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Calculating torque within a DC MOTOR?

  1. Jul 6, 2012 #1
    The torque that is generated inside a magnetic motor is caused from the magnetic forces that is this formula:

    F = ILB

    F: Magnetic force(Not sure what the unit would be...)
    I: Current(A)
    L: Torque(N.m)
    B: Magnetic field.( Gauss or Tesla?)

    I just need some help in calculating the total magnetic force I know the current & the magnetic field(measured in Tesla or Gauss in this cause?). However, the Torque is confusing for me to calculate... I've looked around and read theses slide countlessly but I really don't know how? I end up scratching my head all night wondering how to calculate the torque!

    Thanks in advance!
  2. jcsd
  3. Jul 6, 2012 #2


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    Staff: Mentor

    Hi Momento. Suggest recheck your textbook (or the web) again to establish what that "L" quantity is.
  4. Jul 6, 2012 #3
    My understanding is such that:

    F = I l B (sin Θ = 1 )

    where F = newtons, I = amps, l = conductor length, and B = magnetic field strength in Tesla.
    (remnant field strength may be .7 * max stated value)

    You could also use a motor 'constant':

    where torque in Nm/A = K * I, and BEMF = Kω

    such that K = 2NBLR

    where N = # of turns, B = Br*t/(t+g), L = active length (of stator), R = effective radius

    where Br = remanent flux density, t = magnet thickness, and g = air gap
  5. Jul 6, 2012 #4

    I'll give it a look.

    "(remnant field strength may be .7 * max stated value)"?

    All the rest is really confusing... Could you simplify it more and more...?
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