepper motor controllers or ICs that incorporate most of the functionality already.

Personally, I prefer servos. Not as precise as steppers, but their encapsulation makes them far easier to use.

I tried using a multimeter with a small stepper motor that I found in an old floppy disk drive. I found that I was able to tell which two wires make a pair, to send a current through one coil.

But I don't know how to tell what voltage the motor should use. Is there any way that I can discover this?

What happens if I use too high a voltage? Will the motor still work OK?

(I'm new to robotics and electronics. I'm a programmer.)

-- Martin Sondergaard, London.

It's not uncommon to run stepper motors at over their rated voltage. What burns out steppers is current. This is why the better stepper drivers use chopping or some other form of current limiting. My favorite find is a 5 volt stepper, which I ran at 12 volts in order to get extra torque. Steppers aren't all that good for drive locomotion over uneven ground, so any added torque is welcome.

Since the steppers from old hardware is basically free or very cheap, there's not much to lose if you try running a 5 volt stepper at 12 volts. If it gets VERY hot (not just pretty hot, which is normal), try lowering the voltage or current.

-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza

Mart> I tried using a multimeter with a small stepper motor that I found

Like the man said- limit the current. Other than that you might find that a lot of floppy disk drives use bipolar as opposed to unipolar stepper motors. Generally 4 wires vs. 6wires respectively. Sometimes you may have 5 wires on a bipolar and 5, 8, (or 9) wires on a unipolar. A few of the fancier steppers will have tach, position, and thermal sensors built in for even more wires. Rare but out there- and I do mean ooutthere$$$$- usually labeled SERVO in some manner. Then there's AC Servos... Then there's the VR(variable reluctance) that are used for platter drive ... many to ridiculous number of phases, used to spin the disk, or tape reel as the case can be. Even the term VR is generic as it can be applied to the stepping motor as well - PM Hybrid VR. Which should imply something ... don't care to remember why right now. Not trying to confuse but not all motors with a certain number of wires fit in any particular category. Anywho (sic)... You're generally ( there's that damn word again) safe with the head positioning motors of old drives particularly floppy, in being a stepper. The unipolar aka bifilar, four phase center tap per pair, is driven by sinking (grounding) one of four lines that are not the CT (center tap) in sequence. The CT of both winding is generally held at a high positive level often with current limiting. It's about the simplest. Not to say things can't get complicated. The bipolar stepper motor, two phase, requires reversal of current for its step sequence. If you only have four wires it's probably bipolar. This is usually implemented by two full H-bridge or two half H-bridge and a split supply. What's an H-bridge? Ummm... look through the links.:)

See if any of these might help:

As for 'hot' just keep a bottle of liquid nitrogen around:P. Hell on the bearings and magnets tho'. Fire extinguisher couldn't hurt. And watch out for that nasty resonant frequency. All hail the magic smoke. Motorola, SGS-Thompson, PICmicro, also have stepper tutorials but I don't have direct links at the moment. Probably should put this as a web page but that would be so uncharacteristic.

Have fun damnit.

"Gordon McComb" wrote in message news: snipped-for-privacy@gmccomb.com...

Like a wiki ;)

Will.

Ummm....maybe! I have yet to see two authoritative sources on stepper motors fully agree on the details. There's even disagreement about what makes a "2-phase" and "4-phase" motor. You'd think they'd have this stuff figured out by now. Probably the most useful wiki on stepper motors would simply be Doug's list of URLs to what other people have written about them. And you'll note that in some critical areas these sites don't agree either!

-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza

Yes, It's on the way. I've downloaded and installed twiki - now I working around to customize a little - such setup some categories to start with

and get the twiki/wiki doc handy and some sort of guide/agreement to start/comment on it on how to organize the stuff around. I plan to have it ready to use this

coming weekend. I will also set scripts to archive regularly the site and provide the archive if you want to download them locally or either mirror them.

Well, there will always be arguments, even on more obvious/straight forward things. But that is for the news groups/boards discussion threads. For the site we should try to keep it down to basic facts as measurements, experiences - centralized and categorized. With an ok search engine on top(as twiki has) - I will say it will make a handy tool for us to progress faster and cheaper in our projects. Or maybe I am wrong?

Larry