Calculating Torque for Rotating Disk: Specs, Friction, and Weight Considerations

[jayant C]

Hi all,
I am trying to calculate the torque required by the motor to rotate a disk at a constant speed. Specs are as follows:
1. Disk radius =80mm
2. Disk Thickness =2 mm
3. Disk Weight =50gm
4. Constant speed= 3000rpm(CONSTANT)
5. Motor friction torque= 1mNm
6. Disk position parallel to ground.My question are as following:
1 Other than motor friction torque what are the other torque to be considered to calculate the total torque required to maintain the constant speed?
2. Dose the weight of the disk come in picture to calculate the torque? if yes what is the equation?

If possible please provide the equations.

 

[Nugatory]

1 Other than motor friction torque what are the other torque to be considered to calculate the total torque required to maintain the constant speed?

There's air resistance around the moving disk, friction in the bearings, and a host of others. You'll have to decide for yourself which of these are negligible or are already counted in the "motor friction"

2. Dose the weight of the disk come in picture to calculate the torque?

In an idealized situation, only to the extent that it affects the frictional torque. In the real world if the disk is too heavy bearings will fail, the motor will stall, stuff will break or otherwise stop behaving according to the simple idealized equations.