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How Can A High-Torque Motor Have Low a low RPM

  1. Jan 9, 2013 #1
    Torque is the rotational force.
    If there is more force, how can the motor be slow?

    I'm building a DC motor and read that given a constant amount of coil, creating a very dense coil will increase torque but lower RPMs.
    Conversely, making it looser (bigger radius) increases RPM but lowers torque.
  2. jcsd
  3. Jan 9, 2013 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    The torque gives you acceleration - but it is possible to accelerate to any speed... however slow.

    For your motor - it will accelerate to a constant speed due to losses that are proportional to speed. This will be proportional to the amount of mass that has to be spun - and so is the torque.
  4. Jan 9, 2013 #3


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    The increase in torque at lower rpm is offset by increase in back emf at higher rpm, which decreases the torque at higher rpm.
  5. Jan 10, 2013 #4


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    Staff: Mentor

    Motors are connected to loads. The load determines the ratio between RPM and torque. If a "high torque" motor is not connected to a load and is just allowed to freewheel, it does not produce any torque.
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