stepper motor in loc

Discussion in 'N / Z Scale Model Trains' started by takev, Sep 27, 2003.

  1. takev

    takev Member


    I was wondering if anyone ever tried to put a stepper motor in a N-scale locomotif.

    I think it would make it possible to let the train move very slowly and presisely.

    The only worry I have is with the noise.
    And ofcource getting all the electronics inside a N-scale train, although for test you could put it in a wagon behind it.

    Take Vos
  2. zeeglen

    zeeglen Member

    Thought the same, but never heard of it actually being done. You're right, it would make for very slow, precise movement. But I don't know if anyone makes a stepper small enough to fit, the few i've seen tend to have a large diameter to get the torque. It might be more worthwile for manufacturers to keep the motor as is and lower the gear ratio instead. We don't really need locos that do 150 smph at 12V. Plus with pulse drive the quality 5 pole motors and gears work nicely already.

    Still, it wouldn't hurt to mention it to a few manufacturers anyway. Who knows what might happen as a result?
  3. takev

    takev Member

    I have looked on the internet for stepper motors and I found these things.
    Big site about stepper motors in general and how to.
    This would actauly fit my small N-scale diesel loc. There is a 3-16Volt version of it, so you could run it directly from the DCC track power.
    I have no idea about how much torque 1.6mNm is ( But I think torque of stepper is higher then a normal motor of the same size.

    There is also a 8mm motor on that site, with a 5V version, but that may use more electronics to downconvert the voltage.

    Now, about the electronics, the prototype may be quite large, but may be housed in a car behind it or in a passenger/loc combination.

    So, I am thinking of a digital track system, such as DCC, so that it can supply a high voltage to the motor while moving very slow.

    first using a diode bridge, a voltage regulator and some caps, suplies the voltage to the CMOS electronics and to the motor. The mass (-) is connected to the mass of the DCC decoder (compared to the motor suply wires, I may need some help from a manufacturer).

    Then a 555 timer is set up to run the train at about 50% of high speed, and the voltage reference input is hooked up to the motor supply wires of a DCC decoder with diodes (maybe some caps if the output is not regulated, and a voltage divider 2 resistors).
    This will make the pulses from the timer change in frequence depending on the settings of the DCC decoder.

    Now, the clock pulse from the 555 timer drives a CMOS decimal counter (the one which will only turn on one wire at the time). It is wired such the the 5th output is hooked up to reset, so it will count from 1to4. The inc/dec input of this counter is hooked up to the front/back light output of the DCC decoder, which will make the counter run forward or backward.

    Now, depending on the strength of the output drivers of the counter you may run the motor directly on these four outputs or through some transistors.

    So, not that much electronics, and quite simple. And I think a surface mounted version could be as big as a N scale decoder.
    And the stepper would be really strong on slow speeds.

    Still, my first layout isn't finished yet (I got my first point glued down now). And I don't have the digital components yet. So it might take a few months before I'll experiment with this.

    I hope there will be some discussions here what the best design would be, and maybe someone would build such a thing, just to try it out.
  4. takev

    takev Member

    Ok, instead of a decimal stepper,
    the mc3479 drives the motor in the correct way.

    Which means 555 clock output is used as the clock input for the mc3479. the DCC front/reverse light output to the CW/CCW input of the mc3479. And maybe an extra DCC output for the full/half step input. So you can select high and slow speed mode.

    It seems the mc3479 likes 5 volt input, which we would get by suppling the 555 with 5 volts, with a 5 volt regulator (7805 I did electronics about 12 years ago, I might have forgotten the type numbers). The motor output of the DCC decoder also needs its voltage lowerd (it should not be higher then the 555 suply voltage)

    The motor suply input for the mc3479, may not have to be regulated, I don't know.
  5. takev

    takev Member


    I have made an electronic schema.
    I don't have all the values yet.

    Any comments would be welcome.

    Greetings from Amterdam,
    Take Vos
  6. takev

    takev Member

    sorry here is the schema

    Attached Files:

  7. SD90

    SD90 Active Member

    Ok, I'll ask the question, what is a stepper motor?
  8. takev

    takev Member

    Hello SD90,

    A stepper motor is used in high persision applications, such as robots, foto scanners, floppy drives.

    The axis can be rotated in a certain position, called a step. The motors I was talking about, to put inside a N scale train, has 20 steps, a single step turns the axis 18 degrees.

    It works by having a lot of electromagnets on the wall of the casing, and a permanent magnet on the axel (precisly as a normal motor does not). Then you just turn the correct electromagnet on and the axis wil turn to that electromagnet, then you turn on the neighbouring electromagnet, etc.

    In most motors electromagnets are grouped and controlled by four wires, when these four wires are used in the correct sequence the motor turns forward, or backward. You can even use some fancy electronics and half step the motor by turning on more electromagnets,
    this is less precise, but with smoother operation and less noise.

    Unlike normal motors the amount of voltage applied to the motor does not change the speed, it only changes how much torque it outputs. The speed of the motor is controled with how fast the sequence is run through (this is why there is so much electronics to convert the voltage from the DCC decoder to something a stepper motor needs).

    As these motors are brussless (there are no electromagnets on the axel). They are maintenans free, which is why they are used in space satelites.

    for model trains these motors would mean it is possible to make the train move so slowly that you won't hardly see it move. While still outputing anough torque to drag a lot of cars behind it. It may also mean that your wife would be complaining about the noise (ever heard a scanner?) and it may melt your locomotive, but we have to test these issues first.

    I hope this answeres your question. As I am away this week, without Internet (I think). I will answer follow up questions next weekend.

    Take Vos

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