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Stepping Motors

Discussion in 'Electronic Basics' started by Jason S, May 16, 2006.

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  1. Jason S

    Jason S Guest

    Hi,

    I have Stepping Motor and a controller which has variable speed and a
    'Change Direction' push switch. I want to use it to rotate a light back and
    forth at any required speed, without actually having to stop the motor
    (simply by pressing the Change Direction button during constant operation,
    when required).

    Are stepping motors designed to be run this way or is it not recommended? I
    read that with a 'normal' motor you wouldn't do this due to potential damage
    and lots of sparks, but wasn't sure about stepping motors.

    I want some opinions from others on this.

    Thanks.

    Jason.
    Hobbyist
     
  2. Chris

    Chris Guest

    Hi, Jason. If you're rotating your stepper at less than 1 rev./sec.,
    and your stepper is lightly loaded, it might work.

    You're right -- with a "normal" motor (i.e. DC PM motor), you'd get a
    real light show at the commutator, and might smoke the drive. Steppers
    don't work that way, though. The worst that can probably happen is
    that the stepper will "lose step". That is, the torque will oppose the
    change in direction, and cause the stepper not to rotate to the right
    position. Usually you can hear this happen -- the stepper makes a
    fairly loud sound as it tries to hunt towards getting in step again.
    This is more of a problem as you go much past 1 rev./sec. or so, and
    becomes much more of a problem with the greater rotational torque a
    rotating load on the shaft presents. When you're unloaded or lightly
    loaded, the moment of inertia is basically just the motor itself.

    This also may put extra stress on any diodes in your circuit which are
    made to dissipate the inductive kick, but they should be OK. A good
    stepper driver can't be smoked that way.

    So if you're working at slow revs and your motor is lightly loaded, you
    might just want to go ahead and try it.

    Good luck
    Chris
     
  3. Hey guys,

    Just wondering, given the Chris's explanation of the inertia
    problem: if the lamp is fairly heavy, perhaps you could get
    less mass on the shaft by mounting the lamp on something else
    and just mounting a mirror on the shaft--aim the lamp at the
    mirror.




    Torben
     
  4. Eric R Snow

    Eric R Snow Guest

    I wonder if maybe a hobby servo might work for this. They are cheap,
    though not as cheap as surplus steppers, and many cheap and easy to
    build circuits can be found on the web to control them. Since they
    have position feedback the lost step problem is avoided. Another
    solution might be to go to a store and look at how a fan oscillates
    with only a mechanical linkage. Then the motor always turns the same
    way. This way a stepper could be used with the driving circuit
    controlled by a pot. Since you already have the stepper driver this
    might be cheapest. And stepper motors have higher torque at slower
    speeds.
    Good luck.
    ERS
     
  5. Jason S

    Jason S Guest

    Thanks for all the replies guys, I appreciate it.

    Just to give you an idea of what I was originally planning to do, I was
    thinking of using a small plastic case with a large LED bulb ... pretty
    lightweight really... the whole box would tilt at various angles by the use
    of a low RPM motor of some sort - thinking a stepping motor might do the
    job. I ran a couple of tests with one and found that it may fail on me at
    higher speeds.

    So I've been thinking about a Servo or Reversible Gearhead Motor. I've used
    neither of these before, but looking into how they work. They may very well
    be what I am looking for, as I am trying to avoid the use of mirrors and
    potential "slips" and freezes that may result from a stepping motor.

    Unless there are stronger stepping motors out there? haha

    Thanks again,

    Jason.
     
  6. Eric R Snow

    Eric R Snow Guest

    There are steppers that are plenty strong. You just need the driver.
    The nice thing about a hobby servo is that the feed back is built into
    it. You just need to provide the pulse train. The servo will keep
    trying to achieve position.
    ERS
     
  7. Rich Grise

    Rich Grise Guest

    "stronger"? How about 3.1V 4A, 300 in-oz holding torque? I've got one you
    can have for ten bucks. ;-)

    Cheers!
    Rich
     
  8. Jasen Betts

    Jasen Betts Guest

    should be OK as long as you don't overload the motor or the controller.

    Bye.
    Jasen
     
  9. Jason S

    Jason S Guest

    Yeh, the servo sounds pretty good actually. However I read somewhere that
    they spin at full speed when the angle they need to turn is close to max
    angle, e.g. 160 degrees, but not as fast for shorter distances/angles. Can
    the speed of these things be controlled? I wouldn't think so.

    Jase
     
  10. Jason S

    Jason S Guest

    shit, that sounds pretty powerful, haha.
    thanks for the offer Rich... I might get back to you on that. Haven't
    decided yet =)

    Jase.
     
