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  • There are different motor types:
    • stepper: direct control but less powerfull, no feedback necessary
    • servo, DC, AC motors: need feedback & power modification (closed loop systems)
    The most easy way is a stepper motor which has the most simple drive system without feedback.

    For practicing I bought some small motors:
    Types:MOTS2 ST35MOTS1 ST28103H546 Sanyo Denki
    Rated voltage:12VDC12VDC3.15
    Angle/step:7.5 deg (?)5.625 deg (?)1.8
    Gear ratio:1:85 (?)1:64 (?)none
    detent torque:350gfcm (0.034Nm)310gfcm (0.030Nm)1.5 kgcm (0.15 Nm)
    pull-in torque:600gfcm (0.059Nm)360gfcm (0.035Nm)?
    max. starting pulse rate:500pps700pps500pps
    max. slewing pulse rate:800pps1400pps?
    max. speed:11.8 rpm20.5 rpm30 rpm
    steps/rev:2040 (tested!!)2048 (tested!!)200
    connector order:
  • B2: Blue
  • B1: Pink
  • A2: Yellow
  • A1: Orange
  • GND: Red
  • GND: Brown
  • B2: Blue
  • B1: Pink
  • A2: Yellow
  • A1: Orange
  • GND: Red
  • (1 Nm = 10 Kgcm = 100 Ncm = 8.85 Lb In = 141 oz in = 10197.16 gfcm)

    From the MOTS2 could be concluded that there are 2 pairs of coils (1 & 2) which both have an A & B connection, so this will be a unipolar winding, see picture:

    Propably the MOTS1 will have the same winding, but now brown & red are internal wired.

    It appears that current rise time is depend on the L/R constant (coil inductance/resistance). This means with the same power the motor will react faster. In graph below the formula is shown and the current rise against time.

    So it's obvious to have a low L/R constant for better results. Motors I found so far have a L/R between 2 and 10 [mH/ohm].

    Lowering L/R Constant:
    By adding an extra resitance, the L/R could be lowered and the voltage could go up, so the current rise time will react faster. So your motor could run faster at higher step frequencies. Because torque is lineair to current, you have more torque left at same speed :)

    When you buy a stepper, sometimes you have more winding options, see picture below.

    Connection:Graph: Resistance: Inductance: Current: voltage: Holding Torque:
    Unipolar 2 & 4 Nameplate Nameplate Nameplate Nameplate Nameplate
    Bipolar Series 3 & 5 X2 X4 X0.707 X1.414 X1.414
    Bipolar Half Coil 1 Nameplate Nameplate Nameplate Nameplate Nameplate
    Bipolar Parallel 6 X0.5 Nameplate X1.414 X0.707 X1.414

    This will result in different torque-speed outputs and is also depending on the type of driver you use. See picture below for some different winding methods:

    The most simple drivers will have 4 inputs somekind of converter to higher voltage and 4 outputs towards the coils of the (unipolar) stepper. If connected to the LPT some kind of isolation to the low power side is needed. There are 3 isolation possibilities:
    • No isolation, direct transistor driven, potentially damaging to computer
    • Optical isloation, safe up to 1500~3000V
    • Buffer/driver isolation, like the 7407 or ULN2803
    The circuit could look like one of the following:

    You need power for motors and steering power for ic's if used. I bought a PC power supply, because my motors need 12V and ic's need 5V. I found some good sites to modify the ATX power supply, goto: Desktop Power Supply from a PC or (Dutch article). I haven't modified my power supply yet, I'm using my running PC right now...