simple math (but hard 4 me)

Discussion in 'Homework Help' started by isakiwanuka2013, May 13, 2013.

  1. isakiwanuka2013

    Thread Starter New Member

    May 12, 2013
    I have a thin disk that

    In weight is 30 Kg in total

    It is 0.5 meters in diameter

    So moment of inertia is = I = 0.25xMxR^2

    So I = 0.25x30x0.25^2 = 0.46875 kg-m^2

    i want to suggest a stepper motor to be brought with 4.5Nm

    my angular velocity is 0.6282 rad/sec

    so now i want to work out torque but have no idea???

    Torque of a Body in Angular Motion
    T = J α (2)


    J = polar moment of inertia (kg m2, lbm ft2)

    α = angular acceleration (rad/s2)

    but i have angular velocity

    i tink if i integrate velocity i get accelartion therefor rad/s ^2
  2. WBahn


    Mar 31, 2012
    What is the 4.5Nm for? Those are units of torque.

    The motor has to deliver power for two reasons: (1) to change the speed of the disk, hence you need to decide what the fastest acceleration you need is, and (2) to overcome the friction (and any other) losses, which you haven't even touched on.
  3. WBahn


    Mar 31, 2012
    Oh, and you integrate acceleration to get velocity. To get acceleration from velocity, you differentiate.