  11. Don Bruder

    Don Bruder Guest

    shit, that sounds pretty powerful, haha.
    thanks for the offer Rich... I might get back to you on that. Haven't
    decided yet =)

    Jase.
    [/QUOTE]

    I seriously just might take him up on it if you don't. It DOES sound
    like a fairly powerful stepper, and that's what I'd like to use for the
    tilt on the camera pan-/tilt-head I'm trying to develop. (I've already
    got the pan part ready to go. Thanks, folks, but don't try to sell me a
    "pre-built" kit - I know that such animals already exist, but I'm doing
    it from the "scrounge-pile" purely for the sheer "Am I able to make it
    happen?" of it - call it a self-administered, self-graded "Final Exam"
    in computers/electronics/robotics/scavenging/MacGuyvering :) )

    A couple-few questions for Rich, though -
    1) I know an inch-ounce is the force the pivot will see if an ounce of
    weight (assuming we're at 1 earth gravity) is placed on a 1 inch lever.
    And a ft-lb is the force of a pound of weight working against a 1 foot
    lever. So can someone check me here? (300In/Oz) / 192 (12 inches to a
    foot times 16 ounces to a pound = 192In/Oz per ft/lb?) = about 1.6
    ft/lb? Or have I got the conversion hopelessly screwed up?

    2) Is this 300 in/oz/1.6 ft/lb measured directly on the motor shaft, or
    is this after a reduction package, and if reduction, is the geartrain a
    worm, pancake type, or maybe even a combination of both?

    3) How many phases (I'm assuming 4) and control wires? (Assuming 6) and
    are the phases tagged, or do I have to play "What happens if I energize
    in this sequence?" to find out?

    4) What's the step angle per phase?

    5) If it's supposed to be [email protected], got any suggestions for how I should
    expect it to behave if I were to try to power it from a [email protected] supply?
    How about [email protected]? (Besides the most intuitive "All the smoke will
    probably leak out - whether it leaks out of the PS or the stepper is
    questionable" scenario - IF there's a viable alternative - right now,
    those are the flavors of juice I can supply easily. Hmmm... brainstorm
    just hit: I've got multiples of that PS - Do SMPSes parallel OK? That'd
    give me [email protected] that I could mess with regulating down to 3.1V if I
    absolutely have to.)

    6) (And last - I think) What kind of physical dimensions and weight on
    this unit? Shaft size? Length? Splined, smooth, or geared? Gear or
    spline pitch/tooth count (if applicable)?

    7) (This is really last) How many do you have/want to get rid of?
     
  12. Eric R Snow

    Eric R Snow Guest

    I seriously just might take him up on it if you don't. It DOES sound
    like a fairly powerful stepper, and that's what I'd like to use for the
    tilt on the camera pan-/tilt-head I'm trying to develop. (I've already
    got the pan part ready to go. Thanks, folks, but don't try to sell me a
    "pre-built" kit - I know that such animals already exist, but I'm doing
    it from the "scrounge-pile" purely for the sheer "Am I able to make it
    happen?" of it - call it a self-administered, self-graded "Final Exam"
    in computers/electronics/robotics/scavenging/MacGuyvering :) )

    A couple-few questions for Rich, though -
    1) I know an inch-ounce is the force the pivot will see if an ounce of
    weight (assuming we're at 1 earth gravity) is placed on a 1 inch lever.
    And a ft-lb is the force of a pound of weight working against a 1 foot
    lever. So can someone check me here? (300In/Oz) / 192 (12 inches to a
    foot times 16 ounces to a pound = 192In/Oz per ft/lb?) = about 1.6
    ft/lb? Or have I got the conversion hopelessly screwed up?

    2) Is this 300 in/oz/1.6 ft/lb measured directly on the motor shaft, or
    is this after a reduction package, and if reduction, is the geartrain a
    worm, pancake type, or maybe even a combination of both?

    3) How many phases (I'm assuming 4) and control wires? (Assuming 6) and
    are the phases tagged, or do I have to play "What happens if I energize
    in this sequence?" to find out?

    4) What's the step angle per phase?

    5) If it's supposed to be [email protected], got any suggestions for how I should
    expect it to behave if I were to try to power it from a [email protected] supply?
    How about [email protected]? (Besides the most intuitive "All the smoke will
    probably leak out - whether it leaks out of the PS or the stepper is
    questionable" scenario - IF there's a viable alternative - right now,
    those are the flavors of juice I can supply easily. Hmmm... brainstorm
    just hit: I've got multiples of that PS - Do SMPSes parallel OK? That'd
    give me [email protected] that I could mess with regulating down to 3.1V if I
    absolutely have to.)

