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I am trying to select a motor for a high-speed application where I need to rotate a load bearing cylindrical disc at 20,000 rpm. The total mass of the disc along with its load is approximately 1.5 - 2 kg. I'm attaching a diagram of my application along with this question. Kindly help me define the motor torque parameters for this application. enter image description here

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  • \$\begingroup\$ How long do you want to wait before you get to 20000 rpm? You need to dimension the masses better to compute the moment of inertia of the rotor. \$\endgroup\$ – D Duck Sep 20 '18 at 20:10
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    \$\begingroup\$ No torque is required if friction is zero. The torque you required depends on the acceleration you require and the friction. You need to specify these, your moment of intertia and your friction. \$\endgroup\$ – Transistor Sep 20 '18 at 20:12
  • \$\begingroup\$ This is mostly a mechanical engineering question. The disk is apparently 50mm in diameter. That is rather small disc for a mass of 0.5 kg. If it is made of pure osmium, it would be 10.14 mm thick. At 20,000 RPM, there will probably be significant aerodynamic drag. That in combination with the required acceleration torque will determine the required motor torque. If the motor is vertical as shown, the motor bearings need to be rated for the downward force due the the mass of the load plus the pass not the motor rotor. \$\endgroup\$ – Charles Cowie Sep 20 '18 at 22:34
  • \$\begingroup\$ Each of the two loads attached to the disc can not possibly have the same mass as the disc if the drawing is at all close to being to scale. To make any kind of estimate of the inertia and aerodynamic drag, something close to an accurate scale drawing will be needed. \$\endgroup\$ – Charles Cowie Sep 21 '18 at 14:13
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I guesstimating that you will need around .4Nm of torque for this (around .3 ft-lbs) and at 20,000RPM is going to be almost 1kW. That's somewhat high for a direct drive motor moving a 2kg load in my opinion. A "universal" motor (those found in things like blenders and routers) can get to those speeds, but are not likely available in big enough sizes to spin something that big. You will probably be looking at something very expensive like a 2 pole AC "spindle motor" driven by a VFD operating at 333Hz. So yu are looking at roughly speaking, $1000 US. Is that in your budget? the point being, you might want to consider using some means of mechanical speed increase so as to use a more standard low cost motor that will run at around 3000RPM.

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