Calculating braking force for a disc

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Discussion Overview

The discussion revolves around calculating the braking force required for a rotating disc system, specifically in the context of selecting an OEM brake for a turntable driven by a direct drive motor. Participants explore the necessary torque calculations and the implications of motor de-energization on braking performance.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant proposes using the formula Torque = moment of inertia x angular speed to calculate the required torque for braking, resulting in a value of 112.85 Nm.
  • Another participant corrects the initial formula, stating that torque should be calculated using T = I α, emphasizing that α represents angular acceleration, not angular velocity.
  • It is noted that if the disc is rotating at a constant speed, the torque required is primarily to overcome friction, rather than to change angular velocity.
  • Participants discuss the need for additional information about the braking system and the specific conditions under which the brakes will be applied.
  • A participant mentions that the system consists of a direct drive motor and expresses the intention to install brakes that engage upon power cut-off.
  • There is a suggestion to use the motor itself for braking, but another participant clarifies that they want to de-energize the motor and apply brakes to test a specific condition.
  • Questions arise regarding the type of motor and whether it can be replaced or modified to facilitate braking.
  • One participant requests a clear sketch of the system with basic dimensions for better understanding.

Areas of Agreement / Disagreement

Participants generally disagree on the correct approach to calculating the required braking torque, with differing views on the implications of motor de-energization and the role of the motor in the braking process. The discussion remains unresolved regarding the best method for achieving the desired braking effect.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the braking system, the definitions of terms used, and the specific conditions under which the braking is to occur. The calculations and recommendations are contingent upon these factors.

Shady99
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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
 
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Shady99 said:
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

Your formula is incorrect.

T = I α

where,

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.
 
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SteamKing said:
Your formula is incorrect.

T = I α

where,

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.
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 doesn't 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
 
Use the motor for braking .
 
I want to de energise the motor and apply brakes to test a specific condition
 
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?

BoB
 
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
 
So this is a fail-safe mechanism?

BoB
 
Well this is an experiment 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
 
  • #10
Post a clear sketch of what you have with basic dimensions .
 

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