stepper construction

As an alternative, how about tearing down old steppers for parts? Old 5.25" floppy drives are one place to find them. The driver circuitry is right there as well, which might simplify some of your experimenting. There used to be (and probably still is) info on the Web about how to tap into it.

Some years ago I built a simple robot from a couple of old drives, as a project to work on with my then-young nephew. Mounted the steppers from both drives on one chassis, axles sticking out on either side, installed wheels on them, mounted the second controller board atop the first, and wired both to a long cable with a printer port connector on the other end. (Plus an old PSU.) Simple commands in BASIC operated the steppers independently or together for steering, etc.

The nephew had a blast, but is going into automotive technology instead of robots or programming... oh, well!

Best regards,

Bob Masta DAQARTA v7.21 Data AcQuisition And Real-Time Analysis

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I only have a couple of 5.25" floppies and I want them to keep working. I suppose I could go to a computer junking place and see what I could come up with. But eventually, I'd like to build up some Nema 42 frames for some practical applications. So that is where I'm headed in the end. And I won't be doing that with floppy motors. So eventually, I'd need a supplier. Though certainly I can do a lot of learning before that time.

I could also just buy steppers and tear them down. But I'd really like to find a supplier. That's my big goal, right now. But I just can't seem to find more than the one is Switzerland. And they don't supply all the needed parts, so they provide the kingdom that fails for want of a nail, so to speak.

Hehe. Maybe he decided he couldn't compete with you and ever feel good enough about himself? ;)

Anyway, still looking for a supplier. And thanks for any comments, though. Certainly, worth considering until I do find a few. (I can hope I will find them, perhaps.) Someone has to supply the parts that are used by these stepper manufacturers....

Jon

I wsa thinking of doing something like that, only more like the "space crawler" from Major Matt Mason. It didn't have wheels, it had four arms coming out of the shaft, on each side of the vehicle, supposed to be better for climbing over things. I imagined it might make sense to have each side on its own stepping motor, so if stuck one could wiggle via the other one.

Somewhat related, the regional science fair is happening here this week, and as always, it gets no publicity ahead of time. By the time the news covers it, it's too late to go and take in the event.

Michael

Gearmotors would give you a lot more torque for the size of the package than steppers.

(grain-o-salt: I dislike steppers for all but the uses where they are shoo-ins).

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I'm not at all a motor person, other than simple-minded applications like my Bosch motor driver chip... so maybe a dumb-ass question...

Could you use a gear-motor for a _fast_ (12"/sec, one axis) positioner, with loose positioning accuracy, like 0.02" ?? ...Jim Thompson

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I love to cook with wine.     Sometimes I even put it in the food.

I can use a DC motor, of course, _IF_ I add feedback (optical, for example.)

As I understand it, open loop driving steppers works okay for positioning (my application) with the money going into better and better lead screws and backlash nuts. Up to a point where the lead screws are costing LOTS of money to get the increasing precision out of them. Then it's back to using cheaper motors and expensive precision optical feedback ruling for position control. Something like that, anyway.

Torque is great of course. But I'm positioning, as well. Open loop with steppers, given enough torque for the job. Closed loop won't require them, I suppose. But it adds another whole element to the system.

(Shorter term I'm targeting a 12" x 18" x-y platform motion with 10 micron positioning resolution, ±2 micron variation, and perhaps a few kg mass. Longer term will depend on successes there.)

I'd like to learn, though, if there are better ways to see this.

Jon

Except I wasn't interested in real results, just the notion of using some of the stepping motors I have lying around.

I remember the Steve Ciarcia column in Byte where he uses a cordless drill for the source of propulsion.

Michael

Well, a motor could. Depending on how much money you have, how fast you need it to settle to position, how heavy a load, how much friction, and all those other anal-retentive enginering-ish questions, you could maybe go that fast and get better accuracy than that to boot.

12"/sec is a challenging requirement, but think about how fast the carriage on an inkjet printer traverses -- in most cases I'm pretty sure that's not only a DC motor, but a fairly cheap one. (Of course, I'm also pretty sure that the printing is driven off of the carriage position, not the other way around).

As far as a _gear_ motor -- if you drive the process with a lead screw with a 1/10 inch pitch (which is pretty common), that implies 7200 RPM at the screw. You wouldn't be using any gears beyond the lead screw in that case.

You may need to gear things down going from a motor to a belt or to a rack and pinion -- but probably not by much.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com

Well, there is that. If you already have the steppers then the urge to use them gets strong.

You'd still end up with a lighter, smaller, and probably more efficient assembly with gearmotors, though.

A cordless drill _is_ a gearmotor, that's been optimized for a specific use. Take away some of the use-specific stuff, and you still have a really nice rugged gear motor.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com

I was mostly commenting on Michael's notion of using steppers for propulsion -- that's kinda counter-indicated for a stepper.

