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Motor Speed Controller for 12v Brushed DC Motor (not PM) with speed regulation

Discussion in 'Electrical Engineering' started by Richard, Jan 19, 2009.

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  1. Richard

    Richard Guest

    I have a 12v Brushed DC motor (not Permanent Magnet) that takes about 2.5A
    when heavily loaded.

    I want to make (or buy a kit) that will drive the motor smoothly at slow
    speeds, and more or less maintain rpm under load. Also bi-directional.

    My input supply range is up to 20V DC at up to 5A.

    I think I may need a PWM controller. Preferably *not* based on a micro

    A speed controller allowing speed regulation seems to be the difficult bit
    when searcing for a suitable device, circuit or kit.

    Any motor experts here that knows what I can buy that would do the job?

  2. Phil Allison

    Phil Allison Guest


    ** The solution to your problem is very simple.

    Ditch the fucking pile of shit you have and get a suitable permanent magnet

    You stupid PITA wanker.

    ...... Phil
  3. Richard

    Richard Guest

    Well, I am just "messing about" with an old non PM motor that I have and it
    could be that seeking some speed regulation might be prohibitively
    expensive - considering I am just messing about.

    When it comes to stupidity, I think you will be your own accuser of being
    that one day.
  4. Richard

    Richard Guest

    I'm just messing with an old motor. It's series wound. Would it be easier,
    especially to get speed regulation, if I seperatedly energised the field
  5. Palindrome

    Palindrome Guest
  6. Richard

    Richard Guest

  7. Palindrome

    Palindrome Guest

    Well, yes, a closed loop controller will (generally) be more "difficult"
    than an open-loop one.

    The circuit in the reference provided is fairly easy to modify to allow
    for proportional control. The demanded speed is available as an analogue
    voltage. It should be fairly easy to produce an analogue voltage
    dependent on actual speed. Using the difference as the input to the PWM
    waveform generator will give you proportional control.

    You can then complicate things, say to reduce overshoot, as needed. Half
    a dozen op amps, in total, should do it nicely.

    However, you really need to have a very good reason for going for an
    analogue electronics solution, for a problem that lends itself so well
    to a digital one. I don't know what you have against micro controllers..
  8. Richard

    Richard Guest

    I'm on a learning curve here, because I'm not an electronic engineer.

    I've learned (AN905) that you cannot achieve precise speed control with
    series wound brushed DC motors. This is the type of motor that I have.

    I believe that I'd have to seperately excite the field windings of my motor
    to make the motor somewhat equivalent to a PM DC motor.

    I don't have anything against micro controllers. I was thinking things might
    be unecessarily complex if I used one. But, as I say, I'm not an electronic
  9. Palindrome

    Palindrome Guest

    One of the advantages of a microcontroller solution is that you can
    design-in much more complex control algorithms than is practical using
    analogue electronics. For the experimental, non electronics engineer,
    digital has many advantages - not least being the ease with which you
    can change timing constants or even the entire control system without
    touching the hardware at all.

    Speed control is a *control engineering* problem - not an electronics
    one. The solutions tend to involve lots and lots of mathematics. Which
    computers, eg microcontrollers, are good at.
  10. Phil Allison

    Phil Allison Guest

  11. Phil Allison

    Phil Allison Guest


    ** Bin it - you are wasting your and our time.

    Piss head.

    ....... Phil
  12. Palindrome

    Palindrome Guest

    It will probably "do the job" for his motor, once the connection changes
    needed to allow it to be made bi-directional have been done and the
    field winding has been adequately catered for. The OP is experimenting
    with speed control, not trying to meet a particular detailed
    specification (IIUC).

    What the brush gear will make of operating in the reverse direction to
    that for which it was designed is also a factor - but again, the OP is
    only experimenting.
  13. Phil Allison

    Phil Allison Guest


    ** Got any advice for turning sows ears into silk purses ???

    Maybe you can write us some code for it ?

    ** I see your forte is instructing wankers in the art of wanking.

    Bet you think that is doing a public service.

    Wot an imbecile.

    ...... Phil

    Remove motor. Remove throttle actuator hand grip device. Remove Power
    Switch. Remove charging connector. Remove battery pack. Remove motor
    controller. Remove drive train segments.


    Adapt and install drive train segments. Adapt and attach motor
    securely. Mount motor controller. Mount battery pack. Mount Charging
    connector. Mount Power Switch. Attach throttle actuator hand grip

    Drive away. 12 mile range... more if you assist. Convert a bike.
  15. Richard

    Richard Guest

    Okay, but is it not the case that I'd have to change speed using commands
    from my PC?

    But can I use a micro controller that stands alone, where I can set speed
    with a potentiometer?
  16. Palindrome

    Palindrome Guest

    Richard wrote:
    Not necessarily, see below.
    In the example that you chose above, an MCP6526 is used to convert the
    motor current and motor speed analogue inputs and present them to the
    PIC. The MCP6526 has 4 unused analogue inputs - one of which could
    connected to the wiper of your speed setting potentiometer.

    Alternatively, many PICs have built-in A/D converters, so don't need a
    device like the MCP6526 at all.

    But, why use a pot? They make sense when used with analogue electronics,
    of course. But, with a digital system, you can use BCD switches,
    "up/down" buttons + a digital display, etc..
  17. Rich

    Rich Guest

    I agree.

    There are at least 3 options:

    1 Analogue using pot or "up/down" buttons.

    2 Digital, control only thru PC.

    3 Digital using pot or "up/down" buttons.

    Either 1 or 3 would do. Perhaps 3 would be the choice of most.

    Actually having a rpm readout would be fantastic. Yes, I'd like that.

    But, I've not yet found a kit or a diagram to realise say option 1 or 3.
    Kits about but hard to find ones with speed regulation. And how many offer
    rpm readout.

    What I'd like ought to be piece of cake with all these sophisticated IC's,
    but I am out of my depth unless I find a kit or a product.

    I percieve that perhaps were in the realm of speed conntroller kit
  18. Richard

    Richard Guest

    I said:

    Tachometer can be a seperate project. No need to be part of the speed

    If I did not want speed regulation, it's just a matter of sourcing a kit.
    But it seems to me that once speed regulation is required there just ain't
    any kits about. But, perhaps some kits are capable of mofification to cater
    for speed regulation. But as a techical ecercise that's beyond me.

    So, I look for speed controller circuits that incorporate speed regulation.
    But I don't want to control speed from my PC.
  19. Richard

    Richard Guest

    My enquiry is perhaps more suited to a model makers or a robotics person. It
    needs someome who actually has hands on experience or is is familiar with
    making speed controllers. Someone with the hardware in posession.

    Thanks for the help anyway. Rich
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