driving dc motor???

Discussion in 'General Electronics Chat' started by amd_san, Dec 22, 2009.

  1. amd_san

    Thread Starter New Member

    Dec 21, 2009
    3
    0
    I have a voice controlled wheelchair project and i've questions:

    (1) what's the main purpose of H-bridge???is there any replacements????

    (2) for PWM speed control how can it be connected to the motor?it's function??

    for the mechanical part
    (3) are there any problems using 2 dc motors ???

    (4) what about servo motor for this application???

    any suggestions , links.

    thnx in advance
     
  2. eng1ne

    Member

    Dec 4, 2009
    97
    3
    1) Google 'h bridge' and read.

    2) Choose your motor first. PWM controls the speed as I think you understand.

    3) I don't see why not.

    4) See answer 3).

    Is this a personal project or an education related one?

    You have not given enough information. An hour of your research and reading will give you a much greater understanding than an hours worth of mine and other members time writing a response.

    I would suggest more reading. When you have a better understanding, return with more specific questions.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    It provides the ability to operate a DC motor in the forward and reverse directions without resorting to using DPDT relays or switches. Many integrated H-bridges also have inputs for PWM as well as direction.

    Relays and/or switches, which would be bulky and have a relatively short service life.

    It's connected to the H-bridge. The H-bridge controls the current flow to the motor.

    PWM provides an efficient means to control the speed of a DC motor. The old fashioned way was to use large power resistors, which consumed quite a bit of power and dissipated it as heat.

    Synchronization of the motor speeds might be a problem. Simply providing the same PWM signal to both motors would not guarantee that they were running the same speed, as the load on each motor will most likely vary constantly.
    That could be done, as servo motors would slave to the rotational position they were instructed to move to.

    A couple of H-bridges to look at:
    VNH2SP30 - Automotive Fully Integrated H-Bridge Motor Driver
    ZXMHC3F381N8 - 30v 3.3A SO8 Compementary enhanced MOSFET H-bridge
     
  4. amd_san

    Thread Starter New Member

    Dec 21, 2009
    3
    0
    its an education related one
    yes u r right, i'm reading rite now and alot of things become cleared to me

    another question :D
    do u have any idea how to turn the wheelchair right or left????
     
  5. amd_san

    Thread Starter New Member

    Dec 21, 2009
    3
    0
    SgtWookie thnk u very very very much :D

    (1) how can i overcome the Synchronization problem ????
    (2) if i will use a single motor how can i turn the chair rite or left????
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Please try to use proper English. People tend to not take you seriously here if you are using "texting" abbreviations.

    If you are using two motors, you could:
    1) Decrease the speed of one motor, keeping the other constant.
    2) Decrease the speed of one motor, and increase the speed of the other motor.
    3) Increase the speed of one motor, keeping the other constant.

    It is generally preferred to slow down as one turns, so the 1st option would likely be the best.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    You would need some kind of feedback from the wheels or motors.
    Research:
    Rotational Encoders
    Optointerruptors
    Hall-effect sensors
    These three methods are in common use. There are others, but these will be good for starters.

    If you used a single motor, you would probably need a differential to drive both main (tractive) wheels evenly, and some sort of servo arrangement to steer the front or rear wheels.
     
  8. eng1ne

    Member

    Dec 4, 2009
    97
    3
    Is the project goal to actually build the wheelchair?

    What is your part in the project; is it just yours? What sort of background do you have in engineering? Are you responsible for the voice controller?

    In answer to your question however, I can't think of any other practical solution better than SgtWookies in using two.

    To have only motor directly driving the wheels, a servo motor could be used to turn the axis of the wheels.

    But as SgtWookie said, two motors are generally desirable; I agree.
     
  9. eng1ne

    Member

    Dec 4, 2009
    97
    3
    Just posted as you did Sgt, apologies!
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,170
    395
    My electric tractor[ wheel chair guts] has two ,250W , 23V motors, using 2 slide pots for PWM, 0-100% control and toggle sws for forward/rev.A real bear to ride- noseat, just a few bruses. Chesp ones use one motor. one wheel drive, tiller front wheel for direction, my favorite is one motor with differential & front wheel steering.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    From your E-mail:
    Yes; many microcontrollers have hardware PWM capability; some are specifically designed for motor control.

    It depends on how well you can define your application, and how well you do in selecting the microcontroller to be used.

    The application will dictate which uC needs to be used.

    You need to define all of the requirements of the application first. This part will require lots of thinking and research.

    Then look at what is available in the way of microcontrollers that may be suitable for your project.

    You are a long ways away from performing the actual programming of the microcontroller; as you haven't completely defined the requirements yet.

    Either a capable diode, or perhaps a synchronously switched MOSFET used as an "ideal diode".

    You must carefully research the problem, and specify components that are suitably rated for the task at hand.

    But first, you must define the requirements.

    You will need to figure out what your requirements are first, and then see which motor or motors meet your requirements. The motor selection will dictate the batteries that you will use.

    I don't help people via E-mail, as it defeats the purpose of the Forums (sharing knowledge), along with depriving you of other knowledgeable input.

    Besides, it jams up my E-mail inbox. Believe it or not, I get a lot of E-mail requests for help. I refer them all back to posting in the Forum.
     
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