What is the required torque for a spinning flywheel?

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Discussion Overview

The discussion revolves around determining the torque required to start a spinning flywheel, including considerations of moment of inertia and angular acceleration. Participants also explore the implications of RPM in relation to acceleration and the necessary specifications for a slip ring induction motor.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant inquires about the torque needed when starting a flywheel, noting its weight and desired RPM.
  • Another participant states that the torque required is dependent on the moment of inertia and the desired rate of acceleration.
  • A participant references angular acceleration and provides a formula for calculating it based on changes in RPM over time.
  • There is a discussion about the distinction between RPM as a measure of speed and the need to consider angular acceleration for torque calculations.
  • Participants provide links to resources for calculating moment of inertia for various shapes, indicating that the method may vary based on the geometry of the flywheel.

Areas of Agreement / Disagreement

Participants generally agree that torque is influenced by moment of inertia and acceleration, but there is no consensus on the specific calculations or methods to determine these values. The discussion remains unresolved regarding the exact torque required and the best approach to calculate it.

Contextual Notes

Limitations include the need for specific details on the desired acceleration time and the complexity of the flywheel's shape, which may affect moment of inertia calculations.

Tjtech
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Hello, I would like to know the amount of torque required when the flywheel starts? I know that once at speed the flywheel doesn't require torque. I would also like to know what size of slip ring induction motor to run as the below mentioned speed.

The weight of the flywheel is= 6500 kg
( wt. shaft, flywheel boss and wall 2700 kg + mass 3800 kg = total 6500 kg )
RPM= 1550
Diameter=2200mm

Thanks for your help.
 
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The amount of torque required depends on its moment of inertia and how fast you want it to spin up.
 
9be08b9254aaacbc0386b26bf137f2ae.png

http://en.wikipedia.org/wiki/Angular_acceleration#Equations_of_motion
 
Last edited by a moderator:
...and angular acceleration alpha is approximately closely enough by delta angular velocity / delta time.
 
russ_watters said:
The amount of torque required depends on its moment of inertia and how fast you want it to spin up.
Thanks russ_watters, isn't how fast I want the fly wheel to spin the RPM? And if you don't mind how am I supposed to calculate the moment of inertia? Sorry for the trouble as am still an amateur at this thanks
 
Tjtech said:
Thanks russ_watters, isn't how fast I want the fly wheel to spin the RPM? And if you don't mind how am I supposed to calculate the moment of inertia? Sorry for the trouble as am still an amateur at this thanks
By RPM we usually mean the speed of rotation after the flywheel is up to speed. russ_watters and the other posters are talking about acceleration. How long do you want it to take to go from 0 RPM to max RPM? The shorter the time, the more torque you'll need.

You can find the moment of inertia on this table: http://en.wikipedia.org/wiki/List_of_moments_of_inertia
Note that multiple values are listed for each shape. The subscript tells you which axis you are rotating about.
 
Tjtech said:
Thanks russ_watters, isn't how fast I want the fly wheel to spin the RPM?

No, it's the angular accelration α that I mentioned in my post. As tygerdawg mentioned, the average angular acceleration is αavg = ( RPMfinal - RPMinitial ) / time.

Tjtech said:
And if you don't mind how am I supposed to calculate the moment of inertia? Sorry for the trouble as am still an amateur at this thanks

This the I in the equation of my previous post.

If it is a solid disc:
170px-Moment_of_inertia_solid_cylinder.svg.png
29bac02573ea5d0bbf08a7506e4e9b37.png


If it is a ring:
185px-Moment_of_inertia_thick_cylinder_h.svg.png
bb27a6644113c6a25f841acabb3a003e.png


For other basic shapes: http://en.wikipedia.org/wiki/List_of_moments_of_inertia

Calculation method for more complex shapes: http://en.wikipedia.org/wiki/Moment_of_inertia#Calculating_moment_of_inertia_about_an_axis
 
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