For medium-precision positioning where speed, size, and power are not the most important variables to optimize, steppers are a good candidate. They're certainly easy to use as long as you never challenge them past the torque that they can deliver.

In your case you're asking for a range:precision ratio of a bit over

70000. That's going to be a challenge no matter what you do, and you may find that nothing that you can do with a single-stage unit and no feedback will work. I leave that as an exercise to the user, however.

The problems that I have run into with steppers have been associated with trying to use them where speed was important, and they were being challenged to deliver lots of torque (mostly for acceleration to meet speed goals). As soon as you apply more torque to a stepper than it can resist, it slips. When it slips, it's average torque goes down almost to the friction of the mechanical assembly (or lower, because it's being rattled electrically). If all you have is a stepper and a precision stop, then at that point you are screwed.

--
My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com

Jon Kirwan Inscribed thus:

Just about every printer has one or more stepper motors, though the HP ink jets tend to use brush motors and encoders. If you want really powerful steppers grab an old photo copier.

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Best Regards: 
                        Baron.

To build a stepper for educational purposes, I'd suggest you get some tin cans and some magnets, and get cracking.

To build your own custom stepper -- I think you're on your own. What do you want out of a stepper motor that you can't get from an off-the-shelf one?

--
Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com

Or, if you're lazy, look to the surplus places. There always seem to be steppers available (probably 'cause they were replaced by gear motors :).

My favorites, although there may be better ones out there:

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My liberal friends think I'm a conservative kook. 
My conservative friends think I'm a liberal kook. 
Why am I not happy that they have found common ground? 

Tim Wescott, Communications, Control, Circuits & Software 
http://www.wescottdesign.com

I'm gradually gathering that assembling your own stepper "isn't done at the hobbyist level" anymore.

I definitely remember watching some club members building their own DC motors for model aircraft -- magnet wire, stators, etc., all laying on a table about the dozen or so people sitting around trying their hand FOR THE FIRST TIME making their own motors to whatever size they wanted. It was very pleasant to watch. At the time, I wasn't involved and didn't care so much. Now I do and now I'd like to be doing that, as well, but with steppers.

Dismantling different motors will probably yield me parts that won't go together right in the end. (Different frames, etc.) And, at my level of ignorance right now, I'm not even sure if I selected all of them with the same frame that I would find I could make up a larger body without some want of a "nail" that wouldn't be there. I suppose I could just go do it. But a supplier of parts would be nice to know about just the same.

But I'm getting the message. No one here knows of a supplier for hobbyist qtys. Which, together with my google difficulties finding one, I suppose says something. It's not done by hobbyists now.

Jon

Education and the ability to build a stepper that is precisely designed for a specific application, no larger and no smaller than exactly needed, once I learn enough to do that.

Jon

The goal is the process of doing, and then doing better, and then feeling a sense of accomplishment when finally able to both apply theory and test the final result for conformance to that theory and to feel a sense of "closure" about it. It's a very nice feeling.

Jon

And you get the power supply too (which are often in the 20 to 30v range). I'd also argue that the driver circuitry is more accessible than from a floppy drive.

There used to be projects in the hobby magazines for using printers (I guess theyw ere dot-matrix at the time) as the foundation of things like plotters. Mostly leave the printer intact. Of course, there was also that gadget for the Apple Imagewriter that looked like a ribbon cartridge, but was a a scanner sensor, so you'd put the paper to be scanned into the printer just like any other sheet of paper, and scan it simply by issuing commands to the printer (I guess something like spaces to advance the "scanner head" then carriage returns at the end of each line).

Michael

I've never heard of anyone making their own stepper motors. Maybe way off in that direction, but never a mainstream thing if it was ever done. Stepper motors were never a real mainstream hobby thing, so there's less reason to build your own.

Need may have been a requirement there. Making tiny motors that were otherwise unavailable. Model building has been like that, the first model airplane that wsa radio controlled was done with a ham license, since there was nothing else, until the hobby became so mainstream that a special radio service/license was created. That goes way back to the thirties, and since it started early as a hobby, it wsa hobbyists who built up the equipment. Likely the commerical manufacturers that eventually came along were started by hobbyists who had the background and saw a wider interest than just the ones who were building everything.

Of course, at one point, motor building was a hobby thing. I remember one article in one of the hobby magazines were someone built endlessly small motors in his home workshop. IN part to show he could.

I don't think there were ever "parts to build stepper motors for hobbyists". People tended to use surplus (which is the same thing as taking apart floppy drives and printers), hoping to find something useful, and if not, then they are buying off the shelf and paying the price.

There was a time when hobbyists were looking to hobby shops, I can remember some articles in Byte about using servo motors from radio controlled modelling for various things. They were trying for off the shelf solutions.

Michael

Don't you need a special 'keeper' so that you don't demagnetize a stepper motor when you take it apart?

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