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Calculating braking force for a disc

  1. Sep 21, 2015 #1
    Hello everyone,i am new here.

    I have a basic design problem that i am not confident about and require help.

    I have a disc with components on it and the disc is rotating with angular speed of 35 deg/sec(0.61 rad/sec).The moment of inertia of my disc+ component assembly is 185 kgm2.

    I have to select an OEM brake for the system. As far as i know, the torque required to select the brake can be found by the formula i.e. Torque=moment of inertia x angular speed,which comes out to be 112.85 Nm . Is it the correct way to solve my problem .Please help. Thankyou
  2. jcsd
  3. Sep 21, 2015 #2


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    Your formula is incorrect.

    T = I α


    T = torque, N-m
    I = mass moment of inertia for the disk, kg-m2
    α = angular acceleration (not angular velocity), in rad/s2

    This formula calculates only the torque required to change the angular velocity of the disk. If the disk is rotating at a constant angular velocity, then the only torque input required is that to overcome friction in the bearings, for example.

    IIRC, most brakes are designed according to the energy which must be dissipated in stopping whatever mechanism they are attached to.

    Your rotor is turning at less than 6 RPM, based on an angular velocity of 35°/s, which seems pretty slow. It's hard to advise further without knowing what you are trying to stop with the brake.

    I would recommend that you consult with a sales engineer at the particular brake manufacturer for more guidance in selecting the proper brake.
  4. Sep 21, 2015 #3

    thankyou for reply.......Actually my system is a turntable.....my system consists of a direct drive motor that is driving a shaft connected to disc,the disc has certain modules on it.....now the problem is that the direct drive doesnt have brakes, so i plan to install a brake to stop the motion once i power off the motor......the maximum system speed is 35 deg/ sec and the acceleration is 10 deg/sec2......now when the system is moving with 35deg/sec, i want to cut off the motor power and apply the brakes to stop the system.....whats your take on this...please help
  5. Sep 21, 2015 #4


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    Use the motor for braking .
  6. Sep 21, 2015 #5
    I want to de energise the motor and apply brakes to test a specific condition
  7. Sep 23, 2015 #6


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    What kind of motor is it? Depending on the type you can make the motor into a brake easily.

    Can you replace the motor or add another one?

  8. Sep 23, 2015 #7
    Motor is a direct drive servo motor......i can add a motor but its will not serve the purpose......i want to apply brakes when i de energise the motor.....i mean when i cut system power off then the brakes should engage
  9. Sep 23, 2015 #8


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    So this is a fail-safe mechanism?

  10. Sep 23, 2015 #9
    Well this is an experiemnt i want to perform.....i want to bring the system speed to 35 deg/sec and then turn off system power off.....now as i wud put those brakes tht engage on power cut off so my system will stop
  11. Sep 23, 2015 #10


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    Post a clear sketch of what you have with basic dimensions .
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