    6) (And last - I think) What kind of physical dimensions and weight on
    this unit? Shaft size? Length? Splined, smooth, or geared? Gear or
    spline pitch/tooth count (if applicable)?

    7) (This is really last) How many do you have/want to get rid of?[/QUOTE]
    Greetings Don,
    It's nice to be able to post something I actually know something
    about. I fiddled around with steppers a few years ago and actually
    built some metalworking stuff with them. If you want to make 'em spin
    faster the trick is to use higher voltage with resistors to limit the
    current. So go ahead and drive that 3.1 volt stepper at 12 volts but
    limit the current to 4 amps. SMPSes don't work well for these because
    they can destroy your controller. If your controller is robust enough
    then I suppose you could go that way, but I don't know enough about
    electronics and stepper driver chips to know for sure. When I tried to
    use a SMPS the voltage spikes destroyed the driver chip. The driver
    chip controlled transistors which controlled the stepper. The best
    power supply I made consisted of a surplus toroidal xmfr, a full wave
    rectifier, and a cap. I drove 5 volt rated steppers with 40 volts and
    used big resistors for current limiting. There are more than one type
    of stepper driving chip available. The ones I used took step and
    direction inputs and output the switching sequence. It was a cheap
    device. It did not have an idle current limiting feature though. This
    is important if you are driving the steppers at high current. The
    stepper can be driven at high current for speed and torque but when
    the stepper is idle this same current will overheat the motor. The
    best system I built was a kit from an outfit called CAMTRONICS. The
    guy who sold these kits is named Dan Mauch and is a good guy. If he
    still sells stepper driving kits they will be better than the one I
    bought from him because he is always trying to improve his products.
    Cheers,
    Eric R Snow,
    P.S. You want to avoid high voltage rated steppers. The highest
    stepping rates at the highest torque will come from driving the low
    voltage motors in the manner described above. And finally, it's been a
    few years since I messed with steppers so I may have given some
    erroneous info above.
     
  13. Wildepad

    Wildepad Guest

    I seriously just might take him up on it if you don't. It DOES sound
    like a fairly powerful stepper, and that's what I'd like to use for the
    tilt on the camera pan-/tilt-head I'm trying to develop. (I've already
    got the pan part ready to go. Thanks, folks, but don't try to sell me a
    "pre-built" kit - I know that such animals already exist, but I'm doing
    it from the "scrounge-pile" purely for the sheer "Am I able to make it
    happen?" of it - call it a self-administered, self-graded "Final Exam"
    in computers/electronics/robotics/scavenging/MacGuyvering :) )[/QUOTE]

    I built one using the steppers from old dot-matrix printers. My camera
    is fairly heavy (Sony Mavica MVC-FD7) but it moves smoothly.
    --
     
  14. Don Bruder

    Don Bruder Guest

    My application will be using a 555 to provide a clock signal for a
    bi-directional counter chip, which will be driving a one-of-four
    decoder, which will in turn be driving four optocouplers, each claiming
    to be good for switching up to 70 volts @ 2.5 amps on the output side,
    to drive the bases of four Darlingtons, each rated for 60 volts, 10 amps
    continuous/15 amps peak across the C-E junction. In other words, the
    "logic power" side is going to be completely isolated from the "high
    power" side of things, electrically speaking, and the high power side is
    over-engineered to the point of nearly ridiculous.

    The logic side should never, under any but the most incredibly unlikely
    batch of multiple "oops, shouldn't have done that" circumstances
    happening simultaneously (Any one of which would most likely destroy the
    whole thing anyway) see anything higher than TTL-logic level voltages.

    Considering how "beefy" the high power side of the controller is going
    to be, and the isolation provided by the optos (the datasheet claims
    between the high power and logic level sides, I don't foresee the PS
    being able to do much damage - Maybe, at worst, blow one or more of the
    Darlingtons, or in some *TRULY* bizarre combination of conditions nuke
    the optos, but not much else. Or am I completely naive?
     
  15. Rich Grise

    Rich Grise Guest

    I'm way too lazy to check your arithmetic here, and I can dismiss the
    rest of your questions with an "I have no idea". :)

    It'd pretty hefty - maybe five pounds or so; here are a couple of pix:
    http://www.abiengr.com/~sysop/images/Stepper1.jpg
    http://www.abiengr.com/~sysop/images/Stepper2.jpg
    http://www.abiengr.com/~sysop/images/StepperPlate.jpg

    The name plate kinda got taken upside down, but I've fixed that. :)
    No Idea - I presume at the shaft. That's where I'd measure it, anyway. :)
    I dunno - it's got nine wires, and I haven't ohmed any of them out - I
    guess I should... Crap. I can't find my little Micronta toy DVM, and
    the little VOM would just read continuity - would that help? Yeah, why
    not - it's another opportunity to go dig around my boxes...

