Pwm help please, speed control + torque

Discussion in 'General Electronics Chat' started by Mikey1604, Jul 24, 2018.

  1. Mikey1604

    Thread Starter New Member

    Jul 24, 2018
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    0
    Hello everybody I just created this account as I'm struggling to resolve my questions myself, hopefully someone can help me with them

    Ok first of all this is the pwm I purchased
    https://m.ebay.co.uk/itm/6-30V-DC-M...M-Control-Forward-Reverse-switch/182003602041

    And this is the motor
    https://m.ebay.co.uk/itm/Large-Torq...Gear-Bearing-12-36V-555-DC-Motor/282951529686

    Power supply is either 2A plug or 10A battery (still waiting for delivery) both 12V

    Problem I am having is after connecting all together with the 2A plug as that's all I have at the moment is that there is extremely limited range on the potentiometer it goes from slow to very fast in about 1mm turn, I was wondering if I replaced the potentiometer with a different one would that give me more control on the speed? Also how would I calculate what potentiometer size I would need?

    But the second problem is more important again, at full speed the motor has lots of torque more than enough for my needs but when the speed is lowered there is litteraly no torque at all, I read online that with a pwm you could lower speed and keep the torque high? But having tried that I'm guessing that information was incorrect?
    Would a different pwm board help?

    Is there a way to lower speed and keep torque high? Other than a gearbox?

    Sorry for so many questions, I'd be very grateful for any help, mike
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    5,884
    To maintain torque you require some kind of feedback method in order to maintain torque required for a specified rpm.
    If your application only requires low rpm, a gearbox could be used.
    Max.
     
  3. Mikey1604

    Thread Starter New Member

    Jul 24, 2018
    3
    0
    Not exactly low rpm needed I would say 200rpm minimum going up to anything the motor can give, torque needed isn't a lot but at the moment it's so weak at lower speeds I could stop it by pressing lightly with a finger
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    18,840
    5,884
    With open loop PWM at very low rpm the torque (current) is very low, especially on a motor with high maximum rpm.
    A sensor on the output shaft using simple feedback can overcome this.
    Max.
     
  5. jpanhalt

    Expert

    Jan 18, 2008
    7,665
    1,870
    4QD is a valuable resource for getting started. Here is a link to its introductory page. San down to the paragraph below the image of pulses: http://www.4qdtec.com/pwm-01.html

    The motor you have has a minimum voltage of 12 volts, so at PWM's that give << 12V it will not run. Then when you get close to 12V (average) it will start to run and go to full speed rather quickly.

    Consider testing with a higher voltage supply and/or using a motor rated for say, 3 V to 12 V.
     
  6. Mikey1604

    Thread Starter New Member

    Jul 24, 2018
    3
    0
    Thanks for your replies I should have mentioned I am very inexperienced with electronics and only understand the very basics, would this be possible on the pwm board I'm using? And could you possibly link to the product? Thanks again
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    18,840
    5,884
    Typically it is done with some kind of Microprocessor.
    You don't necessarily need to go full PID loop, but simple speed correction is possible using say a 4 to 10 pulse sensor on the shaft.
    The PWM controller you have is open loop variety, unfortunately.
    Max.
     
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