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what should consider when design motor speed controller

Discussion in 'Sensors and Actuators' started by KUMARA SHP, Aug 14, 2014.

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  1. KUMARA SHP

    KUMARA SHP

    122
    4
    Aug 1, 2014
    I am going to design motor controller for my next robot
    I have two geared motor 12V DC & 120RPM
    motor is SCKJ MOTOR & has some number on it 25GA370 (may be model no)
    I can't find data sheet for that
    so, what should I take into the account to design motor controller
    I am going to use ARDIUNO broad for my robo
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Well what do you want the motor to do, you dont say. Forward ,backwards, brake? How do you want to control it? You dont say.
    Adam
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,250
    2,703
    Jan 21, 2010
    You can measure some important characteristics.

    Firstly allow it to run freely from 12V and measure the current. That will give you the absolute minimum current the motor will demand.

    Now measure it's DC resistance. Use this to determine the maximum current at 12V. This gives you the stall current and allows you to size your controller appropriately (because it should not expire if the motor stalls). Note that the stall current is also drawn briefly as the motor starts.

    The actual current you'll expect can only be determined by knowing the load on the motor. It will be somewhere between these two currents, but I don't know where in that range. The easiest way to find out is to mock up the device and see what current is required.

    If you're using PWM then you will need to switch these currents, so you may need to consider switching losses in your controller.

    And don't forget to protect your controller from the effects of switching an inductive load.
     
  4. KUMARA SHP

    KUMARA SHP

    122
    4
    Aug 1, 2014
    ok I got it , as I mentioned I am going to control speed by using arudino broad, I have seen some motor controllers they are expensive
    I will go though your way and design motor controller ,I will upload it to see you all
    thank for all
     
  5. KUMARA SHP

    KUMARA SHP

    122
    4
    Aug 1, 2014
    I measured the current though the motor for 9V
    when no load it about 20mA
    when I tied it from hand stop the rotation it took 500mA
    my choose is l293D ic to control the circuit
    what do you think about my choice
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,250
    2,703
    Jan 21, 2010
    It has a peak output of 2A per channel. Your motor has a stall current of 500mA. The L293D should be safe :)
     
  7. BobK

    BobK

    7,660
    1,675
    Jan 5, 2010
    The trouble with that chip is, that it loses between 1.2 and 1.8V on each side, so 2.4 to 3.6V total. A bridge made of 4 MOSFETs would cost less and perform better. I am starting a robot project next week, and I have chosen these:

    http://www.mouser.com/Search/Produc...7virtualkey62110000virtualkey621-DMG6602SVT-7

    It is an N and P in one package, so 2 of them will make a bridge that can handle up to 1.5A with a drop of 0.36V at max current. I got 100 of them for $12, because the price break was so good. The built in body diode is able to handle 1.5A, so I do not even need external diodes, just two of these and you have a full bridge, so 4 full bridges for a dollar!

    Bob
     
  8. KUMARA SHP

    KUMARA SHP

    122
    4
    Aug 1, 2014
    I have seen two circuits with capacitors & same without them
    are they necessary? FS2GGDIHANAVUOO.MEDIUM.jpg
     
  9. KUMARA SHP

    KUMARA SHP

    122
    4
    Aug 1, 2014
    they are for reduce the noise , but I have seen only in few designs
    many l293 circuits are without capacitors
    so, if I use capacitor that may give advantage or problems?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,250
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    Jan 21, 2010
    It's best to start with the datasheet and what they recommend.

    It is unlikely that adding the capacitors as shown will cause problems other than those associated with size or cost.
     
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