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Operating Torque out of Flywheel

  1. Mar 3, 2015 #1
    1. The problem statement, all variables and given/known data
    Hello, we have built a system in which energy is harvested through the use of an oscillating fin, this energy is stored within a flywheel which operates at a frequency f, we are then connecting this flywheel, via a smaller gear (gear ratio = 10) to an induction motor which should generate electricity.

    The induction motor has a set Operating Torque (it is variable but an example would be 3.86Nm) and Speed (once again variable but an example is 1380) it must operate at to generate the desired amount of power. We are controlling the speed it must operate at using the gear system to gear up the rotational speed of the flywheel, however we are struggling to confirm if the correct amount of Torque will be carried through to let the induction motor generate the correct amount of power.

    We know the total amount of energy stored in the flywheel (area under the power curve) and we know what the power curve for the oscillating fin is. We also know the dimensions of the flywheel and therefore the dimensions for the smaller gear connected to the induction motor.

    2. Relevant equations

    E = 1/2*w^2*I
    Work = Force * Distance
    Power = Tw

    3. The attempt at a solution
    I have initially used to the instantaneous power harvested by the fin and divided it by the angular velocity to find the instantaneous Torque however these values seem much too high, (typically find about 8e4 Nm using this method).

    I believe that the answer is related to the radius of the smaller gear, and the Force exerted on the belt round the gear, this will equal the torque acting on the centre of the smaller gear and therefore the torque acting on the induction motor. However I do not know how to find the force being exerted on the smaller gear. Is it possible to find this using the energy stored in the flywheel for 1 cycle or using the instantaneous power curve for 1 cycle?
  2. jcsd
  3. Mar 4, 2015 #2


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    That should give the right answer. Can you show your working?

    Gearing up the rpm gears down the torque. So increasing the rpm by a factor of 10 reduces the torque by a factor of 10.

    If there are any friction losses in the small gear bearings those appear magnified by 10 at the flywheel. In general stepping up is a bad idea. Could you use a different motor with more turns and a direct drive?

    PS: I'm away from my computer for the next few days but hopefully another person can help.
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