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DC Gear Motor

Discussion in 'Electronic Basics' started by Nikyu, Jan 6, 2006.

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  1. Nikyu

    Nikyu Guest

    I've got a pretty simple question about DC gear motors. I understand
    the relationship between torque, motor speed and Hp. Typically when I
    see a spec for a motor it list all three values. Are the torque and
    speed both attainable at the same time or are those the peak values?
    Because when I try to calculate the Hp from the listed torque and
    speed, I never the Hp listed.

    If I wanted a dc motor to have a torque of 2 ft-lb and a speed of 60
    rpm, then the motor would have to be able to put out 0.023 Hp.
    Correct?

    But as the speed is reduced, the motor can supply much more torque and
    like wise as the speed in increased, the motor cannot supply as much
    torque.

    Is my understanding correct?

    Thanks!
     
  2. Often, the HP listed is the motor shaft output, not the gear box output.
    Let me check. The torque of 2 ft-lb refers to the ability of the
    gearbox to produce a force of 2 pounds at a distance 1 foot from the
    axle. But one turn of that axle will pull that 2 pounds through a
    distance of 2*pi*1ft=6.28 linear feet. So the work done by the 2
    pound force per rotation will be 6.28*2=12.57 ft-lb of work. Multiply
    that by 60 rotations per second and you get 754 ft*lb/min or about
    ..023 of a horse power (1 HP=33,000 ft*lb/min). Check.
    Sounds pretty good to me. A DC (permanent magnet) motor has some zero
    load speed at a given supply voltage, and that speed falls pretty
    linearly to zero at stall torque. The peak horsepower usually occurs
    at about half no load speed (half of stall torque and half of no load
    speed).
     
  3. Jasen Betts

    Jasen Betts Guest

    yes.

    it's probably best to look at the data sheet which will give all the
    details, rather than relying a summary from a catalogue.

    Bye.
    Jasen
     
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