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Thread: How to calculate the torque that a flywheel will deliver.

  1. #1
    Associate Engineer
    Join Date
    Dec 2015

    How to calculate the torque that a flywheel will deliver.

    I do not have formal education in engineering, but I enjoy designing and engineering things, and I have applied a some formulae for stationary things.

    I am trying to understand the computations about flywheels and torque.

    After building a small prototype and learning some things, I am working on a design for a larger shredder machine. A low speed high torque rotary style.

    I have calculated the maximum force needed to shear the materials. If I gear it down enough that the electric motor can deliver enough continuous torque, the RPM of the cutter is awfully slow, at about 0.75 RPM. I have already selected the highest HP motor rating that constraints will allow.

    The max amount of torque (or force at the cutter) will be necessary only occasionally.

    I am looking into the option of running the cutters at a higher RPM but storing energy in a flywheel so that the momentum can apply enough torque to complete the shear process when a thick material is encountered.

    I have made two sets of computations for my gear train. One set of computations lists each gear stage's torque & RPM assuming no flywheel.

    The second set of computations involves each gear stage's torque & RPM at my preferred RPM at the cutter.

    For a given RPM of gear (such as 500 RPM), I want to compute how much mass of a chosen circumference of solid flywheel is required to store and deliver the calculated difference of torque.

    In other words, I know how much maximum intermittent torque I need at the final stage and I know the smaller number of how much torque I will have at my selected operating RPM.

    Further upstream in the gear train where speeds are more like 500 RPM, I want to compute for a flywheel, but I don't fully understand how.

    I think the answer incorporates the rate of deceleration (which I think I can approximate based on how quickly the cutter traverses enough degrees to complete a shear) and moment of inertia. I have stared at some of the equations, but it has not yet "clicked."

    I don't want to oversize the flywheel, as I also need be sure the torque stays below the maximum amount (of force) that my knife cutting edge can handle before yield. Likewise for the gear teeth.

    Can you help me to get pointed in the right direction?


  2. #2
    Lead Engineer
    Join Date
    Aug 2013
    Houston TX USA
    Your best choice would be to use an energy exchange calculation. There are a number of online sites to help you calculate the kinetic energy of a rotating disc; and, calculate the energy required to shear your material. This will show you how much reduction in the flywheel rpm will occur during the cut; and, must be recovered by the motor before the next cut. The time to achieve that will be based upon the flywheel inertia vs motor torque ratio.

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