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Calculating Torque from motor specs

  1. Nov 6, 2009 #1
    Greetings folks. I am unsure how to calculate the torque produced by a motor if the known voltage input and amps are known. Here are the specs:

    3300 RPM @ 1.5Vdc @ 0.075 Amps. 6900 RPM @ 3VDC @ 0.095 Amps. 0.93" Diameter x 1.5" Long body. Operating Range 1.5 to 4.5 VDC. Shaft: 0.07" Diameter x 0.28" Long.

    What is(are) the equation(s) to calculate torque with the known variables given?
     
  2. jcsd
  3. Nov 6, 2009 #2
    From the current and voltage you can calculate the input power assume an efficiancy (80% ?) you know the speed so you can calculate the torque.
     
  4. Nov 6, 2009 #3
    I do not know me what good power or speed do me. What equation would I use to calculate torque? I do not know the relationships. It has been quite some time since a physics course.
     
  5. Nov 6, 2009 #4
    To get power output (watts), multiply current x volts x 80%
    To get torque in Newton-meters, multiply power by 60, and divide by 2 pi RPM = 6.28 RPM.
    Be sure you are using full-load volts, amps, and RPM

    Bob S
     
  6. Nov 6, 2009 #5
    So, going along with what has been provided...

    P(output) = Amps x Volts x 0.8
    P(output) = 0.075 Amps * 1.5 volts * 0.8 = 0.09 Watts
    Where P = Power

    T = (P*60)/(2*pi*RPM)
    T = (0.09 Watts * 60) / (6.28*3300 RPM * (1 min / 60 sec)) = 5.4 / 69.08 = 0.0762 N*M

    As for the information you gave me, when dividing by RPM, if a Watt is (1 Joule / second), doesn't Rotations Per Minute (RPM) need to be converted to Rotations Per Second? That would account for (1 min / 60 sec).

    I am not too familiar working with torque values, so would you say this could turn a wheel to move 5lb?
     
  7. Nov 6, 2009 #6
    Torque (Newton-meters) = Power (watts) divided by angular velocity (radians per second)

    radians per second = 2 pi RPM/60

    to lift 5 pounds with torque = 0.0762 N, 5 pounds= ~22 Newtons, so arm length r = 0.0762 N-m/22 N = 0.00346 meters
     
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