    OK, here goes:

    W = White, V = Violet, Bk = Black, O = Orange, G = Green, Y = Yellow,
    R = Red:

    The wires are: Wh/V, Wh/O, Bk, O, G/Y, Y, R, W/Y, W/R. (that's body/stripe)

    So, to continuity:
    W/V | W/O | Bk | O | G/Y | Y | R | W/Y | W/R
    W/V - no yes no->
    W/O - yes no->
    Bk yes - no->
    O yes no->
    G/Y no no no no no no no no no Frame- yes

    Uh, oh - I see a pattern emerging here!

    Y - wh/y
    R - wh/r
    W/Y
    W/R.

    So it apparently has four independent coils, which are probably polarized
    by the stripe in the wires. :)
    It says, "200 steps per rev", so it'd just take some arithmetic,
    presumably.
    12V would burn up the windings, and 1.5A isn't enough to get it to step
    effectively under any practical load.
    I seriously doubt if SMPSs can be paralleled, unless they're designed to
    be ganged. They'll put each other into voltage limit or something - I
    hear it's really horrific =:-O .

    I'd try to find a supply that can do the 4 amps, and with some voltage
    compliance, like 6 or 12v, and drive the windings with a constant current
    sink.
    Hopefully, the pix cover this - here's some "actual" dims:
    shaft dia: .375
    Two flats, 90 degrees apart, .340 from flat to opposite side of shaft
    Mounting flange: 3.40" square, with a round 2.875 projection about .125
    tall;
    Mounting holes on a square, on 2.75" centers, diam. about .220

    The flatted end of the shaft is sticking out of the end with the flange,
    about 1", and there's about 1.25" of round shaft sticking out the other
    end, where the wires come out.
    Just the one - it's starting to sound like I should put this on ebay!

    Cheers!
    Rich
     
  16. Rich Grise

    Rich Grise Guest

    With a hobby servo (like in R/C airplanes), it's really easy to control
    the speed, up to a point. They get a position command from the receiver
    (or controller), that's a pulse train - I don't remember the exact
    figures, but it's fairly liesurely, like 20 ms at a few hertz. The pulse
    width tells the servo what position to go to *now*, so the speed would be
    limited by how fast the motor can turn. Of course, you can make it go as
    slowly as you want, by just commanding it to move a little bit at a time.

    The last time I worked with these things, there was also a "motor
    controller" available, where the PWM signal controlled the _speed_
    of an external motor, but they're dangerous - if you lose the signal
    in an R/C airplane, the servos freeze - if you lose the signal to the
    motor controller, it freezes _at whatever speed it was driving the
    motor before_. This is a helluva thing when your robot breaks itself
    at the demo of your new controller system in front of would-have-been
    customers. )-;

    Cheers!
    Rich
     
  17. Don Bruder

    Don Bruder Guest

    Yikes! That's definitely a hefty beast!
    Well, so would I, but I was trying to find out if it was geared, or
    direct. Looks to be direct - I don't see much available space for a
    geartrain in the unit. Nothing inherently WRONG with that concept, just
    sorta surprising for such a beefy stepper. The "big boys", torque-wise,
    seem to almost always be a "weakling" coupled to a heavy reduction
    geartrain of some sort.
    Sounds reasonable, with G/Y being a frame-ground.
    Good ol' 1.8/step, then. Fairly typical.
    I kinda figured that to be likely. Worth asking, though :)
    Really? Now doesn't THAT just about suck :( I've got what seems like
    about half a boatload of switchers laying around, many identical (pulls
    from old Apple IIes) that are just crying to be paralleled for high-amp
    Might end up powering the beast off a car battery/solar array charger
    type setup. Hard to say at this stage. The "development-so-far" has been
    done with one of the Apple IIe power supplies mentioned.
    Yep, pretty well.
    Do that, and you just priced me out of the game :( Can't blame ya if you
    do and it brings in a decent bundle, but at least for right now, I can't
    "run with the big dogs", money-wise. I'll let Jason have first crack at
    it, but do drop me a line (See my sig) if things don't work out there
    and you still want to part with it for cheap-ish.
     
  18. Jason S

    Jason S Guest


    haha, OMG, you ARE serious! Half the stuff I don't know what you're even
    talkin about! =)

    Jase
     
  19. Don Bruder

    Don Bruder Guest


    haha, OMG, you ARE serious! Half the stuff I don't know what you're even
    talkin about! =)

    Jase
    [/QUOTE]

    All but #1 and #7 are fairly important things to know about a stepper's
    capabilities, with #s 2, 3, 4, and 6 being the most critical for
    figuring out which one to use in your application.

    #2: Torque - 300 inch-pounds of holding torque means that it will keep
    300 ounces (A bit less than 19 pounds) of force from moving a lever one
    inch inch long, assuming the lever pivots on the stepper's shaft. A
    stepper with only 1 inch-ounce of holding torque isn't very strong at
    all, and will probably not be worth trying to use for turning anything
    heavy, or anything that needs tobe held to a tight positioning against
    some outside force acting on it, since a fart from across the room just
    might be enough to break its step. A "weak" stepper can, in effect, be
    made "stronger" by having it drive a reduction geartrain, so that the 1
    inch-ounce unit driving a 16:1 reduction could hold position against a
    pound of force being applied to that one inch lever, instead of an
    ounce. The tradeoff is, of course, speed - It's now going to take 16
    turns of the stepper shaft to get one turn of the output shaft of the
    geartrain, or 16 steps of the stepper to get one step worth of rotation
    at the output shaft of the reduction package. Worm-and-wheel, and
    "pancake" style gears are two construction methods for reduction units -
    Each has its plusses and minuses that are *WAY* off topic for an
    electronics newsgroup, and beyond my abilities to explain, besides.

    #3: Phases/control wires - Steppers come in various "flavors" - 2 and 4
    phase being most common, though others exist. Phase count influences #4
    (step angle) #2 (holding torque) and wiring - A two phase stepper
    probably has either 3 or 4 wires to connect, and wil have a difference
    stepping sequence than a 4 phase unit. 4 phase probably has 6 or 8 wires
    that need to be connected, and in both cases, one needs to know the
    stepping sequence to make the stepper do anything other than sit there
    and twitch spastically. Energizing one phase of a stepper results in it
    taking exactly one step. Energizing the next phase in the step sequence
    makes it take another step, etc, so to get it to turn, rather than
    wiggle, you repeatedly energize the phases in the step sequence.
    Figuring out the step sequence from a handful of wires and the info on
    the stepper's nameplate can be... "interesting". "So I need to step it
    as phase1, phase3, phase2, phase4 to get it to turn clockwise - OK,
    which pair of wires is phase1? Repeat for phases 2-4. Now did I get the
    polarity right? (IE, I've figured out that Black and Red are phase1, but
    if I put the juice to it as red(+) and black(-), it steps clockwise, and
    reversing the polarity makes it step counterclockwise)

    #4: Step angle: How far does the shaft turn for each step that happens?
    1.8 degrees per step is very common, but other angles are possible -
    I've encountered 180 degrees per step units, 3 degrees per step, etc -
    *LOTS* of possibilities. #3 (Phases) usually has a big impact. Smaller
    step angles usually mean higher holding torque (but not always) and more
    phases usually mean smaller step angles (but again, not always) Smaller
    step angles ALWAYS mean more positioning precision is possible.

    #5: Power requirements - Too much, and all the magic smoke leaks out of
    something (maybe the power supply, maybe the stepper, maybe parts in
    between) Too little, and the stepper doesn't do much of anything.
    There's a "happy medium" to be found for each one. The one Rich is
    talking about wants 3.1 volts at 4 amps. Volts and amps can be "fiddled
    with" in various ways to make it possible to apply more amps and less
    volts, or more volts and less amps, or some combination, to let you feed
    the beast with what you've got. But there are limits before the smoke
    leaks out.

    #6: Physical properties - "Will it fit where I want to put it? And if it
    will, can I get it mechanically connected to what I want it to drive?"
    It's more than a bit difficult to mate a round-with-a-flat shaft to a
    driven gear, ferinstance, and trying to fit a smooth round shaft to a
    splined input is probably going to work about as well as a lead balooon.

    Hope this helps... :)
     
  20. Tim Auton

    Tim Auton Guest

    The newer digital servos don't have the same limitations[1] as older
    analogue designs. They provide full torque for minimal displacements,
    programmable endpoints and probably other features I don't know about.
    I don't know if speed is controllable beyond slowly ramping the input.
    Search the web for 'digital servo' and you'll find Futaba, HiTec and
    others have a range. They aren't as cheap as regular servos, but they
    are pretty good.

    Tim

    [1] It's a limitation in normal servo operation, but when modified for
    continuous rotation that "limitation" facilitates (fairly crude) speed
    control using the original electronics.
     
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